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The fat storage system

Perhaps not a very sexy name but why name it something else than what it is?

After studying the functioning of our lipoproteins for a good 2 years (and still not finished learning!), it has finally become clear what those lipoprotein are meant for. As complex as it may be, the end goal is really simple:

To facilitate the storage of fat
To prepare for the storage of fat
To recuperate storage structure when it is no longer needed
Transfer fat storage from one location to another

Compare it with the complexity of a swiss watch. All that mind-boggling complexity of the internal components, in the end to simply show you the hour, minutes and seconds.

I want to show you how these lipids relate to the storage objective. Not only that, by understanding how it functions I also want to provide a perspective on how the system can be protective of atherosclerosis, indeed even reverse plaque formation (!)

A very bold claim to make indeed. Just consider it speculative from my side. I present you the info and you make up your own mind. It will never be substantial until research is done to elucidate this further.

What I’m going to present you now, although elaborate, is still a simplified picture. Elaborate enough to show how the system works and simplified enough to show the most important components.

The basics

This picture, for most people who have already looked into the lipids, will be fairly familiar.

Dietary fat gets stored in adipose tissue
1st phase delivery is done by chylomicrons
2nd phase delivery is done by the interplay of various lipoprotein (VLDL, IDL, LDL, HDL)

The role of liver-produced lipids and cholesterol

The fat needs to be pushed in a lipid droplet which resides inside the fat cell. So both the lipid droplet and the fat cell need to expand. They both have a membrane so the membrane needs to expand as well and that requires phospholipids and cholesterol.

Those phospholipids and cholesterol come from the liver-produced lipoprotein (VLDL, IDL, LDL). Keep those phospholipids in mind when you see growing or shrinking lipid storage because I won’t mention them any further.

Not important for the system although interesting, the type of fatty acids used to make up the phospholipids will determine how much stability is required and thus how much cholesterol will be absorbed in the membrane. This is why cholesterol values can vary depending on the type of fat you eat.

When we get into the fasted state, the fat cells will start to release the fat. Now the reverse happens. Both the lipid droplet and the fat cell will shrink so they need to reduce their membranes and thus also release the cholesterol that is in it.

This means the cell will have too much cholesterol and will get rid of it via HDL.

The fat goes out of the fat cells and will be used throughout the body. In the muscle cells specifically, the cells will store the lipids that may have been reduced from previous activity. So here the lipid droplets will grow and, you guessed it, also here the membrane of the droplet requires cholesterol.

At the bottom left you see the shrinking lipid content represented of the fat cells while on the bottom right you have the growing lipid content of the muscle cells.

As we proceed longer into the fasted state, the muscle reaches an equilibrium where the size of the lipid droplet is maintained at a roughly equal size. Keep in mind though, there is a high turnover in the lipid droplet. So there is a continuous breakdown and buildup of triglycerides but the end result is essentially zero change in size. There is no need for additional cholesterol or the removal of cholesterol.

Before the lipoprotein can support this delivery of membrane components, they must have the right composition. This change in composition is facilitated by cholesterol ester transfer protein (CETP). The liver produces CETP under stimulation of insulin so the level of insulin drives the level of CETP activity.

With CETP:

HDL-C exchanges cholesterol for triglycerides (TG) with VLDL, IDL and LDL (ApoB100 containing lipoprotein)
HDL is dedicated to remodeling ApoB100 lipoprotein
This means that VLDL, IDL and LDL lose their TG and in return gain cholesterol. They become cholesterol-enriched.
This also means that HDL loses its cholesterol content and increases its TG content.
By being TG-rich, more HDL will be taken up by the liver creating lower circulating HDL particles in the blood
By being cholesterol-enriched, ApoB100 lipoprotein can be taken up by the cells

Without CETP:

HDL cannot offload its cholesterol to the ApoB100 lipoprotein and instead stays in circulation longer and accumulates more cholesterol
HDL is dedicated to cholesterol collection from cells
ApoE and LCAT drive HDL cholesterol accumulation so that it becomes big enough for uptake by the liver
The ApoB100 lipoprotein remain rich in TG and cannot be taken up by the cells

This is already becoming complex but you get a picture of how important CETP is. CETP will come back when we look at atherosclerosis..

Also note in the illustrations above, the free fatty acids aka non-esterified fatty acids (NEFA) (meaning not bound their usual glycerol backbone) are transported via albumin. This is an abundant available protein responsible for transporting the energy itself that will be used directly in the cells and also will be esterified (binding to glycerol) as triglycerides and stored in the lipid droplets inside the cells.

Getting everything across the cell membrane

There are 2 important factors to absorb the fatty acids and membrane structures. Note again, we focus primarily on cholesterol although the phospholipids are part of it.

These are not just gates that are open 100%, accepting anything at all times. How are they regulated? How do we get the NEFA and cholesterol across?

LPL

ApoC-II reduces on a high fat diet. This means that more NEFA is imported via albumin
Sterol regulatory element-binding protein 1 (SREBP1) is activated under lower cellular cholesterol content and reduces LPL expression
- => This is a negative feedback which reduces NEFA import. When there is a shortage of cholesterol to build storage then you need to lower NEFA to avoid accumulation in the cell
The fat cell LPL is activated by insulin. Muscle cell LPL is activated by low insulin
- => Insulin prioritizes fat storage in fat cells. => When insulin lowers, the energy is distributed and taken up by the other cells
LPL is increased during and after exercise. During those moments, there is an increased demand for energy

LDLr

Requires cholesterol-rich lipoprotein (VLDL, IDL, LDL)
Endocytosis of the lipoprotein (complete uptake of the lipoprotein)
Support expansion of the lipid droplet membrane via cholesterol import
Insulin activates SREBP1 and SREBP1 activates LDLr. As expected because SREBP1 shows there is a need for cholesterol and when driven by insulin it means we are focusing on storing fat.

LDLr in the muscle

exercise, fasting activates SREBP1 via MAPK. Similar to insulin, we also want to store fat simply to respond to a higher fat metabolism need. When fat metabolism increases, there is need for a bigger local buffer, a bigger lipid droplet.

In summary so far, we can say that a diet existing out of high fat quantities in combination with a high fat metabolism causes a continuous growing and shrinking of the fat cells. If that is combined with exercise then also the muscles are faced with this growing and shrinking. The timeframe and the volume of fat handled causes those cells and lipid droplets to grow to larger sizes and to shrink to smaller sizes, compared to a diet and lifestyle where glucose is a major energy source. This leads to a lower flux of the fat storage.

Such an intensified remodeling on high fat/high activity requires more support from the circulating lipoprotein!

This has to be supported by the lipoproteins that we are familiar with. VLDL, LDL and HDL. Moreover, in order to be able to receive the next bolus of incoming fat it is good to have the right types and level of lipoprotein ready to support this.

What is the best way to accommodate a high fat meal so that we can swiftly provide the necessary membrane components for expansion?

TG-rich (large buoyant) LDL
High cholesterol levels on HDL

When the meal comes in, insulin comes up and will stimulate CETP. With those 2 listed above, CETP can immediately remodel LDL to become enriched with cholesterol so that it can be taken up by the fat cells. Both lipoproteins need to be sufficiently high to support a faster clearance of the fat into storage.

It’s my engineer thinking but would it be just a coincidence that LDL goes up under such high fat intake and consumption? This high flux signals the need for a greater storage capacity so doesn’t it make sense to have more of the membrane components ready to maximize the storage capacity? Could that be the reason why fasting LDL particles and HDL cholesterol are high? As soon as CETP kicks into action you’ll now have a lot of LDL particles ready to accept cholesterol and support the membrane expansion of fat cells and their lipid droplets.
You NEED high LDL and HDL when you have a high dietary fat intake

High fasting LDL, HDL and low TG for lean individuals on a ketogenic diet

With the above information you understand the need for it. But how do we arrive at that situation? The following are general mechanisms that apply to everybody but the extend to which they get applied is determined by many factors such as the amount of fat you eat, exercise level, your level of insulin etc… There are other factors but insulin is a very big player in all of this.

Under fasted conditions, insulin is sufficiently low to keep cholesterol production very low. When fasted we are not interested in storing fat. The liver preserves most fatty acids for ketogenesis, bile production and its own fat metabolism. Both fatty acids and cholesterol production is low in such a way that it has shifted from VLDL production towards large buoyant LDL
Large buoyant LDL stays in circulation longer because it is cholesterol poor, ApoE rich and thus has a lower ability to be taken up by LDLr for endocytosis. That ApoE enrichment is also the reason why small dense LDL (sdLDL) has a lower affinity for LDLr
Low insulin keeps CETP low, thus VLDL and LDL cannot acquire sufficient cholesterol from HDL for endocytosis by LDLr
Due to low CETP, the cholesterol load on HDL increases and minimizes exchange with VLDL, IDL, LDL.
With very low to no production of VLDL sized lipoprotein, there are almost no lipoproteins that can acquire ApoC-II for lipolysis by LPL thus almost all skeletal muscle NEFA are derived from albumin

So on the production side we have lower production but more of the lipoprotein in the LDL size, in circulation there is no remodeling taking place and due to this the uptake by the skeletal muscle is much lower.

When the skeletal muscles are full and reduce their uptake of fatty acids, this will lead to a higher return of those fatty acids towards the liver. So the release of fatty acids from the fat cells is temporarily higher than the uptake by the other cells. This accumulation leads to a larger availability of fatty acids in the liver so that it can augment its production of TG-rich LDL.

Now it will depend on how big this discrepancy is. This higher level of fatty acids in the liver also causes more ketones (BHB) to be produced. The body may respond to this by slightly increasing insulin. This will cap BHB production, reduce the rate of fatty acid release from fat cells and slightly increase cholesterol production allowing the liver to temporarily produce more VLDL-sized lipoprotein. It will also slightly elevate CETP so that storage can be facilitated to get rid of the excess fat in circulation.

You may notice this as a slight elevation in your fasted triglycerides. It is only temporarily as it is part of an exercise to balance out demand and supply.

Buffering for energy usage

and issues with it

Still following so far? OK. Now lets have a look at issues with storage.

Just like with glucose, the fat is stored in large quantity in a central place and from there distributed to local storage in the muscle. Central is put in quotes, mainly referring to the adipocytes. It is supposed to sit under our skin and well.. our skin is completely wrapped around our body so it is a bit strange to say central.

I’ve illustrated glycogen here just for comparison. Just note that I’m continuing only talking about the fat.

Storage limitation -> muscle insulin resistance

At some point, all of these buffers have to signal when they are full and (temporarily) cannot take in any more fat. This signaling is provided by 1,2DAG. An intermediate fatty acid that is formed when synthesizing triglycerides for storage.

TG synthesis generates 1,2DAG
Accumulation leads to translocation of 1,2DAG into the cell membrane
1,2DAG attracts Protein Kinase C (PKC) to the membrane
PKC internalizes LDLr -> No uptake of cholesterol-rich lipoprotein
PKC inhibits Insulin Receptor Signaling (IRS) -> insulin resistance!

1,2DAG is preferentially hydrolyzed (broken down) for fat metabolism
Exercise, fasting, high fat diets increase fat metabolism
- Increased clearance of 1,2DAG via DGAT1 expression (exercise)
- Restores insulin sensitivity
- Increases SREBP1 expression -> increases LDLr expression -> increases lipid storage capacity

It does create a conflict though because the accumulation also indicates the need for more cholesterol but 1,2DAG prevents this by blocking LDLr. You cannot signal stop and store more at the same time so how do we end up in this situation?

Increased storage in lipid droplet reduces cellular cholesterol
lower cellular cholesterol -> SREBP1 activation -> increase LDLr expression
1,2DAG accumulation threshold blocks LDLr via PKC
- Prioritize cellular cholesterol production instead of via extracellular uptake
- Reduce cellular fatty acid accumulation

In and of itself this is a normal mechanism. By not taking up both lipids and membrane components, other cells can manage to top up their reserves so you get an even distribution. The problem however is when every cell is topped up and you still have too much in circulation.

It will lead to higher insulin levels because too much energy in circulation drives up insulin to try and store that excess. That will lead to more VLDL-bound TG, higher CETP thus higher cholesterol bound to LDL (higher cholesterol/particle ratio) and lower HDL.

But with cells that have enough fat accumulated, they say no to insulin so insulin does what it is supposed to do, form the lipoprotein particles that are required for storage but all the cells keep their doors closed.

Exactly the pathologic lipid profile that we know and should fear.

Increased VLDL triglycerides
Increased cholesterol-rich LDL
Decreased HDL (lower cholesterol/particle ratio)

Why should we fear it? Because it has a good proxy value towards atherosclerosis.

Atherosclerosis

saved by enhanced fat metabolism?

As mentioned in the introduction, it may actually mean reversal of plaque! The very low insulin obtained through being lean, very low carbohydrate diet with high fat intake creates cholesterol-enriched – ApoE-enriched HDL which drives up their LCAT activity. LCAT stimulates cholesterol release from macrophages.

Macrophages in atherosclerosis aren’t only gobbling up cholesterol, they also accumulate triglycerides. It turns out though that cholesterol efflux helps to switch gears into fat metabolism so the macrophage can reduce its fat storage. If you cannot store the fat, you have to start using it for energy.

This whole deep dive into research led me to the following, to my view important, observation. These M1 macrophages actually maintain import and storage of fatty acids (through LDLr). Only by ‘forcing’ cholesterol efflux are we able to reverse the situation, pushing them to metabolize the fat. PPARy is known to do this and PPARy is activated by BHB, thus a ketogenic diet. PPARy is also activated under low cellular cholesterol, via SREBP1. This has been evidenced in liver and fat cells but likely also applies to macrophages. And a deactivation of PPARy was accomplished by re-addition of cholesterol.

PPARy expression hence seems subject to a tight and fast control by alterations in intracellular cholesterol levels, and this effect is mediated by the SREBP family of transcription factors.
source: https://pubmed.ncbi.nlm.nih.gov/10409739/ “Regulation of peroxisome proliferator-activated receptor gamma expression by adipocyte differentiation and determination factor 1/sterol regulatory element binding protein 1: implications for adipocyte differentiation and metabolism”

A paper showed me that macrophages are able to restore insulin resistance in skeletal muscle of diabetics. Insulin resistance that is caused by 1,2DAG as we have seen. So if macrophages carry the capacity to somehow neutralize 1,2DAG from the membrane then maybe they apply this capacity also to their own membrane.

This is still an area I need to find research on but we already see that macrophages do not exhibit a stop mechanism like other cells.

That would explain why they get so big with fat and cholesterol. The only way out of this situation is to enhance the efflux of cholesterol from the macrophages. And the only way to do that is by creating big cholesterol-rich HDL so that it can acquire ApoE and drive up LCAT. And the only way to do that is by getting your insulin very low. And the only way to do that sustainably(!) is by adopting a very low carb diet and getting lean.

Get those cells to push out cholesterol like it’s nobodies business!

update 2021/09/21: A paper came out showing how BHB could be reversing vascular calcification through autophagy. Although it is separate from the described mechanism above, it does pertain to enhancing fat metabolism as a way to reverse the diseased state.

“β-Hydroxybutyric Inhibits Vascular Calcification via Autophagy Enhancement in Models Induced by High Phosphate.” https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC8422966/

—– T H E – E N D —–

Sources

My previous writings on this topic with references that over time have contributed to my understanding.

