I’ve already written about why I think the carnivore diet is unhealthy, but some, at least for a time, seem to thrive on it.
The carnivore diet has gotten a lot of ink, but the theory I outline below is a new one. It’s just a theory, but my belief is that many people who have success on the carnivore diet actually have a rare genetic condition, known as sitosterolemia, that prevents their body from excreting the plant sterols they eat.
Instead, these sterols pool and cause inflammation.
What are plant sterols and what is sitosterolemia?
Cholesterol is a form of fat found in animals, and sterols are fats found in plants. Our bodies make cholesterol, but plant sterols can only enter the body through diet. We have to eat them otherwise they won’t show up in the blood. Foods like oats, wheat, beans, nuts and seeds, vegetable oils, and avocado have the highest amounts of sterols, but all plant foods contain some. In other words, the only way to go on a sterol free diet would be to eat nothing but meat.
Sterols are usually touted as healthy because they compete with cholesterol for absorption and have shown an ability to lower heart health markers like LDL-C. In most people, sterols like beta-sitosterol are excreted, they don’t stay in the body. But in others, especially people with mutations in the ABCG8 genes, the sterols hang around and are absorbed into the blood stream. You can see levels of sterol on advanced blood tests like the ones offered by labs like Boston Heart Diagnostics as part of a “cholesterol balance score.” Because humans make 80% of the cholesterol in our bodies, measuring cholesterol won’t do us much good in understanding how much cholesterol we are absorbing, so scientists use plant sterols as a proxy. By measuring sterols, we get an idea of how cholesterol is circulating in the body and how much we absorb. If our sitosterol levels are high, we are an absorber of cholesterol and sterol, or so the thinking goes.
Side note: there is major controversy over hyper absorbers of sterol also hyper absorb cholesterol. In the case of the best carnivore dieters, they may only be absorbing the sterol and not the cholesterol, leaving them with a perfect constitution, in some ways at least, for a meat only diet.
The issue first came on my radar when I noticed high levels of beta-sitosterol in my blood after a recent draw.
I had been eating a diet very high in sterol, which put my levels at 3.9 mg/dl, the highest they’ve been. I know from previous blood draws that 1.8 mg/dl was my lowest, which means I am an absorber of cholesterol. But for people with sitosterolemia, 3.9 mg/dl of sitosterol is nothing. Some people with the condition have triple these amounts and often much more. They have tons and tons of plant sterols circulating in their blood.
The ABCG8 genes and sterol clearance
Variants in the ABCG8 genes are associated with sitosterolemia. In essence, the ABCG8 genes helps the body get rid of plant sterols and certain “mutations” in the gene cause sterol to hang around where they can do damage.
I know by analyzing my SNPs and labs that I don’t have sitosterolemia, but I do have two SNPs in my ABCG8 genes, which led me to theorize: what if just as urea cycle function fluctuates from person to person, which is part of the reason why certain people feel great on a high protein diet and others feel terrible, sterol clearance fluctuates as well?
Kids born with mutations in genes like CPS1, which govern the body’s ability to break down the ammonia generated by digesting animal protein, get very ill the minute they eat any protein. They just don’t have the enzymes in their body to deal with the ammonia and any levels immediately become toxic.
It’s possible this is also the case for sterol absorption. Some people clear 95% of what they eat, others clear 50%, and perhaps certain people only clear 25% or less. Diminished ABCG8 function causes a rapid build up of sterol, which results in an immediate inflammatory cascade that continues until the sterol is no longer ingested. What other explanation could there be for the most hard core carnivore dieters casting leafy greens in the role of dietary bad guy? Leafy greens contain sterol. For most of us they are healthy, but perhaps for a very small subset of the population, they do damage.
In other words, we all absorb sterol at different rates based on our unique genetic profile, and those with an autoimmune condition, especially that impacts joint health and mood, could be undiagnosed cases of sitosterolemia.
Carnivore dieters have sitosterolemia symptoms
Now, there are some arguments against this theory, one of which is that those with sitosterolemia tend to develop heart disease very early in life, sometimes as early as childhood, and the most famous carnivore dieters don’t seem to fall into this category. However, sitosterolemia is said to be under diagnosed (presumably because 99.99% of people never have their sterol levels measured) and if you take a look at Mikhaila Peterson’s blog (Mikhaila is perhaps the best known carnivore dieter) many of the symptoms she lists are consistent with a sterol absorption problem. She mentions “painful bumps” on her skin and debilitating joint pain that caused her to suffer through multiple joint replacements.
Could the “bumps” Mikhaila talks about be xanthomas, which are lipid deposits sitosterolemia patients often have?
Those who are over absorbing sterol also have major problems with joints as the result of sterol deposits actually accumulating in the joints.
To quote the NIH article on sitosterolemia:
Some people with sitosterolemia develop small yellowish growths called xanthomas beginning in childhood. Xanthomas consist of accumulated lipids and may be located anywhere on or just under the skin, typically on the heels, knees, elbows, and buttocks. They may also occur in the bands that connect muscles to bones (tendons), including tendons of the hand and the tendon that connects the heel of the foot to the calf muscles (the Achilles tendon). Large xanthomas can cause pain, difficulty with movement, and cosmetic problems.
The interesting thing about sitosterolemia is that patients who have it often have normal cholesterol levels.
In closing, I still think the carnivore diet is a bad idea for most people. Mikhaila Peterson is very brave to share her story, and you can’t help but admire her quest to find out what works for her body. Having said that, most people won’t have the extreme reaction to eating plants that the carnivore dieters have.
Testing for sterol absorption
If you want to have your sterol levels tested, Boston Heart Diagnostics is a great lab, but you’ll need to call them to ask which, if any, doctors in your area offer their tests.
Below, I have also included a list of the SNPs associated with sitosterolemia. If you have your 23andme or Ancestry file, these SNPs will be included.