Further resources, specifically for this article

LXR

https://pubmed.ncbi.nlm.nih.gov/12697904/ “Activation of liver X receptor improves glucose tolerance through coordinate regulation of glucose metabolism in liver and adipose tissue”

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6433546/ “Liver X receptors in lipid signaling and membrane homeostasis”

Cholesterol efflux

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4159082/ “Cholesterol efflux and atheroprotection: Advancing the concept of reverse cholesterol transport”

https://pubmed.ncbi.nlm.nih.gov/17390217/ “Stimulation of lipolysis enhances the rate of cholesterol efflux to HDL in adipocytes”

Lipids on a ketogenic diet

https://academic.oup.com/jn/article/135/6/1339/4663837 “Modification of Lipoproteins by Very Low-Carbohydrate Diets”

LPL receptor

https://www.ncbi.nlm.nih.gov/books/NBK537040/ “Biochemistry, Lipoprotein Lipase”

https://www.sciencedirect.com/science/article/pii/S0022227520380901 “Effects of dietary carbohydrate and fat on plasma lipoproteins and apolipoproteins C-II and C-III in healthy men”

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5705268/ “Apolipoprotein C-II: New findings related to genetics, biochemistry, and role in triglyceride metabolism”

https://www.ahajournals.org/doi/full/10.1161/01.ATV.19.3.472 “Role of ApoCs in Lipoprotein Metabolism”

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5705268/ “Apolipoprotein C-II: New findings related to genetics, biochemistry, and role in triglyceride metabolism”

https://pubmed.ncbi.nlm.nih.gov/11090277/ “Induction of LPL gene expression by sterols is mediated by a sterol regulatory element and is independent of the presence of multiple E boxes”

LDL in skeletal muscle

https://pubmed.ncbi.nlm.nih.gov/9696990/ “Skeletal muscle lipoprotein lipase: molecular regulation and physiological effects in relation to exercise”

https://www.sciencedirect.com/science/article/pii/S0925443902001692 “Expression and regulation by insulin of low-density lipoprotein receptor-related protein mRNA in human skeletal muscle”

https://diabetes.diabetesjournals.org/content/50/11/2585 “In Muscle-Specific Lipoprotein Lipase−Overexpressing Mice, Muscle Triglyceride Content Is Increased Without Inhibition of Insulin-Stimulated Whole-Body and Muscle-Specific Glucose Uptake”

https://pubmed.ncbi.nlm.nih.gov/17046550/ “Fasting decreases free fatty acid turnover in mice overexpressing skeletal muscle lipoprotein lipase”

in liver

https://pubmed.ncbi.nlm.nih.gov/12951168/ “Mechanisms of HDL lowering in insulin resistant, hypertriglyceridemic states: the combined effect of HDL triglyceride enrichment and elevated hepatic lipase activity”

LDL receptor

https://www.ahajournals.org/doi/10.1161/circresaha.114.301621 “PCSK9 – A key modulator of cardiovascular health”

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3071588/ “Activation of LDL Receptor (LDLR) Expression by Small RNAs Complementary to a Noncoding Transcript that Overlaps the LDLR Promoter”

https://pubmed.ncbi.nlm.nih.gov/16449296/ “Exercise training and calorie restriction increase SREBP-1 expression and intramuscular triglyceride in skeletal muscle”

https://diabetes.diabetesjournals.org/content/69/5/848 “Exercise and Muscle Lipid Content, Composition, and Localization: Influence on Muscle Insulin Sensitivity”

https://pubmed.ncbi.nlm.nih.gov/9010277/ “Low density lipoprotein receptor expression and function in human polymorphonuclear leucocytes”

https://pubmed.ncbi.nlm.nih.gov/3237238/ “The binding of lipoproteins to human muscle cells: binding and uptake of LDL, HDL, and alpha-tocopherol”

https://journals.physiology.org/doi/full/10.1152/ajpendo.00543.2005 “Exercise training and calorie restriction increase SREBP-1 expression and intramuscular triglyceride in skeletal muscle”

https://www.cell.com/fulltext/S0092-8674(00)80213-5 “The SREBP Pathway: Regulation of Cholesterol Metabolism by Proteolysis of a Membrane-Bound Transcription Factor”

https://www.ahajournals.org/doi/full/10.1161/01.ATV.18.3.466 “Influence of ApoE Content on Receptor Binding of Large, Buoyant LDL in Subjects With Different LDL Subclass Phenotypes”

https://pubmed.ncbi.nlm.nih.gov/8254047/ -> https://dm5migu4zj3pb.cloudfront.net/manuscripts/116000/116915/cache/116915.1-20201218131521-covered-253bed37ca4c1ab43d105aefdf7b5536.pdf “Accumulation of “small dense” low density lipoproteins (LDL) in a homozygous patients with familial defective apolipoprotein B-100 results from heterogenous interaction of LDL subfractions with the LDL receptor”

https://pubmed.ncbi.nlm.nih.gov/16670767/ “Putting cholesterol in its place: apoE and reverse cholesterol transport”

Lipids

https://www.sciencedirect.com/science/article/pii/S0022227520380901 “Effects of dietary carbohydrate and fat on plasma lipoproteins and apolipoproteins C-II and C-III in healthy men”

https://www.britannica.com/science/lipid/Classification-and-formation “Classification and formation”

Macrophages

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3767414/ “Lipid Droplets And Cellular Lipid Metabolism”

https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0056601 “Skeletal Muscle Insulin Resistance Associated with Cholesterol-Induced Activation of Macrophages Is Prevented by High Density Lipoprotein”

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1868788/ “Macrophage PPARγ is required for normal skeletal muscle and hepatic insulin sensitivity and full antidiabetic effects of thiazolidinediones”

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3957345/ “High-Density Lipoprotein Maintains Skeletal Muscle Function by Modulating Cellular Respiration in Mice”

https://pubmed.ncbi.nlm.nih.gov/29217413/ “Apolipoprotein E-containing high-density lipoprotein (HDL) modifies the impact of cholesterol-overloaded HDL on incident coronary heart disease risk: A community-based cohort study”

https://pubmed.ncbi.nlm.nih.gov/16670775/ “HDL from CETP-deficient subjects shows enhanced ability to promote cholesterol efflux from macrophages in an apoE- and ABCG1-dependent pathway”

https://www.nature.com/articles/aps201093 “A novel model of cholesterol efflux from lipid-loaded cells”

https://www.cell.com/cell-metabolism/references/S1550-4131(07)00166-0 “PPARγ Activation Primes Human Monocytes into Alternative M2 Macrophages with Anti-inflammatory Properties”

https://pubmed.ncbi.nlm.nih.gov/22207731/ “Regulation of lipid droplet cholesterol efflux from macrophage foam cells”

https://www.nature.com/articles/s41598-018-34305-x “A reduced M1-like/M2-like ratio of macrophages in healthy adipose tissue expansion during SGLT2 inhibition”

Lipid droplet

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4575688/ “DAG tales: the multiple faces of diacylglycerol—stereochemistry, metabolism, and signaling”

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4526153/ “The Biophysics and Cell Biology of Lipid Droplets”

Muscle cell

https://www.sciencedirect.com/science/article/pii/S0005273615003867 “Alteration of lipid membrane structure and dynamics by diacylglycerols with unsaturated chains”

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1665384/ “High triacylglycerol turnover rate in human skeletal muscle”

https://journals.physiology.org/doi/full/10.1152/ajpendo.00543.2005 “Exercise training and calorie restriction increase SREBP-1 expression and intramuscular triglyceride in skeletal muscle”

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1866250/ “Upregulation of myocellular DGAT1 augments triglyceride synthesis in skeletal muscle and protects against fat-induced insulin resistance”

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3510842/ “Studies on the Substrate and Stereo/Regioselectivity of Adipose Triglyceride Lipase, Hormone-sensitive Lipase, and Diacylglycerol-O-acyltransferases”

Dawn phenomenon

https://joe.bioscientifica.com/view/journals/joe/231/3/235.xml “Melatonin modifies basal and stimulated insulin secretion via NADPH oxidase”

https://pubmed.ncbi.nlm.nih.gov/6368151/ “Fasting early morning rise in peripheral insulin: evidence of the dawn phenomenon in nondiabetes”

PPARy

https://pubmed.ncbi.nlm.nih.gov/10409739/ “Regulation of peroxisome proliferator-activated receptor gamma expression by adipocyte differentiation and determination factor 1/sterol regulatory element binding protein 1: implications for adipocyte differentiation and metabolism”

Bone health on a ketogenic diet

Pulling the final plug on attacks

Attacks? I follow up on all published papers related to ketogenesis and although the execution may be done correctly and data may be generated correctly.. the circumstances are often specific and the conclusions are stretched beyond the scope of what the data is representing or can represent. All to fulfill the personal bias.

“A Short-Term Ketogenic Diet Impairs Markers of Bone Health in Response to Exercise” https://www.frontiersin.org/articles/10.3389/fendo.2019.00880/full?utm_source=F-NTF&utm_medium=EMLX&utm_campaign=PRD_FEOPS_20170000_ARTICLE

Why? The ketogenic diet is the very opposite of what is generally recommended as the ideal diet. High in (animal sourced) fat, for sure leaving out seed oils, sufficient protein and drastically limiting carb intake. This goes against what nutritionists have learned and recommend and similarly for anyone in the medical field. It is completely opposite to the ideology of other diets such as veganism.

So you can imagine it generates skepticism and enemies from different areas. Apart from clashing with personal conviction, it also threatens a whole carb-centric industry and a pharma industry that relies on managing disease rather than handing the root cause and curing disease.

Since I got interested in the ketogenic diet and metabolism in general, I have found nothing left of the original negative claims and ‘dangers’ following a ketogenic diet (KD) except for impaired performance at very high intensities such as in endurance racing although I have a theory on how to fix that.

One last element on the list is bone health. This keeps on being a topic that comes up regularly and with this post I want to dig in deeper to understand what bone health means and what can we expect from a KD.

A first signal that made me question current dogma was when looking at pro cyclists versus amateurs. The pro cyclists had lower bone mineral density (BMD) and lower bone mineral content (BMC), both considered markers of bone health.

“Professional cyclists have lower levels of bone markers than amateurs. Is there a risk of osteoporosis in cyclist?” https://www.sciencedirect.com/science/article/abs/pii/S8756328221002672?via%3Dihub

Pro’s spend a lot more time sitting on their bike and generally are one of the most lean athletes so low weight. When we look at the elite of the elite, Tour de France contestants, then we don’t see the types of fractures (clavicle, wrist, hand, femure) represented by the location where low BMD is found (femoral neck, total hip, lumbar spine).

“Prevalence and Epidemiology of Injuries Among Elite Cyclists in the Tour de France” https://pubmed.ncbi.nlm.nih.gov/30202769/ “A Systematic Review of Bone Health in Cyclists” https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC3230645/

These guys crash at high speeds, off cliffs, against walls etc.. Perhaps we think we understand bone health but do we really?

Understanding bone health

Most people do not think about bones as a dynamic thing but constant remodeling is taking place. Remodeling is taken care of by osteoclasts which break down old and damaged bone while new bone is formed by osteoblasts. A proper balance needs to be maintained between both to support healthy bone and adaptive towards increasing resistance to higher forces such as from resistance exercise and stronger muscle.

Remodeling itself may need to be flexible, increasing when needed and reducing when not required as much.

In studies we find tartrate‑resistant acid phosphatase (TRAP) and collagen degradation via C-terminal telopeptide (CTX) used as a marker of bone resorption while alkaline phosphatase (ALP) and procollagen 1 N-terminal propeptide (P1NP) as a marker of bone formation.

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“Disorders of Bone Remodeling” https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC3571087/

Often we can look at studies that investigated and found causes of increased fractures such as the next one looking at Type 2 Diabetes (T2D). Due to lower levels of osteocalcin (vitamin K and D deficiency) and bone remodeling, patients have normal BMD but increased risk of fracture. They specifically point out the bad damaged structure rather than BMD as a cause of the higher risk.

According to the article, osteoblasts/osteocytes are impacted in viability and reduces dendrite connectivity through high reactive oxygen species (ROS) when metabolizing glucose. They need a high anti-oxidant defense which is brought up by increased fat metabolism through glutathione.

The following chart is complex but their argument is that decreased bone health is driven by hyperinsulinemia. A KD keeps your insulin very low. One of the results of a higher reliance on carbs is that there are more advanced glycation end products (AGEs) formed. They end up creating cross-links between the collagen, just like the CTX, making the bones more stiff.

“Rethinking Fragility Fractures in Type 2 Diabetes: The Link between Hyperinsulinaemia and Osteofragilitas” https://www.mdpi.com/2227-9059/9/9/1165

Collagen in the bone is enzymatically cross-linked with each other to provide stiffness. This cross-linking under normal conditions is done by dihydroxylysinonorleucine (DHLNL), hydroxylysinonorleucine (HLNL) and lysinonorleucine (LNL) which are considered the immature links. These substances are easier extracted yet with a lower yield from osteoporotic patients. Over time they further evolve towards mature cross-links pyridinoline (PYD) and deoxypyridinoline (DPD).

The second paper below indicates that especially the immature cross-links are reduced when in competition with AGEs.

Correlations between each of the lysine-derived AGEs (i.e. CML, CEL and pentosidine), and the enzymatic cross-links were analyzed because these AGEs possibly compete with enzymatic crosslinks for formation sites³⁶. The amounts of DHLNL, HLNL, and LNL were negatively correlated with CML, CEL and pentosidine, whereas no such correlation was observed for PYD and DPD (Table 5).

“Reduced concentration of collagen reducible cross links in human trabecular bone with respect to age and osteoporosis” https://pubmed.ncbi.nlm.nih.gov/8922646/ “Mass spectrometric quantitation of AGEs and enzymatic crosslinks in human cancellous bone” https://www.nature.com/articles/s41598-020-75923-8

A further look at T2D confirms the same story. AGEs replace the enzymatic cross-links, increased osteoclast activity and reduction in osteoblast activity.

The aggregation of AGEs causes non-enzymatic cross-linking of collagen, disrupting the adhesion of osteoblasts to the extracellular matrix and resulting in bone fragility [16] (Fig. 3). These alterations of extracellular matrix also reduce alkaline phosphatase (ALP) activity in mature osteoblasts, affecting bone mineralization [16]. The receptor for AGEs (RAGE) is expressed in human bone cells and its stimulation drives the activation of nuclear factor kappa-B (NF-kB) in osteoclasts, increasing the production of cytokines and reactive oxygen species (ROS) [17]. High proinflammatory cytokine and ROS levels trigger osteoclastogenesis and stop osteoblast differentiation [18, 19].

“Diabetes and Bone Fragility” https://link.springer.com/article/10.1007/s13300-020-00964-1

We can start to doubt if BMD and BMC are good markers of bone health. Bone health lays within the structure but that is not something you can easily measure. DEXA scans give you BMD and BMC but nothing on the integrity.

In line with the effect seen in T2D, we also see how sugar sweetened beverages (SSB) have an inverse association with bone mineral density (BMD).

“Sugar-sweetened beverage consumption and bone health: a systematic review and meta-analysis” https://nutritionj.biomedcentral.com/articles/10.1186/s12937-021-00698-1

To me, this starts to show that BMD and BMC are not quality markers. Looking at a few more studies we find a roughly 50% division for fractures in older adults above and below the WHO determined level for osteoporosis. That makes fracture prediction based on BMD basically a flip-of-a-coin.

“Fracture incidence and association with bone mineral density in elderly men and women: the Rotterdam Study” https://pubmed.ncbi.nlm.nih.gov/14751578/ – “Identification of osteopenic women at high risk of fracture: the OFELY study” https://pubmed.ncbi.nlm.nih.gov/16160738/

Perhaps the combination of these factors, stiffness and lower BMD is something to worry about than either alone?

CTX

CTX exists in different forms. The alpha version, left side on the image below, shows declining levels as we age. Generally everything declines as we age, all for the worse.

“The contribution of collagen crosslinks to bone strength” https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC3868729/

Is it possible that we see a decline in CTX because AGEs are replacing them and cannot be broken down so easily?

Vitamin K2

Deficiency in vitamin K2 (vK2) is a factor that could also lead to poor bone health. One of the vK2 effects noted in osteoclast is the inhibition of NF-kB. Too much osteoclast activity and you get weaker bones.

“The Dual Role of Vitamin K2 in “Bone-Vascular Crosstalk”: Opposite Effects on Bone Loss and Vascular Calcification” https://www.mdpi.com/2072-6643/13/4/1222

Vitamin D

Vitamin D has an important role in bone formation. The active form of vitamin D is calcitriol (1,25-dihydroxycholecalciferol). Calcitriol is beneficial to bone formation by inhibiting the osteoclasts and promoting the osteoblast activity.

“Association of Anabolic Effect of Calcitriol with Osteoclast-Derived Wnt 10b Secretion” https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC6164019/

Under chronic high fructose intake the levels are reduced.

“Chronic High Fructose Intake Reduces Serum 1,25 (OH)2D3 Levels in Calcium-Sufficient Rodents” https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0093611

Fatty acids

Capric acid also reduces osteoclast activity. But again, it is the balance between osteoclast and osteoblast activity that generates healthy bones.

“A medium-chain fatty acid, capric acid, inhibits RANKL-induced osteoclast differentiation via the suppression of NF-κB signaling and blocks cytoskeletal organization and survival in mature osteoclasts” https://pubmed.ncbi.nlm.nih.gov/25134536/

Different fatty acids have different effects. Here we see octanoic acid and decanoic acid analyzed. Primarily octanoic acid showed a reduction in ALP and increase in TRAP.

“Octanoic acid a major component of widely consumed medium-chain triglyceride ketogenic diet is detrimental to bone” https://www.nature.com/articles/s41598-021-86468-9

Thyroid

In a group of familial longevity they found lower bone turnover markers. Increase in TSH was followed by increase in CTX and P1NP so breakdown and buildup respectively.

“Familial longevity is associated with lower baseline bone turnover but not differences in bone turnover in response to rhTSH.” https://pubmed.ncbi.nlm.nih.gov/34491903

Acidity

One other acid, induced by diet is uric acid. Fructose intake is a direct result of increased uric acid. Sugar and high fructose corn syrup are major sources of fructose, both via solid and liquid intake. These are highly avoided on a KD.

“Recent advances in fructose intake and risk of hyperuricemia” https://www.sciencedirect.com/science/article/pii/S0753332220309884

Fructose not only causes increased uric acid, it also impairs calcium absorption via the gut.

“Dietary Fructose Inhibits Intestinal Calcium Absorption and Induces Vitamin D Insufficiency in CKD” https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC2834550/

This is very important because calcium is not only used for bone formation but also for metabolism. With a reduction from the diet, the bones have to give up more calcium to fulfil the needs in the metabolic processes.

Protein

It is so important that it deserves its own chapter. The impact of low dietary protein is often a cause for the noted reduction in bone health and growth stunting in children.

Animal protein stimulates growth more than plant-based protein in children.

“Dietary Intake of Protein in Early Childhood Is Associated with Growth Trajectories between 1 and 9 Years of Age” https://academic.oup.com/jn/article/146/11/2361/4630467

dietary protein is a key nutrient for bone health across the life span and therefore has a function in the prevention of osteoporosis.⁹ Protein makes up roughly 50% of the volume of bone and about one-third of its mass.¹⁰
“Optimizing Dietary Protein for Lifelong Bone Health” https://journals.lww.com/nutritiontodayonline/fulltext/2019/05000/optimizing_dietary_protein_for_lifelong_bone.5.aspx

It should be no surprise that insufficient protein is detrimental for bone formation.

“Protein intake and bone growth” https://pubmed.ncbi.nlm.nih.gov/11897891/

In the elderly population, if anything, we see a reduction in hip fracture with increasing protein. I’m not so happy with these studies non-RCT studies as possible positive effects can be impaired by negative confounders such as high glucose and fructose intake.

“Protein intake and risk of hip fractures in postmenopausal women and men age 50 and older” https://link.springer.com/article/10.1007%2Fs00198-016-3898-7 – “Does dietary protein reduce hip fracture risk in elders? The Framingham osteoporosis study” https://link.springer.com/article/10.1007%2Fs00198-010-1179-4 – “Risk Factors for Hip Fracture in Older Men: The Osteoporotic Fractures in Men Study (MrOS)” https://asbmr.onlinelibrary.wiley.com/doi/10.1002/jbmr.2836 – “The Association Between Protein Intake by Source and Osteoporotic Fracture in Older Men: A Prospective Cohort Study” https://asbmr.onlinelibrary.wiley.com/doi/10.1002/jbmr.3058

In the following study we see that particularly a vegan diet is associated with increased fracture. A hazard ratio of 2.31 is meaningful. This is of course just association but perhaps the info further down can help to clarify potential reasons.

“Vegetarian and vegan diets and risks of total and site-specific fractures: results from the prospective EPIC-Oxford study” https://bmcmedicine.biomedcentral.com/articles/10.1186/s12916-020-01815-3

In a healthy population, increased dietary protein resulted in increased urinary calcium excretion but this was paralleled with an increase in calcium absorption.

“Dietary protein, calcium metabolism, and skeletal homeostasis revisited” https://academic.oup.com/ajcn/article/78/3/584S/4690000?login=true

Fractures

Racing bikes are made of a carbon frame. These are very stiff and very strong but only when the force is applied in the right direction. Parallel to the tube, not sideways. Sideways they don’t bend, they snap like a dry twig. Could the same be the case for our bones?

AGEs

One potential contributor to decreased bone health is pentosidine which is an AGE. We saw before that AGEs form bad quality collagen links, creating stiffer bones.

Pentosidine content in bone tends to increase in an age-dependent manner, and different diseases can accelerate the accumulation of pentosidine. Studies in animal models of type 2 diabetes, type 1 diabetes, low and high turnover chronic kidney disease, and postmenopausal osteoporosis have shown elevated levels of bone pentosidine and altered amounts of enzymatic cross-links (lysyl oxidase [LOX]-dependent cross-links). As these diseases are also associated with higher fracture risk, the hypothesis is that pentosidine contributes to fracture risk.
“Pentosidine as a Biomarker for Poor Bone Quality and Elevated Fracture Risk” https://link.springer.com/referenceworkentry/10.1007%2F978-94-007-7693-7_32

Since glycation is often reported as glucose binding with protein, it is often forgotten that fructose (fructation) has an even bigger effect, up to 10-fold higher!

“Nonenzymatic glycation of bovine serum albumin by fructose (fructation). Comparison with the Maillard reaction initiated by glucose” https://pubmed.ncbi.nlm.nih.gov/2537288/

Not only within the body but also via our diet do we ingest AGEs. This Japanese study looked at common food and drinks. At the bottom end we see milk, coffee and tea but the top shows sugar and fructose containing drinks for the most part.

“Assessment of the Concentrations of Various Advanced Glycation End-Products in Beverages and Foods That Are Commonly Consumed in Japan” https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0118652

Such dietary AGEs and endogenously produced ones depend on good filtration capability of the kidneys, which are impaired under metabolic syndrome.

“Studies on Absorption and Elimination of Dietary Maillard Reaction Products” https://nyaspubs.onlinelibrary.wiley.com/doi/abs/10.1196/annals.1333.054

To no surprise, people who suffer from chronic kidney disease have elevated serum AGEs and this is reflected in their bones with increased fracture risk.

Pentosidine was remarkably increased in dialysis patients and inversely correlated with bone-formation rate/bone volume and mineral apposition rate. This study suggests that AGE collagen cross-links strongly associate with disorders of bone metabolism in dialysis patients.
“Nonenzymatic cross-linking pentosidine increase in bone collagen and are associated with disorders of bone mineralization in dialysis patients” https://pubmed.ncbi.nlm.nih.gov/21499867/

The enzymatic cross-links is what we want, not pentosidine. By increasing the enzymatic ones and removing pentosidine, we see in the following study an increase in strength. Both calcium content and these enzymatic cross-links were each independently responsible for increased strength. Also in this study they reaffirm that the cross-links determined stiffness.

“Changes in the contents of enzymatic immature, mature, and non-enzymatic senescent cross-links of collagen after once-weekly treatment with human parathyroid hormone (1-34) for 18 months contribute to improvement of bone strength in ovariectomized monkeys” https://pubmed.ncbi.nlm.nih.gov/20959962/

Impact on a ketogenic diet

A KD avoids carbs and fructose in the diet especially from sugar and high-fructose corn syrup (HFCS) and sugar containing beverages, even ‘natural’ fruit drinks which are also high in carbs.

So a reduction in glucose which forms AGEs, a normal or increased calcium uptake due to lower fructose, lower uric acid due to low fructose and sufficient protein.

The diet generally elevates vitamine D and K2 sources and allows stored vitamine D to be released from adipose as weight is lost.

Not only vK2 can suppress NF-kB but also a ketogenic diet.

“Ketogenic diet attenuates oxidative stress and inflammation after spinal cord injury by activating Nrf2 and suppressing the NF-κB signaling pathways” https://pubmed.ncbi.nlm.nih.gov/29894768/

Following an 8-week KD, women on resistance training had a small significant improvement in BMD compared to the normal diet (0.02 versus 0.00 g/cm2).

“Effects of a low-carbohydrate ketogenic diet on health parameters in resistance-trained women” https://link.springer.com/article/10.1007%2Fs00421-021-04707-3

After 12 weeks on a KD, there were no differences found in BMD.

“Keto-adaptation enhances exercise performance and body composition responses to training in endurance athletes” https://www.metabolismjournal.com/article/S0026-0495(17)30298-6/fulltext

A thorough review of bone remodeling and ketogenic diet has been done before but they somewhat left out the impact of dietary protein. A must-read though to get a better understanding in general. It covers a lot of murine studies. Important is that a KD for these animals usually involves highly restricted protein intake.

“Energy Metabolism and Ketogenic Diets: What about the Skeletal Health? A Narrative Review and a Prospective Vision for Planning Clinical Trials on this Issue” https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC7796307/

Following up epileptic children who followed a modified Atkins diet (MAD), less restrictive in protein, they found no impact on bone health. Normal bone mass and growth.

“Prospective study of growth and bone mass in Swedish children treated with the modified Atkins diet” https://pubmed.ncbi.nlm.nih.gov/31085021/

Acidity

A KD is typical because it raises the production of beta-hydroxybutyrate (BHB) which is an acid. You could quickly jump to conclusion that this acid needs to be neutralized by binding to calcium leading to calcium deprivation impacting bone formation.

What we do notice is that the pH is maintained within the required range (7.35 – 7.45). A KD reduces the production of CO2 which is also an acid.

I don’t have data to support the following claim but I think it makes sense. When the diet can supply sufficient calcium then it is likely that the balance is kept to deal with acidity so that the bones are not impacted.

The dietary sources on a ketogenic diet are sufficiently high in calcium and the level of protein intake should support calcium requirements.

Protein

Some people claim that protein intake is responsible for acidity. Proteins are made up of amino acids thus indeed also acidic. But a thorough study measuring urine pH, acid excretion and calcium excretion found no relationship with fractures in a long follow-up study of 5 years, including no change in BMD.

“Low urine pH and acid excretion do not predict bone fractures or the loss of bone mineral density: a prospective cohort study” https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC2890599/

It even seems that protein help to clear uric acid!

“The uric acid lowering effect of protein-rich diets. Behavior of human uric acid metabolism under reducing diet forms with varied protein content” https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC2890599/

Studies in mice and rats often involve heavy restriction of protein in the diet. Could that influence the results? This is definitely a confounder.

AGEs

This study concluded a low carbohydrate diet reduced renal AGE formation.

“Low-Carbohydrate Diet Inhibits Different Advanced Glycation End Products in Kidney Depending on Lipid Composition but Causes Adverse Morphological Changes in a Non-Obese Model Mice” https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC6893679/

Summary

Bone Mineral Density is not an indication of bone health. Bone health and remodeling can be impacted by many factors.

Increased force requires more remodeling to create a higher density.
When switching from a diet that is detrimental for bone health towards one that is good for bone health may be marked by a temporal increase in breakdown markers, especially CTX.
Protein in the diet needs to be sufficient. Restricting it too severe such as in animal studies and often in children treated for epilepsy on a KD, will lead to reduced bone density.
Something we see in astronauts is that they lose 1% to 2% of BMD every month. Weight loss reduces the strength requirements so we can expect a little reduction in BMD noticeable via higher breakdown activity.
Adequate nutritional status of vK2 and calcitriol are important bone mass forming agonists and together with a KD reduce bone breakdown activity.

“What happens to bones in space?” https://www.asc-csa.gc.ca/eng/astronauts/space-medicine/bones.asp

So when studies report a negative effect on BMD then we need to look at all these effects and evaluate whether we are looking at a desired effect or an impaired situation.

The only objective markers for bone health can be found on incidences of fracture rates.

As long as we don’t see an increase in weight lifters and endurance athletes, who have a higher dependency on quality bones, more easily exposed to bone breaking activities, then all we have is association of incorrectly understood markers of bone dynamics.

Similarly, the elderly population is also at increased risk. If we see no difference on a KD then I would consider it safe and a non-issue.

Attacks

Now that we have a little better understanding, returning back to the first paper. The next picture summarizes their conclusions.

CTX is related to collagen while osteoclasts are directly active in the breakdown process. Yet osteoclasts see a drastic reduction. In the diseased states such as CKD and T2D we saw increased osteoclast activity. We saw higher CTX activity in the young versus old population.

So the KD seems to resemble the young and healthy bone dynamics rather than a detrimental one. A stark contradiction in conclusion while the data remains the same.

For CTX we don’t really see any meaningful difference except right after exercise.

Rather than concluding impaired bone health, I would rather raise questions on the understanding of CTX. Especially when CTX and osteoclasts should be in agreement but here are opposite to each other.

Wikipedia is clear about this:

The CTX test measures for the presence and concentration of a crosslink peptide sequence of type I collagen, found, among other tissues, in bone. This specific peptide sequence relates to bone turnover because it is the portion that is cleaved by osteoclasts during bone resorption, and its serum levels are therefore proportional to osteoclastic activity at the time the blood sample is drawn.
source: https://en.wikipedia.org/wiki/C-terminal_telopeptide

P1NP may be in line with reduced osteoclast assuming you don’t need as much buildup when the breakdown is reduced.

Furthermore, the study was done short-term (3-3.5 weeks) while we’ve seen a study of 12 weeks showing no negative effect when just looking at BMD.

In other words, shortsighted conclusions .

Food for thought but fear of impaired bone health on a ketogenic diet is not something I’m concerned about. Until further better quality studies paint a different picture.

—- T H E – E N D —-

The intimate triad glycogen – lactate – beta-hydroxybutyrate

There is a close relationship between glycogen, lactate and beta-hydroxybutyrate (BHB) that I would like to highlight in this post. Although it looks like a simple relationship, it has important implications. There is more to cover but I’ll focus on the acute phase.

The essence

A first scenario, no matter the available fuel type (fat, glucose) in the circulation and at whatever ratio, glycogen contributes to the metabolism. I’m referring here to glycogen in all cell types, not just the liver or skeletal muscle cells. Glycogen in a cell is a buffer and a measure of available energy. When energy demand is higher than the rate at which glycogen can be build up, we get a declining level of glycogen. Very simple.

In such a way it is a measure of energy supply from the circulation. Increasing glycogen means sufficiency in circulation and declining glycogen the opposite. With declining levels at some point the situation becomes critical. How do you change the situation? How can a cell signal that it requires more energy?

As the glycogen level gets depleted..

It first of all reduces the contribution of the glycogen to metabolism.
It increases lactate production

Point 1 seems contradictory, we need energy so why reduce the contribution from an energy source? If the fuel in circulation is inadequate and glycogen level is low, the cell will dial down the activity to match what is available from the circulation to save as much of the remaining glycogen as possible. It simply cannot afford full depletion. It will use the glycogen for point 2 to attract more energy from outside the cell.

A second scenario, very similar to the first case but a different trigger, is hypoxia. When not enough oxygen is available, the mitochondria will be impaired in providing the necessary ATP. This also increases lactate production. It is something we know from cancer cells but is not uniquely attributable to cancer cells.

Common to both scenarios, the cell is in trouble for sufficient ATP production. So how can a cell rescue itself? There are a few tricks to rescue itself.

I suspect lactate increases GLUT1 expression so it can try and increase glucose supply to continue its glycolysis but still, this produces a low level of ATP versus what the mitochondria are capable of (yet faster production method).

Increasing lactate in the cytosol also increases monocarboxylic transporter 1 (MCT1) membrane expression. It does this to get rid of the lactate because it brings down the pH, but by doing so it opens the gates through which BHB can enter the cell.

BHB can get processed in the mitochondria and will generate more ATP while not requiring oxygen. So whatever the cause (low glycogen or hypoxia) it can provide more energy in a situation where there is a shortage in energy.

Once the lactate is out of the cell, we are not finished yet. It has to get into the blood circulation and we need to get BHB from the circulation into the cells. Endothelial cells need to get both substances across using the same transporters.

How this happens is not clear. A cytosolic increase in lactate increases the MCT1 expression but now we are outside of the cells. How do we get the endothelial layer to increase locally its MCT1 expression?

I wonder if this is a potential reason for why red blood cells have no mitochondria. They can only process glucose anaerobically so they are a constant source of lactate in the blood. Perhaps they keep the endothelial cells ready (since birth!) for cases where a local rise in lactate may emerge?

We also see the brain producing an excess amount of lactate making it export lactate at rest. Why wouldn’t it absorb all? After all it has a high need for energy and it can metabolize lactate without a problem. How important is it to ‘prime’ the system for adapting to shifts in metabolic substrates throughout the body? During exercise we see the flow of lactate reversed from circulation to the brain.

Is it comparable to a throttling car? It is much easier to start driving when already throttling compared to a cold engine that is not running at all.

References

“Monocarboxylate Transporter 1 Deficiency and Ketone Utilization” https://www.nejm.org/doi/full/10.1056/NEJMoa1407778

“The energy-less red blood cell is lost: erythrocyte enzyme abnormalities of glycolysis” https://ashpublications.org/blood/article/106/13/4034/133232/The-energy-less-red-blood-cell-is-lost-erythrocyte

“Long-Term Glucose Starvation Induces Inflammatory Responses and Phenotype Switch in Primary Cortical Rat Astrocytes” https://link.springer.com/article/10.1007/s12031-021-01800-2

In the next part I’ll go a bit more in depth and show what implications it has in practice.

Mechanisms

Glucose metabolism

Lactate is produced in cells through glycolysis. In the cytosol, glucose gets broken down to pyruvate. Pyruvate gets broken down further to lactate (referring to it as cytosolic glycolysis (cGY)). But for the majority of pyruvate is imported in the mitochondria where it is further converted to acetyl-CoA and processed in the TCA to produce much more ATP (mitochondrial glycolysis (mGY)). So only cGY produces lactate.

Response to lactate

Important to know is that MCT1 (and MCT4) can be quickly upregulated. Especially during exercise this is needed but also during acute issues in metabolism. Lactate is an acid and would lower the pH of the cytosol while this needs to be kept in balance. The lower the pH, the more spontaneous reactions happen while it has to be kept under control.

“Exercise rapidly increases expression of the monocarboxylate transporters MCT1 and MCT4 in rat muscle” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1665342/

GLUT1 expression

As mentioned earlier, lactate may increase GLUT1 expression which seems like a logical consequence. Under stimulation of hypoglycemia, the blood-brain-barrier increases GLUT1 concentration to increase glucose uptake. It needs a signal to do this.

“Blood-brain barrier glucose transporter: effects of hypo- and hyperglycemia revisited” https://pubmed.ncbi.nlm.nih.gov/9886075/

“Chronic hypoglycemia increases brain glucose transport” https://pubmed.ncbi.nlm.nih.gov/3532819/

During exhaustive exercise, the rat brain has upregulated GLUT1 in the cortex.

“Astrocytic glycogen-derived lactate fuels the brain during exhaustive exercise to maintain endurance capacity” https://www.pnas.org/content/114/24/6358

Cells that experience hypoxia upregulate GLUT1 expression as we can observe in cancer cells. Hypoxia itself is directly responsible for this.

“Hypoxia and Mitochondrial Inhibitors Regulate Expression of Glucose Transporter-1 via Distinct Cis-acting Sequences” https://www.sciencedirect.com/science/article/pii/S0021925818877146

Rats that are put on a ketogenic diet have an increased brain uptake of glucose (and acetoacetate). They found a 2-fold upregulation of MCT1 yet no increase in GLUT1 in the following study.

“Mild experimental ketosis increases brain uptake of 11C-acetoacetate and 18F-fluorodeoxyglucose: a dual-tracer PET imaging study in rats” https://pubmed.ncbi.nlm.nih.gov/21605500/

So it remains to be seen if GLUT1 upregulation is only due to hypoxia or if it can be done by lactate itself but perhaps requires a certain minimum dosage. A last paper on this topic did note an increase in GLUT1 expression in all cases when testing glucose deprivation and hypoxia separately and combined.

r/ketoscience - Keto increases the ability to receive glucose in the brain?

“Glucose deprivation and hypoxia increase the expression of the GLUT1 glucose transporter via a specific mRNA cis-acting regulatory element” https://onlinelibrary.wiley.com/doi/pdfdirect/10.1046/j.0022-3042.2001.00756.x

Again, we see an adaptation when cellular ATP production is impaired, the cell tries to increase influx of substrates that do not require oxygen to produce ATP. Glucose, lactate, BHB fit that job. ATP shortage needs to be fixed acutely.

Glucose sparing

Once BHB can enter the cell, it helps to save glucose usage. We see this for example in CD8+ T-cells where it helps them build up a glycogen buffer.

“Ketogenesis-generated β-hydroxybutyrate is an epigenetic regulator of CD8 + T-cell memory development” https://pubmed.ncbi.nlm.nih.gov/31871320/

A test in mice muscle showed a statistical effect as of 4mmol/L BHB post-exercise. They have a fast metabolism so potentially require higher levels versus humans.

“Effects of β-hydroxybutyrate treatment on glycogen repletion and its related signaling cascades in epitrochlearis muscle during 120 min of postexercise recovery” https://cdnsciencepub.com/doi/10.1139/apnm-2018-0860

Metabolic emergencies

When ATP supply is in danger, it is a metabolic emergency. We see this reflected in a couple of situations.

The failing heart

Different papers have come out showing increased ketogenesis and/or support from ketones under conditions of a failing heart.

“Ketone bodies for the failing heart: fuels that can fix the engine?” https://pubmed.ncbi.nlm.nih.gov/34456121/ – “Cardiovascular Effects of Treatment With the Ketone Body 3-Hydroxybutyrate in Chronic Heart Failure Patients” https://www.ahajournals.org/doi/10.1161/CIRCULATIONAHA.118.036459 – “Ketone therapy for heart failure: current evidence for clinical use” https://academic.oup.com/cardiovascres/advance-article-abstract/doi/10.1093/cvr/cvab068/6168424 – “Blood ketone bodies in congestive heart failure” https://pubmed.ncbi.nlm.nih.gov/8772754/ – “The failing heart utilizes 3-hydroxybutyrate as a metabolic stress defense” https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC6478419/ – “Nutritional modulation of heart failure in mitochondrial pyruvate carrier–deficient mice” https://www.nature.com/articles/s42255-020-00296-1

Different scenarios for failure exist but animal models show a reduction in fatty acid utilization.

“Beta-Hydroxybutyrate, Friend or Foe for Stressed Hearts” https://www.frontiersin.org/articles/10.3389/fragi.2021.681513/full

Acute heart failure is presented with increased lactate. I would guess the source of lactate is from the heart but with a failing heart, hypoperfusion could lead to systemic lower oxygen which would affect all cells in the body. In this paper they noted the increase in lactate without hypoperfusion.

“Increased blood lactate is prevalent and identifies poor prognosis in patients with acute heart failure without overt peripheral hypoperfusion” https://pubmed.ncbi.nlm.nih.gov/29431284/

It is guess work until I find better evidence but my thought is that the shift away from fatty acid oxidation will result in a higher lactate production to make use of the triad to bring in BHB. What is wrong with the heart that it cannot utilize fatty acids though? Or is it a deliberate shift?

Hypoxia

Just on a side note, lactate production, in response to hypoxia, stimulates angiogenesis. A neat way to prevent future hypoxic events. Lactate has many different roles, we’ve come a long way from seeing it as purely a waste product to how we know it today.

“A lactate-induced response to hypoxia” https://pubmed.ncbi.nlm.nih.gov/25892225/

When mice were stressed under hypoxic conditions they could see an improved tolerance. They had to combine iv glucagon and BHB because each alone did not improve tolerance. This is when they wanted to mimic the improved tolerance that is observed under fasting conditions under which glucagon and BHB are increased.

“Hypoxic tolerance enhanced by beta-hydroxybutyrate-glucagon in the mouse” https://pubmed.ncbi.nlm.nih.gov/6775395/

Further study of squirrels and rats indicate survival time linked to the level of BHB reached in the blood.

“Beta-hydroxybutyrate and response to hypoxia in the ground squirrel, Spermophilus tridecimlineatus” https://pubmed.ncbi.nlm.nih.gov/2364670/

In the following paper, the observed a lower circulating lactate level under hypoxic conditions (4.7 mmol vs 6.1 mmol) when comparing the KD with standard (high-carb) in rats, showcasing the ATP that is derived from ketones as a rescue of the metabolic emergency.

“Adaptation to Chronic Hypoxia During Diet-Induced Ketosis” https://link.springer.com/chapter/10.1007/0-387-26206-7_8

An other test on humans was performed to see how cognitive impairment is impacted by acute hypoxia, specifically due to reduced ATP production. A ketone ester (exogenous ketones) restored cognitive performance.

“A Metabolic Intervention for Improving Human Cognitive Performance During Hypoxia” https://doi.org/10.3357/AMHP.5767.2021

Non-alcoholic fatty liver (NAFLD)

Hepatic insulin resistance is part of NAFLD. Knowing that glycogen synthesis requires insulin, it should not be a surprise to observe higher lactate production by the liver due to lack of glycogen buildup.

In the following study in NALFD patients the hepatic lactate production was even higher before a KD diet. The KD diet resolves insulin resistance so we can expect glycogen to build up in these NAFLD patients but not much. A KD still requires low glycogen levels so the liver remains a source of lactate production.

“Effect of a ketogenic diet on hepatic steatosis and hepatic mitochondrial metabolism in nonalcoholic fatty liver disease” https://www.pnas.org/content/117/13/7347

Ketogenic diet

Under normal circumstances, the brain is already producing lactate in surplus so that there is an efflux from the brain to the blood circulation.

“Lactate transport and signaling in the brain: potential therapeutic targets and roles in body–brain interaction” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4426752/

“Striking differences in glucose and lactate levels between brain extracellular fluid and plasma in conscious human subjects: effects of hyperglycemia and hypoglycemia” https://pubmed.ncbi.nlm.nih.gov/11891432/

Under a ketogenic diet we generally see a reduction in glucose roughly as of >= 1mmol/L BHB (anecdotal observation). The brain can’t rely on fatty acids from the circulation so it would end up in energy starvation. On top of that, the skeletal muscle also needs to deal with the reduced glucose availability.

As we have seen above, this would start to deplete the glycogen in the cells so you get an increase in lactate production.

If the skeletal muscle would do this then it would also absorb the BHB that the brain is in need for. Instead, a ketogenic diet increases fat utilization in the skeletal muscle. This reduces the glycolytic action on glucose and thereby reduces lactate production so that it lowers MCT1 expression and lowers uptake of BHB.

The brain however, lowered in glucose affecting glycogen, does increase lactate production so that it can increase BHB uptake.

So everything balances out nicely.

The liver

NADH accumulation from beta-oxidation interferes with pyruvate formation. This essentially blocks gluconeogenesis from sources that require this step such as lactate.

NADH slows down the TCA so that acetyl-coa can pile up and can be used to form HMG-coa to push it further towards ketogenesis.

“Ethanol Alters Energy Metabolism in the Liver” https://www.ncbi.nlm.nih.gov/books/NBK22524/

Especially on a ketogenic diet, exercise will generate more free fatty acids that reach the liver. This is because exercise increases fatty acid release and heart rate causing a faster circulation.

Exercise (on a ketogenic diet)

I had a couple of max effort tests to check on my condition. This gave me the chance to compare lactate before and on a ketogenic diet. The grey line on the graph is on keto. At the early stage you can see how lactate is kept lower until 170 where it goes on par with the result from 2016 and as intensity goes up further, keto bypasses 2016.

Why am I showing this? During the first part, as intensity goes up, you see how lactate is kept lower thanks to relying more on fat but as intensity goes up further, reliance on glucose starts to increase. Because glucose in the circulation is lower, glycogen consumption now starts to increase at a higher rate. When we reach the highest intensity, on KD we are reaching lowest levels so most lactate production.

As you could read earlier, the brain needs the BHB and glucose. When we start exercising, lactate production goes up so the skeletal muscle will take up more BHB while also taking up glucose. That is a problem for the brain if it would not be compensated somehow.

The brain can also utilize lactate as a fuel. So we end up with a situation where the skeletal muscle exchanges lactate for BHB and the brain has to change BHB for lactate.

“Lactate transport and signaling in the brain: potential therapeutic targets and roles in body–brain interaction” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4426752/

This process is supported by the liver which reduces its lactate utilization for the gluconeogenesis (GNG) process. Instead it relies more heavily on glycerol for GNG which does not require the step to convert to pyruvate. This step is what is impacted under increased NADH availability. So we see that the liver is sparing lactate for the brain (and is itself even a source of lactate).

Glycogen utilization

A word on glycogen utilization though. It is assumed that on a KD, it spares muscle glycogen. I would argue yes and no.

A first element to take into account is that as glycogen levels start to decline, its utilization is slowed down. This is independent of diet.

A nice experiment was done by looking at glycogen utilization between 2 legs in the same subject. 1 leg started with reduced glycogen while the other leg didn’t. They observed a 60% reduction from glycogen in the ‘reduced’ leg while it took up 30% more glucose. Because arterial supply was the same, this effect could be fully attributed to the glycogen level.

“Effect of muscle glycogen on glucose, lactate and amino acid metabolism during exercise and recovery in human subjects” https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC2269057/

A paper from Timothy D. Noakes et all. also shows this reduced utilization. This could be wrongly interpreted as a glycogen-sparing effect of the ketogenic diet but note the lower level of glycogen that the KD group started with.

“Gluconeogenesis during endurance exercise in cyclists habituated to a long-term low carbohydrate high-fat diet” https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1113/JP271934

In contrast, a paper from Jeff Volek et all. shows equal utilization. This could incorrectly be interpreted as that there is no glycogen-sparing effect from the KD.

“Metabolic characteristics of keto-adapted ultra-endurance runners” https://www.metabolismjournal.com/article/S0026-0495(15)00334-0/fulltext

What should be taken into account is the intensity at which ATP needs to be generated. When intensity goes up but mitochondrial ATP production is covering the majority requirement then glycogen utilization will be equal among diets.

However, when intensity goes up mitochondrial ATP will not be sufficient. This is where fat metabolism and glucose metabolism make a difference. Glucose metabolism via mitochondria can be sustained at higher levels although yielding lower ATP amounts compared to fatty acids.

The result is that at very high intensities, glycogen will deplete faster on low carb. Circulating BHB will balance out this situation providing an alternative substrate for the TCA to increase mitochondrial ATP production.

Either BHB or medium chain fatty acids (MCFA) are able to support this action. MCFAs are not impaired for import like LCFAs are.

So does a KD help save muscle glycogen? There is no saving effect at low- to medium-intensity but at high-intensity BHB (and MCFA) do fulfil that role. That is, out of necessity. It doesn’t save glycogen more than high-carb but this is where optimization can help via exogenous ketones or MCT oil.

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The speed of the TCA in the liver

In previous writings I have looked at the liver and also ketone production from different angles but now I want to zoom in a bit on the TCA cycle itself.

Previous related writings:

In order to accumulate sufficient substrate for ketogenesis, acetyl-coa has to accumulate. The TCA cycle depends on the supply of acetyl-coa which makes them compete for the same resource. So how can this accumulation take place?

Below is a picture of the TCA cycle from wikipedia so that you can find back some of the elements mentioned further down.

Malonyl-coa interferes with long-chain fatty acid import into the mitochondria so with a reduction more fatty acids can get into those mitochondria. This is the location where fatty acids are processed to generate those acetyl-coa’s. On the other hand, increased malonyl-coa stimulates fatty acid synthesis. We want breakdown not buildup.

Malonyl-coa formation is dependent on glucose availability. On a ketogenic diet, in the liver cells we have a reduction in glucose. That allows for more AMPK activity which blocks the cytosolic conversion of acetyl-coa to malonyl-coa.

There are other aspects to take into account than just a reduction in malonyl-coa. This is where we need to have a look at the effects on the TCA cycle.

Oxaloacetate or oxaloacetic acid is reduced in supply. This is important because it forms a source for citrate production. Once transported out of the mitochondria, it pushes the conversion of cytosolic oxaloacetate to malonyl. This reaction consumes NADH. So under low glucose availability, we get an accumulation of NADH.

The production of ketone bodies is stimulated by the overproduction of acetyl-CoA (increased lipolysis and beta-oxidation) without concomitant production of an adequate amount of oxaloacetic acid (Paoli et al., 2015a). It is thus worthy to underline that the reduction of glucose flux, due to the nutritional carbohydrate restriction, leads to a lower level of oxaloacetate.
“Ketogenic Diet and Skeletal Muscle Hypertrophy: A Frenemy Relationship?” https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC6724590/

source: http://www.bioinfo.org.cn/book/biochemistry/chapt20/bio2.htm

What is important about NADH?

What we can learn from ethanol (alcohol) in the liver is that it also accumulates NADH. NADH reduces the activity of the enzymes isocitrate dehydrogenase and α-ketoglutarate dehydrogenase that take care of converting isocitrate to α-ketoglutarate and α-ketoglutarate to succinyl-coa in the TCA cycle. What we care about though is that both these enzymes produce NADH in the reaction. By NADH accumulation inhibiting these enzymes, it acts as a negative feedback-loop.

“Ethanol Alters Energy Metabolism in the Liver” https://www.ncbi.nlm.nih.gov/books/NBK22524/

Interestingly the accumulation of NADH also prevents oxidation of lactate and AA’s to pyruvate (part of gluconeogenesis (GNG)). Details are not provided here on how this mechanism works so consider that a little gap in proofing but I come back on this further down.

“Ethanol Alters Energy Metabolism in the Liver” https://www.ncbi.nlm.nih.gov/books/NBK22524/

However, malonyl in the cytosol is imported in the mitochondria where it undergoes conversion to oxaloacetate. This step generates NADH. Also pyruvate conversion to acetyl-coa produces NADH.

So on one side we see a reduction in production while on the other side we see a reduction in consumption. The question then remains, if and how does a KD increase NADH availability in the liver?

The answer may purely come from the beta-oxidation step. Shifting the balance to enhanced fatty acid import and breakdown in acetyl-coa we get increased NADH production with every cleavage.

This causes an accumulation, impacting the TCA cycle so that acetyl-coa are processed at a reduced rate. This causes the piling up of acetyl-coa so that ketone bodies can be formed.

Normally acetyl-coa accumulation stimulates fatty acid synthesis but because we are in a state of low insulin and high glucagon, in the liver this results in ketones.

In skeletal muscle cells this works out differently because they don’t produce ketones. There we see the increase of intracellular lipid droplets leading to local insulin resistance.

Knowing this, circulating BHB can be somewhat seen as a proxy for the speed of the TCA in your liver. Circulating levels are impacted by various other conditions but in general when you are at rest it will probably be a good reflection.

This is all driven by the availability of glucose in the liver cells. What does this mean for the liver though? If the TCA cycle is reduced, doesn’t that mean that ATP production is lowered in liver cells?

Each cycle of the TCA produces 1 ATP molecule and the whole mechanism also relies on AMPK activation. This indicates that the cells are in maintenance mode rather than growth which should be beneficial for liver health.

However, the beta-oxidation step itself produces 5 ATP for each acetyl-coa produced so producing ketones in the liver does not completely dry out the cell from its ATP.

Related to this beta-oxidation and NADH..

The formation of acetyl-coa also processes 4-HNE, a toxic lipid peroxide. This likely happens throughout the body where fatty acids are used, essentially working as a detoxification.

“Dietary-regulation of catabolic disposal of 4-hydroxynonenal analogs in rat liver” https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC3289253/ “4-hydroxynonenal in the pathogenesis and progression of human diseases” https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC3964795/

Coming back on the NADH accumulation and lactate as a source for GNG.. As we understand, under low glycogen levels shouldn’t that mean that the liver is also a source of lactate production?

The only study I could find that looked at liver lactate production in humans was one where they looked at NAFLD patients and put them on a 6-day KD diet. The lactate production from the liver was higher before than on the KD diet.

“Effect of a ketogenic diet on hepatic steatosis and hepatic mitochondrial metabolism in nonalcoholic fatty liver disease” https://www.pnas.org/content/117/13/7347

However, in NAFLD we have an insulin resistant liver skewing the results. Insulin drives glycogen formation in the liver so NAFLD may have glycogen levels that are even lower than on a KD diet. This actually supports the case even more for lactate production rather than consuming it for GNG purposes.

“Insulin Resistance and NAFLD: A Dangerous Liaison beyond the Genetics” https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC5575596/ “Lack of liver glycogen causes hepatic insulin resistance and steatosis in mice” https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC5481557/

NAFLD is closely linked with hepatic insulin resistance. Accumulation of hepatic diacylglycerol activates PKC-ε, impairing insulin receptor activation and insulin-stimulated glycogen synthesis.
“Nonalcoholic Fatty Liver Disease as a Nexus of Metabolic and Hepatic Diseases” https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC5762395/

Although it is a study in mice, the authors of the following study came to the same conclusions as to what I expect.

In parallel, it was observed that blood lactate level was enhanced whereas liver glycogen levels were reduced in mice perfused with BHB. Because G6Pase is common to gluconeogenesis and glycogenolysis, which classically leads to glucose release, it appears in our case that the observed glycogen breakdown would not lead to glucose release but rather to a glycolytic processing of glucose residues arising from glycogen. In other words, the observed glycogen degradation would lead to a hepatic lactate production, thus explaining the increased lactate level, reinforced by the decreased gluconeogenesis that would prevent hepatic lactate utilization and rather promote circulating lactate accumulation.
“Evidence for hypothalamic ketone body sensing: impact on food intake and peripheral metabolic responses in mice” https://journals.physiology.org/doi/full/10.1152/ajpendo.00282.2015

Finally

We can learn a lot from studying the liver but we have to keep in mind that results are liver-specific. Nevertheless, it has a key role in the energy metabolism regulation throughout our body. It is essentially an intersection point where a lot of decisions are taken.

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Metabolism on a ketogenic diet

Let me first clarify that this article is about a true ketogenic diet, meaning you actually produce higher levels of BHB. Why am I saying this? Because I notice quite a number of people who leave out most carbs but they don’t necessarily reach the ketogenic state due to various reasons. I’ve always said and will keep on repeating: Measure your blood BHB level to validate if you are in a ketogenic state.

That said, what is this article about? I had this idea for a while where I suspect that there is a reduction of metabolism on a ketogenic diet. This is noted by a drop in the thyroid hormone T3 and a rise in reverse T3 (inactive T3). Yet we notice a higher energy consumption which tells us that metabolism is higher. We also notice a higher heat production on a ketogenic diet. So the question is if this increase in heat production is of such magnitude that it covers both the increase versus a standard diet and the reduction in metabolism versus a standard diet.

This is not proportional, just for illustration purposes. Note though that scientifically it will be argued that heat production is part of the metabolism. I would argue it is part of energy loss but it is nor part of cell metabolism in the sense that it doesn’t contribute to metabolism. Rather it is a result of metabolism just like we produce water and CO2 which gets dissipated from our body.

The efficiency of the metabolism will determine how much heat is produced versus how much workable energy for the cell is produced in the form of ATP.

What I want to do next is look at evidence that shows if there is a lower metabolism yet a higher heat production but also at the numbers to get an estimation of how much more heat could be produced.

Before getting into the details, here is an article from Stephen Phinney, PhD (a highly respected low carb researcher) who argues for increased sensitivity to T3 because metabolism is maintained while recognizing the drop in T3. However I do not agree to this sensitivity hypothesis because as stated, I believe metabolism does go down yet the heat production goes up so that total energy consumption is maintained or even elevated.

So to recap…

Energy consumption is equal or increases
Energy production (metabolism; ATP production) decreases
Heat production (energy loss) increases

Lower T3

Phinney referred to unpublished data from Volek showing in a calorie restricted setting (estimated weight maintenance – 500 kcal) a drop from 4.2pmol/L to 3.5pmol/L, low-fat to KD for 14 overweight men. That is 17% lower.

“Comparison of energy-restricted very low-carbohydrate and low-fat diets on weight loss and body composition in overweight men and women” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC538279/

A second reference that he provided shows an iso-caloric comparison of 85%, 44% and 2% carbohydrates for 6 men during 11 days. The T3 levels measured were 1.78, 1.71 and 1.33 nmol/L. The 2% carb is 23% lower in T3 than the 44% carbs.

“Isocaloric carbohydrate deprivation induces protein catabolism despite a low T3-syndrome in healthy men” https://pubmed.ncbi.nlm.nih.gov/11167929/

1nmol = 1000 pmol so I think there is a mistake in units used. In any case, this second study already gives us an important indication. It seems that the level of carbohydrates in the diet determines the level of T3. Still, it could also be depending on the protein. Despite that this is kept equal in the diet, the drop in carbohydrates allows glucagon to be more active resulting in more gluconeogenesis which also catabolizes amino acids into glucose thus resulting in a lowering of the plasma amino acids.

The study noted an increase in urinary nitrogen excretion (10.91; 12.79; 15.89 g/24h). A 24% increase in protein catabolism. Please do note that switching to a ketogenic diet takes roughly 11 days for the body to adapt in order to reduce the protein catabolism. Search for “transition” on that page.

Insulin stimulates muscle protein synthesis (under sufficient leucine). By drastically lowering insulin this would make (muscle) protein more prone to catabolism unless there are counter measures. Lowering metabolism via T3 reduction, besides protection from BHB and growth hormone, is an essential element to reduce amino acid requirements in a cell that wants to build protein.

“Thyroid hormone stimulates protein synthesis in the cardiomyocyte by activating the Akt-mTOR and p70S6K pathways” https://pubmed.ncbi.nlm.nih.gov/16717100/

“Effect of T3-induced hyperthyroidism on mitochondrial and cytoplasmic protein synthesis rates in oxidative and glycolytic tissues in rats” https://journals.physiology.org/doi/full/10.1152/ajpendo.00397.2006

“T3 increases mitochondrial ATP production in oxidative muscle despite increased expression of UCP2 and -3” https://journals.physiology.org/doi/full/10.1152/ajpendo.2001.280.5.E761

We see that hypothyroidism results in a reduction of amino acid efflux from skeletal muscle and a reduction in protein synthesis in various tissues.

Amino acid release (alanine, glycine, tyrosine, glutamine) is increased in hyperthyroid skeletal muscle [9] while it is decreased in hypothyroidism [9, 15, 22].
…
in hypothyroidism hepatic synthesis of intracellular or secretory proteins is reduced by 20% and 50%, respectively [18, 40].
…
Total cellular protein toss during a starvation period is reduced by 50% in the hypothyroid state, mainly due to a decrease in the cytosolic compartment, while in hyperthyroidism there is no change [44]. In starvation, mobilization of hepatic proteins is decreased in the thyroid deficient state, providing a prolonged conservation [44]
source: “Thyroid hormone action on intermediary metabolism. Part III. Protein metabolism in hyper- and hypothyroidism” https://pubmed.ncbi.nlm.nih.gov/6231411/

What we have seen here is that T3 modulates (increase/decrease) the basal level of ATP production and mTORC1 stimulation affecting amino acid utilization for protein synthesis and replacement.

Circulating amino acids are measured and accordingly the body responds. Stimulate synthesis when there is abundance, conserve when there is shortage.

The ketone molecule BHB reduces protein catabolism but before we get to this point we first have to generate BHB and for that dietary protein has to be low enough in the first place. Note: I’m not saying “low” but “low enough”.

A study in healthy subjects where they put them on a 4-day ketogenic diet report what we have already seen. A drop in T3, rise in reverse T3. Interestingly they also looked at the amino acids. The gluconeogenic amino acids alanine, glutamine, glycine, serine and threonine were reduced by 8-34% while those of the branched chain amino acids increased by more than 50%.

“Hormonal and metabolic changes induced by an isocaloric isoproteinic ketogenic diet in healthy subjects” https://pubmed.ncbi.nlm.nih.gov/6761185/

An important note, circulating levels are always the result of production rate and consumption rate.

Increased UCP

UCP allows for the loss of electrons that dissipate as heat during metabolism. A higher level of UCP will mean that more heat will be generated and less ATP.

In the following rat study they gave a control diet, control+sucrose drink, low protein-high carb or low protein-high fat diet. The authors concluded the following:

Brown adipose tissue protein content and thermogenic capacity (assessed from purine nucleotide binding to isolated mitochondria) were greater than control values in sucrose-fed and protein-deficient animals, and the greatest levels of activity were seen in low protein–fed rats with a high fat intake.

Why greater in the high fat versus the high carb? Because dietary carbs result in a direct feed of glucose to the brain so there is more protection from catabolism due to the higher insulin stimulation. Dietary fat doesn’t stimulate insulin as much and in contrast requires the dissociation of the fatty acids from the glycerol backbone so that the glycerol can serve as a gluconeogenic source. But what to do with that abundance of free fatty acids? Get rid of them via thermogenesis. With a low protein-high fat diet you need a higher level of fat metabolism to get to an equal level of protection from amino acid catabolism.

The thermic effect seems to be double that from the control group.

The acute thermogenic response (% rise in oxygen consumption) to a standard balanced-nutrient meal was higher (12%) in sucrose-supplemented and in low protein groups (15-16%) than in control rats (8%).

“Influence of Carbohydrate and Fat Intake on Diet-Induced Thermogenesis and Brown Fat Activity in Rats Fed Low Protein Diets” https://academic.oup.com/jn/article-abstract/117/10/1721/4780321?redirectedFrom=fulltext

The next animal study gave the rats a ketogenic diet with 9% protein. Versus the control group they ate the same amount of calories, had reduced weight gain and generated 11% more heat. The 66% calorie restricted group had obtained a similar fat mass and lean mass composition but without the heat production.

“A high-fat, ketogenic diet induces a unique metabolic state in mice” https://journals.physiology.org/doi/full/10.1152/ajpendo.00717.2006

I do want to warn about animal studies though and caution with interpretation. 2 main issues could influence the results.

1) isocaloric feeding: if a low protein diet requires more fat burning then the ad lib feeding could result in a higher dietary intake. By giving the same calories as the control diet you reduce the protein catabolism protection. This may lead to a lower thermogenesis capacity than they would do naturally and at the same time have a reduction in growth.

source: “Isoenergetic Feeding of Low Carbohydrate-High Fat Diets Does Not Increase Brown Adipose Tissue Thermogenic Capacity in Rats” https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0038997

2) Too low protein: when feeding animals very low protein amounts or even absent protein, they will have a lower protein assembly capacity. In order to increase heat production, fat needs to be metabolized via an increase in UCP expression and at the same time the machinery for fat metabolism needs to be enhanced. This means proteins (carnitine) need to be assembled to form the necessary enzymes, hormones etc. If the level of circulating amino acids go too low then those protein assemblies could be under pressure as well.

When evaluating this in humans we see a similar result. Energy expenditure goes up when carbohydrates are exchanged for fat while keeping protein equal. The subjects on low carb had a TEE of 2713 kcal/d and this changed at the end with an increase of 270 kcal/d so roughly 10% which is in line with the animal study.

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“Effects of a low carbohydrate diet on energy expenditure during weight loss maintenance: randomized trial” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6233655/

Finally

So we see from the reduction in T3 that cell metabolism in general slows down while we see in skeletal muscle and brown adipose tissue that heat production goes up. Lean mass growth is slowed down.

What this essentially means is that the heat production increase is not just the additional energy expenditure that is observed, it also covers whatever the reduction is in metabolism. Keep in mind that 17~23% T3 reduction which by itself results in a lower heat production. The calorie-restricted mice had a 6% reduction in heat versus the control while the KD had an almost 8% increase in heat production versus control.

It all depends on the level of dietary protein and how it is combined with carbs or fat.

Longevity is associated by a low IGF-1 and T3 in those who live well above 90 years. As long as we can maintain or even build muscle strength, reducing protein and carb while increasing fat intake may be a good strategy to reduce overall tissue metabolism.

“Familial longevity is associated with decreased thyroid function” https://pubmed.ncbi.nlm.nih.gov/20739380/

The level of protein has a major role in signaling ideal reproduction times. Lowered levels indicate a less than optimal time with a need to be conservative.

On the menu you can choose:

with increased heat production (high fat)
without heat production (high carb)

The choice is yours.

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A ketogenic diet increases the brain glucose uptake mechanism

When looking into acetoacetone uptake by the brain, I bumped against the following article. I don’t have full access but the abstract showed me the following:

Similar trends were observed for (18)FDG uptake with a 1.9-2.6 times increase on the KD and F(asting), respectively (P < 0.05).

FDG -> radiolabeled glucose such as used to trace cancer. But more importantly, a good doubling of the uptake of glucose! So I started thinking, is it the case that our brain is sucking up so much glucose? Or is this just a side effect of being ketotic and getting a big bolus of glucose administered?

“Mild experimental ketosis increases brain uptake of 11C-acetoacetate and 18F-fluorodeoxyglucose: a dual-tracer PET imaging study in rats” https://pubmed.ncbi.nlm.nih.gov/21605500/

———————–

I find it interesting because astrocytes produce more lactate on starvation and I assume on keto as well. Why? To increase the expression of MCT1 transporters on the endothelial cells in the blood-brain-barrier which allows a higher uptake of BHB.

Pyruvate can otherwise be reduced to lactate by lactate dehydrogenase (LDH). This lactate can be released in the extracellular space through monocarboxylate transporters (MCTs).

“Brain Energy Metabolism: Focus on Astrocyte-Neuron Metabolic Cooperation” https://www.sciencedirect.com/science/article/pii/S1550413111004207

Astrocytes can store small amounts of glycogen which they, if necessary, break down to glucose and metabolize to lactate (Falkowska et al. 2015). To fulfill this functional characteristic, astrocytes are highly metabolically flexible and can rapidly upregulate glycolysis. In the event of an undersupply, astrocytes thus ensure the survival and function of neurons by providing lactate (Kasischke et al. 2004; Pellerin and Magistretti 1994).

“Long-Term Glucose Starvation Induces Inflammatory Responses and Phenotype Switch in Primary Cortical Rat Astrocytes” https://link.springer.com/article/10.1007/s12031-021-01800-2

———————–

So it seems that astrocytes start to increase lactate production when glucose is running low and they use their little glycogen buffers for that. Cool. So that coincides nicely with an increase in ketones and takes care of the BHB uptake, balancing out low glucose with increased BHB.

I guess it would make sense for the brain to increase its ability to take up glucose which is then indicated by the first link I provided. So I don’t think the brain is actually continuously taking up so much glucose, it is just that it has opened the gates to maximally receive glucose.

Further a reference that shows increased glucose uptake under chronic hypoglycemia

“Chronic hypoglycemia increases brain glucose transport” https://pubmed.ncbi.nlm.nih.gov/3532819/

A first candidate to look at what could cause that increase in uptake is the GLUT1 transporter. And indeed, the following article looked at GLUT1 expression in the BBB under glucose deprivation, hypoxia and the two combined.

Summary

astrocytes sense low glucose availability
astrocytes increase lactate production
lactate increases MCT1 expression
increased MCT1 enables more influx of BHB into the brain
low glucose increases GLUT1 expression in the BBB to maximally take up glucose

So this shows a whole balancing mechanism, it allows a shift from purely glucose to glucose and BHB.

———————–

For people who interpret this as ketones being a backup and think this is showing the brain needs glucose… I’d say the truth is somewhere in the middle 😉 Consider the following quote. There may be a point that can be crossed when too much glucose is available and can be considered toxic when that downregulates GLUT1 in the BBB to the point that the brain doesn’t get enough glucose. Also here the astrocytes may start to produce lactate but it won’t do any good because under hyperglycemia, there won’t be any BHB produced.

Glucose transport into the brain is depressed in chronically hyperglycemic (diabetic) rats.

“Chronic hypoglycemia increases brain glucose transport” https://pubmed.ncbi.nlm.nih.gov/3532819/

Compared with normal control rats, the GLUT(1) mRNA was reduced by 46.08%, 29.80%, 19.22% (P < 0.01) in DM1, DM2, and DM3 group, respectively; and the GLUT(3) mRNA was reduced by 75.00%, 46.75%, and 17.89% (P < 0.01) in DM1, DM2, and DM3 group, respectively.

“Influence of blood glucose on the expression of glucose trans-porter proteins 1 and 3 in the brain of diabetic rats” https://pubmed.ncbi.nlm.nih.gov/17935675/

But I find contrasting evidence. In the following article they noted no effect on GLUT1 expression. Different rat models so who knows what the case is for humans..

“Blood-brain barrier glucose transporter: effects of hypo- and hyperglycemia revisited” https://pubmed.ncbi.nlm.nih.gov/9886075/

Why is this important? We see reduced expression of GLUT1 in Alzheimer’s. Is it a genetic issue or not and can it be partially prevented or even reverted when going on a low carb diet? Food for thought…

“GLUT1 reductions exacerbate Alzheimer’s disease vasculoneuronal dysfunction and degeneration” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4734893/

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Insight into evolution

Where do we come from and where is it taking us?

Lately I’ve been exposed to different, seemingly unrelated pieces of information. However putting them all on the table, a pattern started to emerge. Join me in a philosophical trip making sense out of evolution and what it could possibly have in storage for us. To put a bit of structure in it, there’s the history, our present and the future.

The beginning

When we talk about evolution we talk about life. But what is life? The only element that is an absolute necessity is reproduction. If something cannot reproduce there is no lineage, there is no evolution. We just have static elements.

Life itself cannot exist at random. You cannot throw a bunch of molecules together and have reproduction. Reproduction is the result of an organization of molecules in such a way that they together not only produce something but actually replicate itself. Such an organization doesn’t come easy. In fact, it has taken a good 1,5 billion years before we saw the rise of the first single-cell life before the right match was found.

And that wasn’t the end of the story naturally. Reproduction requires resources, raw material. Putting things together requires energy. Reproduction thus depends on raw material and energy. As such, life is confronted with another problem. If you just allow unrestricted reproduction, how are you going to obtain that material and energy?

Maybe the material and energy is floating around you but a little bit to far and you miss it so life had to develop the ability to move. If you look at such examples today, you’ll see single-cell life with moving parts. Movement costs energy.

But where do we move to? Just move around? It is going to be hit or miss to find material and energy. We certainly don’t want to be moving out of an environment that is ideal for reproduction. So evolutionary pressure requires the development of environmental sensors, a sense of direction so that the single cell life form can position itself in a more ideal location for reproduction.

The elements that are required for reproduction are not always abundant everywhere. There’s also the problem of competition. As a cell is able to reproduce, more and more start to exist. They all want to reproduce so they compete with each other for the resources. This will create scarcity of resources and life will cease to exist.

Again, evolution comes up with a solution. Cells start to lower their needs when there is a lack of resources. They start to differentiate in state. Grow when there is abundance and wait for more ideal times by reducing requirements.

We are now again millions away from our first reproduction moment and still are primarily focusing on successful reproduction. It doesn’t stop here and will actually never stop.

One more last step before we’ll do a fast forward. As a single cell we have developed a good set of capabilities to succeed in reproduction. Curiously though, cells evolved further. It seems to be beneficial to work together rather than compete against each other. When cells group together and in agreement with each other allow for specialization, the group as a whole develops capabilities that are not possible for an individual cell.

That is interesting, just as the molecules had to come together in the right formation to create the capability to reproduce, now cells do it at their level. Just as the many molecules are different from each other providing a piece of the functionality, so do the cells when they start to work together. They start to differentiate and contribute specific functionality of which the group will benefit. Benefit in what way? Again, improve their ability to reproduce.

A brain, skeleton and muscle are the pinnacle that allows movement, detection, observation etc.. to get the cooperation of cells, that now have formed a body, in a more liberal way to the resources that it so desperately needs to reproduce.

Our more recent history

Fast forwarding now. Evolution has developed many different life forms. They all specialize to ensure reproduction in their living environment.

We’re in the era where Neanderthals are roaming around the world. They managed to survive for a good 400K. Much longer than we as modern humans have been around yet look at what we have done in a much shorter time span.

If you think brain size reflects intelligence, you’ll be disappointed. They had a similar size, if not even bigger. Our own brains have in fact reduced in size since the introduction of agriculture. Never mind brain size, let’s look at what is being done with that brain.

We see that modern humans developed art work and evolved in tools, hunting techniques. Neanderthals did not. We suspect they were able to imitate and have some evidence of that at the point where Neanderthals encountered modern humans. Modern humans did not exterminate the Neanderthals as the interbreeding seems to suggest.

The different elements I’ve read about seem to suggest to me that Neanderthals were missing a creative element. Creativity is an important requirement to resolve problems. It also allows you to explore, discover, run through scenarios, imagine things that do not exist.

There are theories that indicate modern humans have hunted the large mammals to extinction. How would Neanderthals survive in such a situation? Switch over to hunting smaller game? They would have had to adapt their tools, strategies, update their learnings, techniques etc.. and we see no evidence of that.

The fractures of their bones indicate their hunting technique made use of close encounters with their prey. When we look at wild life, the predators are using their own body as weapons. Modern humans, thanks to that creativity I’m guessing, have moved beyond that. Another success story for increasing the chance of reproduction.

Just as cells were at some point in competition with each other for resources, so may Neanderthals and modern humans have been. Again a natural selection of a feature that improves the ability to reproduce has been selected for.

Creativity is not something that emerged from our encounter with Neanderthals though. We already had it when we came out of Africa. Our evolution suggests that we evolved alongside large mammals in Africa. Hunter and prey co-evolved in a way that sparked the development of creativity to overcome problems in obtaining prey.

Modern days

Another fast forward and we are today. What evolution did to molecules to for a cell, what evolution did to cells to form a body, so does evolution continue and created groups out of those bodies. As humans we have formed groups in many different forms but the same rules continue to apply. The group is the next level of cooperation.

Throughout our history, evolution has experimented with many different groups in many different ways and locations. Societies have risen and fallen. These groups were not able to sustain themselves long enough. Communities emerged and disappeared. The group was not able to secure food and energy to continue reproduction.

What we can see around us today is the latest most successful form.

The bodies (us) specialize to support the existence of the group. Some are specialized at growing food. Some specialize at generating energy. This specialization is freeing up time for others to specialize in their respective area, all for the benefit of the group existence. We have scientists who use their creativity and intelligence to discover how things are working. We have engineers who take those discoveries and combine it with their own creativity to come up with new applications. The group has enabled bodies to specialize in repairing damaged bodies etc.. All these bodies depend on the specialization of the others.

As we’ve seen, layer after layer new capabilities start to emerge. What are those group capabilities. As a group we first of all protect the survival of the group because now we have moved reproduction up to the level of the group. We are currently worrying about climate change. The group has advanced enough to overcome this problem. Either that or the group will disappear.

Currently our focus is to secure our energy need as a group. We started out with burning wood, then charcoal. Then we invented electricity and use charcoal, wind, water etc for it but our energy need continues to grow and we know the resources to produce that energy are finite.

Thanks to the group, that problem is being addressed by bringing solar fusion within the reach of the group. There are several initiatives to create a sustained hydrogen fusion reactor which will deliver more energy than the amount that is needed to keep it running.

More incredible group stuff is happening. We are actually preparing a trip to Mars. We are upscaling our knowledge of everything at an immense rate. What we can discover, know, build… as a group far exceeds what can be done by an individual body.

The capabilities of the group is however determined by the capabilities of the layer beneath. What the group is doing is going through another level of selective pressure to favor intelligence in the bodies that make up the group.

Some people may not like this from a moral or ethical point of view but intelligence is being rewarded more than anything else in our current groups. It is not a matter of fairness, it is a necessity. The group needs to survive. Just as a single cell was floating around and had to adapt, so does the group. Raw material and energy remain limited.

The group needs to develop methods now to become more efficient to reduce the need for raw material. And we are doing that by continuously improving the scale of our devices and tools. I’ve already pointed out to securing energy via the fusion reactor. More and more is the group in need of bodies who can come up with solutions that enhance the survivability of the group and when possible allow it to reproduce.

Intelligence is selected for in favor of raw muscle power. Intelligence is more important and can overcome the lack of muscle power by inventing robots which will replace the shortcomings of diminished muscle power.

Future

This group level existence allows me to have a positive outlook. As each next level in evolution shows us that cooperation rather than competition is the best way forward, we can expect war, tribalism, religion, country borders.. whatever we have done in the past to separate us from others will disappear as it doesn’t help the group to advance.

Our current group configuration may not be the final last form but it may evolve, through trial and error, to the most optimal form to sustain reproduction because that is what life is about.

The group will have specialized in preservation, in creating a sustainable eco-system for the group. It will have specialized in mastering the vast amount of energy that is available in the universe. The group will know intrinsically that cooperation is the way forward.

With such lessons learned we will move out into outer space.

How will we look like when we evolved our intelligence to a high enough level? In order to have a brain that can improve the way we think we actually may need more volume. I’ve discussed before with the Neanderthals that brain size is not necessarily related to intelligence but that is as an absolute parameter.

There is however a rule in life that requires a balance within the organs. In our own evolution, our gut size had to shrink to allow a bigger brain. The brain is very energy hungry so growing a bigger brain means that something else has to reduce consumption. This may lead us to optimize food intake further, shrinking more of the gut or some other solution like reducing our muscle mass which we can only afford if our brain can compensate the lack of muscle. We can afford a reduction in muscle if we have a smaller skeleton.

Does that sound familiar? A big head and skinny body? Maybe you are laughing now but realize that I’ve not stated anything unreasonable 😉

Keeping in mind those lessons learned and understanding how we evolved, how would we travel through space? As hungry pirates completely stripping every planet of the resources that we can use or do you think it is more closely to something like Star Trek where we just observe.

Putting the science fiction aside for a minute. I see us supporting development of other life forms with a minimal interference. Self-development with a little kick in the right direction if you will and from time to time come back and see how it is going. Just like we do lab research. Probably we’ll make some errors at this level as wel but over time will improve. We will inspect other planets other galaxies out of curiosity just to see what is out there and if we can further improve our understanding.

As a group we will seek cooperation with other groups if we find any so that we can get to the next level. From molecules to cells to bodies to groups to whatever comes next.

Does that sound like a plausible future? Could it then be feasible that life on an other planet already got to this point and kicked us in the right direction?

Back to the present

I’m fascinated by Göbekli Tepe. This place has been dated around 11 500 before present. It is an enormous structure of which only a small portion has been excavated. What makes it so special is that, following our modern day thinking, there are some elements that don’t really seem to fit. For example, given the size there must have been a huge organization to get everything in place. This requires a society of workers, others who provide food for the workers. You need local storage facilities, some form of containers for water and so on. No signs of any of that.

We can see an evolution of tools and buildings throughout history, yet for this location none of that. It just seems to have popped into existence.

So I let my imagination mix in with the future outlook I just described earlier. What if there was life on another planet that gave us that kick in the right direction? What if that kick was to put a monument? How would we respond to it with our creativity, curiosity and intelligence?

We would gather around it, not understanding what it is. Inspect it and start using our creativity. These blocks of stone are huge. A small person like ourselves cannot lift these stones so whoever did it must have been huge and strong, very powerful. Who are they? Maybe this has led us to the concept of gods. Where are they? Maybe they’ll come back so we’ll come back as well to meet them.

It becomes a meeting place where people exchange their ideas. Because it is a unique reference point, unique like we need them to navigate the landscape and remember our routes, routes establish themselves to and from the monument. Trading and exchange of goods increases. A few individuals start to settle locally to support the trade and local needs. Whoever travelled from far away may be hungry when they get to this point so we feed them.

Some of those grains collected by the gatherers falls on the ground unnoticed but due to increased return they notice the same plants as those that they got the grains from elsewhere. And the rest is history..

Finally

Reproduction is at the core of life, evolution is the result of a cooperation to improve the outcome of a common goal. With every new layer of cooperation, capabilities emerge that were not possible before, further securing reproduction and thereby sustaining life.

How will life be for us in a few thousand years from now? I bet we’ll still play by the same rules 😉

—– T H E – E N D —–

CETP

Read it carefully as it may help you assess your risk for cardiovascular disease!

In my previous article comparing pathological versus physiological high LDL-C levels, one of the marked differences is that HDL-C goes down under the pathological situation versus up on the physiological case.

This difference comes down to cholesterol ester transfer protein or CETP. That has triggered my curiosity so naturally I wanted to understand more of it.

What does it do? Where does it come from? And since we see our HDL-C levels modulated by diet due to this CETP activity.. how does diet modulate CETP?

Exchanger

First, what does it do? CETP is responsible for the exchange of triglycerides for cholesterol between the lipid particles. HDL-particles will give up a cholesterol ester in exchange for a triglyceride from ApoB-containing particles such as VLDL, IDL or LDL.

What normally happens is that the HDL-particle gets loaded up with triglycerides. The liver will take up triglyceride rich HDL-particles via hepatic lipase. Stripped from its triglycerides, the remnant HDL is put back into circulation but risks higher clearance via the kidneys.

“New insights into the mechanism of low high-density lipoprotein cholesterol in obesity – Changes in HDL component” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3207906/#__sec6title

This explains why we see HDL-C trend upwards for athletes and lean individuals on a ketogenic diet. It is due to their CETP activity being reduced.

But it raises a question. It could explain why LDL particles become large buoyant in size as the particle is not unloading its triglycerides to the HDL particle. But the HDL particle normally also exchanges with VLDL particles so how come the lipid profile results in low triglyceride levels under reduced CETP activity?

This may be difficult to answer but could be driven by a reduction in VLDL-sized ApoB particles. Under fasted conditions, the liver may be producing LDL-sized ApoB particles directly which is true under prolonged fasted conditions where the liver is more tuned towards fat metabolism.

Macrophages

Low CETP activity induces higher cholesterol efflux from macrophages to HDL-particles. When we look at subjects with homozygous CETP deficiency we see a 2~3-fold increase in efflux.

“HDL from CETP-deficient subjects shows enhanced ability to promote cholesterol efflux from macrophages in an apoE- and ABCG1-dependent pathway” https://pubmed.ncbi.nlm.nih.gov/16670775/

But we are not all genetically deficient in CETP. When using a drug that inhibits CETP activity, we also not a higher efflux capacity.

“Cholesterol Efflux Potential and Anti-inflammatory Properties of HDL following Treatment with Niacin or Anacetrapib” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2917780/

Metabolic syndrome

Given that lower CETP activity is beneficial as it increases HDL-C and causes a greater efflux of cholesterol from macrophages, we want to know what the level is for ourselves.

HDL-C by itself is already a good proxy but the following study shows that CETP activity is also associated with increased BMI, fasting glucose and c-peptide. This explains why obese people tend to have lower HDL-C

“Effect of adiposity on plasma lipid transfer protein activities: a possible link between insulin resistance and high density lipoprotein metabolism” https://pubmed.ncbi.nlm.nih.gov/8033953/

When reviewing patients with metabolic syndrome, they found increased CETP activity (and PCSK9).

“Circulating PCSK9 levels and CETP plasma activity are independently associated in patients with metabolic diseases” https://cardiab.biomedcentral.com/articles/10.1186/s12933-016-0428-z

Small dense LDL

In type 2 diabetes patients it has been demonstrated that CETP contributes significantly to the increased levels of small dense LDL by preferential CE transfer from HDL to small dense LDL, as well as through an indirect mechanism involving enhanced CE transfer from HDL to VLDL-1(114). … Recent evidence has indicated that a primary acceptor for CETP-mediated HDL cholesteryl ester transfer in normolipidemic subjects is a large, buoyant, triglyceride-enriched LDL subclass (116).
source: “Metabolic origins and clinical significance of LDL heterogeneity” https://www.sciencedirect.com/science/article/pii/S0022227520328005

CETP targets the large buoyant LDL particles and turns them into small dense LDL particles. Small dense LDL is a biomarker for atherosclerosis.

Here are some numbers from a study looking at events across 2 years in people with metabolic syndrome. In those with events: LDL size was lower (P < 0.0001), due to reduced larger subclasses and increased small, dense LDL (all P < 0.0001). After multivariate analysis for independent risk factors: elevated small, dense LDL (OR 11.7, P = 0.0004). Now that is impressive.

“Small Dense Low-Density Lipoprotein as Biomarker for Atherosclerotic Diseases” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5441126/

“Small, dense low-density lipoproteins (LDL) are predictors of cardio- and cerebro-vascular events in subjects with the metabolic syndrome” https://pubmed.ncbi.nlm.nih.gov/18771560/

Insight

If you paid close attention to the above then you may have noticed something.

HDL-particles have 2 jobs. Doing one makes it bad at the other and this is regulated by CETP activity.

Recycling of triglycerides from LDL-particles to the liver
Taking up cholesterol from macrophages

When CETP activity is high, HDL volume reduces from circulation because it is taken up by the liver (and also by the kidneys). With less of them available, there is less availability to take up cholesterol from macrophages.

When CETP is low, there is greater capacity to take up cholesterol from macrophages. As a result LDL particles will have to hold on to their triglycerides more.

CETP activator

So what causes CETP to be activated or turned down?

CETP is secreted by the liver and this is regulated by liver x protein (LXP). Higher stimulation of LXP causes higher levels of CETP.

Interestingly higher LXP also causes a higher stimulation of GLUT5 expression in the duodenum and adipose tissue.

“Identification of the fructose transporter GLUT5 (SLC2A5) as a novel target of nuclear receptor LXR” https://www.nature.com/articles/s41598-019-45803-x

The duodenum is particularly interesting because it is thought that most of the fructose is processed by the bacteria in the small intestine. This idea is based on the following study which, to my view, people incorrectly extrapolate to humans. The study was done in mice and I doubt they have a similar gut microbiome. Secondly fructose that would be absorbed by the liver and converted to fat would not immediately show up in the circulation.

“The Small Intestine Converts Dietary Fructose into Glucose and Organic Acids” https://www.sciencedirect.com/science/article/pii/S1550413117307295

It is important to find out what causes higher expression of LXP. Causing more fructose to be absorbed into the body is really not a good thing. It already creates a bad lipid profile for cardiovascular disease.

LXP activity

I figured it had something to do with fat metabolism since we see evidence of very low CETP activity in very lean individuals on a ketogenic diet. The diet features things such as PPAR-alpha increase, PGC-1alpha increase, AMPK increase. So a quick look around and indeed, it seems that AMPK activations directly inhibits liver x receptor (LXR). The receptor is a protein and sometimes referred to as LXP.

These results indicate that AMPK directly inhibits ligand-induced LXR activity in addition to blocking production of endogenous LXR ligands.
source: “Mechanism of AMPK suppression of LXR-dependent Srebp-1c transcription” https://pubmed.ncbi.nlm.nih.gov/21647332/

This indicates that lean ketogenic individuals have remarkably elevated AMPK levels. It shouldn’t be a surprise really. This has already been studied very well. An example here shows that AMPK levels double in the liver when the animals are put on a ketogenic diet. 2-fold higher in the liver and 2 to 3-fold higher in muscle.

“A high-fat, ketogenic diet induces a unique metabolic state in mice” https://journals.physiology.org/doi/full/10.1152/ajpendo.00717.2006

Pharma Failure?

It is tempting that given all of the above you can simply develop a drug to inhibit CETP. So they did and had to stop the trial early because it caused more deaths. I couldn’t find much input about due to what the patients died from but there was a follow-up study that indicates it was not caused by the inhibition of CETP but due to side-toxicity.

The study said the following about the CETP inhibition:

Recent analysis suggests that failure may have been caused by off-target toxicity and that HDL is functional and promotes regression of atherosclerosis. New studies highlight the central importance of the ATP-binding cassette (ABC) transporters ABCA1 and ABCG1 in reducing macrophage foam cell formation, inflammation, and atherosclerosis. A variety of approaches to increasing HDL may eventually be successful in treating atherosclerosis.
source: “HDL, ABC transporters, and cholesterol efflux: implications for the treatment of atherosclerosis” https://pubmed.ncbi.nlm.nih.gov/18460328/

Finally

It seems clear to me that you need to get into a state where your body lowers CETP activity naturally and thereby increases your HDL-C. In my previous article on pathological high LDL we clearly see that a low HDL-C is a risk indicator along with obesity etc.

My advice: get onto the ketogenic diet, get lean and smile when you see your HDL-C rising because you know it is working.

I wish you Good Luck and enjoy the rest of your day!

—- T H E – E N D —-

Pathologic LDL cholesterol

Throughout all my investigations on the ins and outs of cholesterol, energy metabolism, diseases such as T2 diabetes, cancer, Alzheimer’s, ageing etc.. I learned a lot about the environment of which the circulating lipids can be seen as a proxy for it.

In the low carb community, as people get leaner there is a tendency for their LDL cholesterol (LDL-C) to rise over time. Naturally there is a concern because we are all very familiar with the message of increased risk for heart disease, atherosclerosis specifically.

What I want to do with this article is convince you of the possibility that not all high levels of LDL-C are equally bad.

Let’s assume for a minute that it does exist, a situation in which high LDL-C is healthy, except that situation is rarely seen. You have 10 of these people. Now you mix them in with a group of 990 people who have high LDL-C but these 990 people have a situation in which their high LDL-C is a proxy for high risk of atherosclerosis. Now you run a study on them, not knowing about these 2 different situations. You will compare this group against another group of 1000 people with low LDL-C and you follow them up for a very long and see which group has the most heart attacks. The group with high LDL-C has more heart attacks so naturally your conclusion is that high LDL-C is indicative of a higher risk. On average that is indeed true. The problem is that this is averaged out.

Those 10 people are swamped by the 990 and will not be noticed. This will lead research to think that all high LDL-C is bad.

What I will do now is first of all assume that there is such a split where high LDL-C is a proxy for ill health and where it is not a problem. I will call one group pathological LDL-C (patLDL) and the other group physiological LDL-C (phyLDL). This is analogous to pathological insulin resistance and physiological insulin resistance.

Quite a number of people have looked into this so I’m leaning heavily on their insights and will be mixing in my own. I hope to contribute in this topic of “high LDL-C always being bad” by making a side by side comparison.

For the record: this is analysis done for myself. I am just sharing this information with you and it is completely up to yourself to first of all validate what I’m saying is correct and it is your own responsibility for the actions you will take or not. In no way am I advising what you should do.

That said, lets look at patLDL first and then see if we can come up with research that shows there is indeed a phyLDL profile and check if the risk factors of patLDL are also present under phyLDL. If they are present, then it would be fair to conclude phyLDL is not really a thing isn’t it?

patLDL

First of all what are the official risk factors according to the NHS from the UK? I’ve highlighted the ones which are lifestyle dependent, where you can take action to change them.

increasing age
smoking
an unhealthy, high-fat diet
lack of exercise
being overweight or obese
regularly drinking excessive amounts of alcohol
other conditions, including high blood pressure, high cholesterol and diabetes
a family history of atherosclerosis and CVD
being of south Asian, African or African-Caribbean descent

https://www.nhs.uk/conditions/atherosclerosis/

In the US, their NIH department of National Heart, Blood and Lung institute is a bit more elaborate. I’ve highlighted a number of interesting focus points for later on.

Major Risk Factors

Unhealthy blood cholesterol levels. This includes high LDL cholesterol and low HDL cholesterol.
High blood pressure. At or above 140/90 mmHg over time. If you have diabetes or chronic kidney disease, high blood pressure is defined as 130/80 mmHg or higher.
Smoking. Smoking can damage and tighten blood vessels, raise cholesterol levels, and raise blood pressure. Smoking also doesn’t allow enough oxygen to reach the body’s tissues.
Insulin resistance. Insulin resistance may lead to diabetes.
Diabetes. The body’s blood sugar level is too high because the body doesn’t make enough insulin or doesn’t use its insulin properly.
Overweight or obesity.
Lack of physical activity. A lack of physical activity can worsen other risk factors for atherosclerosis, such as unhealthy blood cholesterol levels, high blood pressure, diabetes, and overweight and obesity.
Unhealthy diet. Foods that are high in saturated and trans fats, cholesterol, sodium (salt), and sugar can worsen other atherosclerosis risk factors.
Older age.
Family history of early heart disease.

“Studies show that an increasing number of children and youth are at risk for atherosclerosis. This is due to a number of causes, including rising childhood obesity rates.“

Emerging Risk Factors

High levels of a protein called C-reactive protein (CRP) in the blood may raise the risk for atherosclerosis and heart attack. High levels of CRP are a sign of inflammation in the body.
Inflammation is the body’s response to injury or infection. Damage to the arteries’ inner walls seems to trigger inflammation and help plaque grow.
People who have low CRP levels may develop atherosclerosis at a slower rate than people who have high CRP levels. Research is under way to find out whether reducing inflammation and lowering CRP levels also can reduce the risk for atherosclerosis.
High levels of triglycerides (tri-GLIH-seh-rides) in the blood also may raise the risk for atherosclerosis, especially in women. Triglycerides are a type of fat.
Studies are under way to find out whether genetics may play a role in atherosclerosis risk.

Other Factors

Sleep apnea. Sleep apnea is a disorder that causes one or more pauses in breathing or shallow breaths while you sleep. Untreated sleep apnea can raise your risk for high blood pressure, diabetes, and even a heart attack or stroke.
Stress. Research shows that the most commonly reported “trigger” for a heart attack is an emotionally upsetting event, especially one involving anger.
Alcohol. Heavy drinking can damage the heart muscle and worsen other risk factors for atherosclerosis.

https://www.nhlbi.nih.gov/health-topics/atherosclerosis

These are all well established risk factors. If the list is a bit overwhelming and hard to grasp at once, let me break down these factors in the light of the lipid profile that shows increased risk.

Lipid profile:

High LDL-C
Low HDL-C
High Triglycerides

Along with:

High blood pressure
Overweight/obesity
T2 diabetes
Raised inflammation
High levels of CRP
Insulin resistance
Smoking
Chronic Kidney Disease

Apart from smoking, all the other risk markers are all linked to insulin resistance.

High blood pressure: https://pubmed.ncbi.nlm.nih.gov/7512468/
Obesity: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC380258/
T2 diabetes: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3314346/
Inflammation: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2246086/
High CRP (which is an inflammatin marker: https://bmjopensem.bmj.com/content/3/1/e000236
Chronic Kidney Disease: https://pubmed.ncbi.nlm.nih.gov/27707707/

Is it feasible that the lipid profile reflects insulin resistance?

The 3 major components of the dyslipidemia of insulin resistance are increased triglyceride levels, decreased high-density lipoprotein (HDL) cholesterol, and changes in the composition of low-density lipoprotein (LDL) cholesterol.
source: “Insulin resistance and lipid metabolism” https://pubmed.ncbi.nlm.nih.gov/10418856/

The LDL-C/HDL-C ratio in men and LDL-C/HDL-C, TG/HDL-C, and non-HDL-C/HDL-C ratios in women might be clinically significant predictors of IR in healthy Korean adults.
source: “What is the most appropriate lipid profile ratio predictor for insulin resistance in each sex? A cross-sectional study in Korean populations (The Fifth Korea National Health and Nutrition Examination Survey)” https://dmsjournal.biomedcentral.com/articles/10.1186/s13098-015-0051-2

What you see in these ratios is that the risk goes up as LDL or triglycerides goes up and the risk goes down as HDL-C goes up.

Insulin resistance, as manifested by a high triglyceride/HDL-c ratio, was associated with adverse cardiovascular outcomes more than other lipid metrics, including LDL-c, which had little concordance.
source: “Study of the Use of Lipid Panels as a Marker of Insulin Resistance to Determine Cardiovascular Risk” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4625988/

We see here the same ratio back and they even found no use in looking at LDL-C.

It seems to support the case to state that the lipid profile is pathological if your LDL-C goes up, HDL-C goes down and triglycerides go up. Perhaps even more important is that your lipids are evolving into this scenario over time so that you see which way you are going.

If you keep all conditions the same, smoking or not and your activity level then only food is left to have a serious impact on your lipid profile.

phyLDL

You may or may not know this but food can have a very dramatic impact on your lipids.

Having read the previous section where you saw almost all risk factors, including the lipid profile, linked to insulin resistance…

Would you consider to be at risk for CVD under the following conditions?:

Lean (instead of obese)
Active (instead of sedentary)
Insulin sensitive (instead of insulin resistant)
Low hsCRP (instead of high hsCRP)
Low blood pressure (instead of high blood pressure)
No chronic kidney disease (instead of having it)
Not smoking (instead of smoking)
High HDL-C (instead of low HDL-C)
Low triglycerides (instead of high triglycerides)
Yet high LDL-C

So out of all the risk factors, only your LDL-C matches while we have seen that the ratios are better predictors, not the isolated LDL-C value. And the LDL-C value was seen in the light of insulin resistance.

Would you truly believe you are at risk?

Such a profile does exist among humans but is rarely seen. Rarely because it takes a specific diet and lean humans. Could they be the 10 people in our group of 1000 where 990 really are at an increased risk?

But before we look at the diet, lets have a look at endurance athletes who we can view as an example of fit and healthy individuals. I want to see what is happening to their lipid profile and then see how the lipid profile of the diet matches with it.

Endurance Athletes

Let’s just list up a few studies and see what they have to say about the lipid profile.

Low LDL-C/HDL-C and low triglycerides

“Long distance runners and body-builders exhibit elevated plasma levels of lipoprotein(a)” https://pubmed.ncbi.nlm.nih.gov/8187216/

2. Higher HDL-C and lower TC/HDL-C (TC = total cholesterol)

“Elevated high-density lipoprotein cholesterol levels in older endurance athletes” https://pubmed.ncbi.nlm.nih.gov/6465022/

3. Higher HDL-C and lower triglycerides

“High density lipoprotein metabolism in endurance athletes and sedentary men” https://pubmed.ncbi.nlm.nih.gov/2060090/

4. Higher HDL-C and lower triglycerides. This study looked at the clearance rate of triglycerides and found a strong negative relation with fasting triglycerides and a strong positive relation with HDL-C levels. So the lower your triglycerides and the higher your HDL-C, the faster you are able to clear triglycerides from the circulation.

“Elevated high-density lipoprotein cholesterol in endurance athletes is related to enhanced plasma triglyceride clearance” https://pubmed.ncbi.nlm.nih.gov/3374323/

5. Increase in HDL-C and lower triglycerides, if triglycerides started out high.

“The influence of exercise on the concentrations of triglyceride and cholesterol in human plasma” https://pubmed.ncbi.nlm.nih.gov/6376133/

I think you get the picture by now. They all report increase in HDL-C and a reduction in triglycerides. Yet none of them report on LDL-C except for the last one saying there is hardly any change.

If LDL-C would be so important for health, then why don’t we see it noticeably reduced in endurance athletes?

We have a bit of a baseline now so let’s look at how diet could be matching with the changes that we see in endurance athletes.

Diet

People who go on a ketogenic diet which is high in dietary fat intake and very low in carbohydrate intake (to stimulate easier ketone production) often tend to do it for weight loss. As they get leaner they may experience a rise in LDL-C. The most lean subjects, who may have gotten onto the diet while they were already lean, see their levels go sky high. Often they hear from their doctor that they have never seen this before.

I collected a sample from such people’s self-reported figures to see the correlation with ApoE version but that is not important. The graph shows you averages of in total 52 people. You can ignore the 2/3 and 4/4 groups because they have only 4 and 3 samples.

They have low triglycerides and very high HDL-C levels. The athletes usually have HDL-C levels of around 60 mg/dL from what I’ve seen in the papers.

Most of the people behind these numbers report an active lifestyle although that is not the case for all of them but they all have low body fat in common with athletes. They are generally health conscious and generally fit the phyLDL conditions.

Diet and Endurance

Just a trivia, how about mixing the diet in with endurance athletes? This study has been done and here are the results.

You see here that the HDL-C has gone up significantly higher. This has positively affected the triglyceride/HDL-C ratio. Triglycerides were already low in both groups. Also here we see a higher LDL-C in the low carb group.

“Paradox of hypercholesterolaemia in highly trained, keto-adapted athletes” https://pubmed.ncbi.nlm.nih.gov/30305928/

patLDL versus phyLDL

But back to the diet itself. Let’s review that list again. How does it compare to the pathological risk factors?

Reduction in inflammation: https://pubmed.ncbi.nlm.nih.gov/18046594/
Reverses T2D: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6104272/
Improves Chronic Kidney Disease: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7071259/ (perhaps confounded by weight loss) https://pubmed.ncbi.nlm.nih.gov/23611549/
Lowers blood pressure: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6695889/
Reduction in hsCRP: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5928595/

Lipid profile:

Very high LDL-C
Very high HDL-C
Low triglycerides

Taking everything into account, this profile is far from resembling that of the patLDL.

Finally

As you can see in this article, the profile of the lipids and risk factors associated with CVD do not fit with athletes nor with lean people on a ketogenic diet, nor with athletes on a ketogenic diet.

This comparison shows us that there is clearly a difference. There is indeed a case to create when elevated LDL-C is a bad sign but it should be seen in light with all the other factors. For the majority of people who are not on a ketogenic diet (the 990 people) you need to be worried. But for the small group of others who are on a ketogenic diet and fit the physiological high LDL-C, I’m not worried about CVD risk.

All the risk factors are not present and the lipid profile is different. LDL-C should not be looked at in isolation.

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The key to enhance performance on a high-fat diet

There is a professor (Louise Burke) who looked at athlete performance extensively in elite race-walkers. Shamefully the high-fat community has criticized her and attacked her because the results that she came up with showed that when it comes to world class athletes, there is no performance benefit and more likely there is a slight decrease.

That critique has been met with more research and the results remained the same.

Rather than criticizing and recognizing the facts for the given circumstances, I started to wonder why there could be an issue with performance. We’ve seen great benefits from fat adapted athletes meaning improved performance and markers but not at the high intensity that needs to be sustained during a race.

Why?

We know that under high intensity the contribution of fat to energy diminishes. It is not a great amount but still, it reduces.

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Object name is tjp0536-0295-f4.jpg — source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2278845/

The figure above comes from people who were not fat adapted. They have their peak fat oxidation at around 55% of VO2Max. When we look at a study from Jeff Volek then we see that maximum fat oxidation can shifts towards a higher intensity. The high carb group shows the same results as before, max fat oxidation at 55% while the LC group (very low carb) reached the peak at 70%.

source: https://pubmed.ncbi.nlm.nih.gov/26892521/

That is an impressive result so why doesn’t it result in improved performance at the highest intensities?

Carnitine

Without going into too much details, carnitine is needed to bring the long chain fatty acids (LCFA) into the mitochondria so that the fat can be used to produce ATP.

The following presentation helps greatly to understand why carnitine availability is an issue.

In short, at higher intensities there is not enough available carnitine to support the import of LCFA so that there is even a negative effect on its ability to import those fats.

That is a major blocking point if you are primarily fueled by fat.

In high carb athletes we see a strong reduction after 65% of VO2Max intensities. My guess is that we’ll see a similar effect at around 70~75% for the fat-adapted athletes.

source: https://www.youtube.com/watch?v=M-9hS_dPdrI

This is supported by another study looking at free carnitine. Subjects started at an average of 15.9 mmol per kg of dry weight. Exercise at 70% and 100% VO2Max resulted in a drop to 5.9 and 4.6. Less than a 3rd remains.

“Muscle carnitine metabolism during incremental dynamic exercise in humans” https://pubmed.ncbi.nlm.nih.gov/2327259/

Increase carnitine content

So naturally people will have the reflex of supplementing carnitine and indeed, when they succeed we see a number of changes. It translates into a greater reduction in lactate which shows that more fat is used for energy production.

When testing the results of a 20% increase in carnitine content in a time trial effort of 30 minutes at 80% VO2Max we see that all participants improved and on average had an 11% increase in performance. The study subjects were recreational athletes so the results may not equal in a similar performance gain for top-level athletes but it shows promise and 11% is a very big deal if this could be achieved in such athletes.

“Chronic oral ingestion of L-carnitine and carbohydrate increases muscle carnitine content and alters muscle fuel metabolism during exercise in humans” https://pubmed.ncbi.nlm.nih.gov/21224234/

How?

Naturally if it offers a performance enhancement we’re interested. It turns out that it is not as simple as taking a carnitine supplement. Bacteria in the gut seem to love it and not even intravenous supplementation made any change.

What researchers did find out is that it requires insulin and works via a sodium transporter. So they recommend to take carbohydrates along with the supplement.

But research comes with varying results. For example 3 months of supplementation shows no increase while 6 months do.

Three months of dietary supplementation with a combination of carnitine and CHO had no effect, but after 6 months muscle carnitine content increased by 21%. The necessity of using a very long supplementation period demonstrates the difficulties involved and explains the failure of previous studies with shorter intervention periods.
source: “Boosting fat burning with carnitine: an old friend comes out from the shadow” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3099008/

If you however want to stay on a ketogenic diet and be as fat adapted as possible, I think there are alternative ways to increment muscle carnitine levels.

I know we are not chicken but when looking at what they did, they were able to increase the body mass while reducing the fat content. How they achieved this was by varying protein content in the diet and supplementing with carnitine. It looks like the combination is a great way to increase the absorption and usage.

“Effects of dietary L-carnitine supplementation and protein level on performance and degree of meatness and fatness of broilers” https://pubmed.ncbi.nlm.nih.gov/9404545/

From the youtube presentation it was clear that insulin is required. They experimented on one hand with 80gr carbs and later on also had experiments with 40gr carbs mixed with protein and had similar results.

Purely a guess but I think that the insulin response to a meal is already sufficient for the absorption so low carb athletes could make sure that they take a supplement during meals.

But also here the results are conflicting. The inclusion of carbs and protein seem to blunt the uptake in an acute phase. Conflicting because from the youtube presentation there was successful results using a mix of 40gr carbs and 13gr protein in 24 weeks.

“Protein ingestion acutely inhibits insulin-stimulated muscle carnitine uptake in healthy young men” https://pubmed.ncbi.nlm.nih.gov/26675771/

The following study, although a very specific case seems to hint at a redistribution mechanism. This may indicate why it could take some time before muscle carnitine increases. It is possible that there is a lot of tissue in the body that takes up carnitine so regular and prolonged higher intake of carnitine may be necessary to create a saturation effect before muscle carnitine increases.

“Muscle and plasma carnitine levels and urinary carnitine excretion in multiply injured patients on total parenteral nutrition” https://pubmed.ncbi.nlm.nih.gov/16829425/

There is also a trend towards carnivore eating, it would be interesting to compare carnitine levels in these people/athletes to see if natural sources are sufficient to increase levels.

So clearly more research is required and hopefully we can see another step up in athlete performance.

What are the best tolerable ways to increase carnitine in the shortest period of time?
How high can carnitine levels be pushed in athletes?
Does increased carnitine provide a performance benefit for high-fat athletes and does that benefit still hold if we also increase carnitine levels in high-carb athletes?
Do we have any non-invasive proxies so that we can avoid muscle biopsies to check carnitine levels?
Where lays the true limit of oxygen availability?

A final word on the fat part

One other way to overcome the limitations that carnitine levels impose is to enhance the availability of short and medium chain fatty acids in the body. However, levels must be sustained for the whole duration of the race. It is likely that the absorption of these fatty acids into the mitochondria goes faster and will be depleted or reduced quicker. Fueling with fats during the race is not that straightforward.

A study looking at fat oxidation noted a quite clear difference. This was achieved through infusion so not a practical approach during racing but it shows the potential.

Furthermore, the percentage of oleate uptake oxidized decreased from 67.7 +/- 2.8% (40% VO2peak) to 51.8 +/- 4.6% (80% VO2peak, P < 0.05), whereas the percentage of octanoate oxidized was similar during exercise at 40 and 80% VO2peak (84.8 +/- 2.7 vs. 89.3 +/- 2.7%, respectively)

“Regulation of plasma fatty acid oxidation during low- and high-intensity exercise” https://pubmed.ncbi.nlm.nih.gov/9227453/

When looking at high performance and circulating fat we see that there is also a reduction in circulating fatty acids which also support the idea that in case of highest performance you need to fuel fatty acids.

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“The Effects of a Ketogenic Diet on Exercise Metabolism and Physical Performance in Off-Road Cyclists” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4113752/

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