Saturday, August 31, 2013

Even If You Ate A Cholesterol-Free Diet, Your Body Would Make All It Needs

Interesting discussion over on Jack Norris' site about a woman who gave up her vegan diet and began eating animal foods because she didn't feel well:

The Winter of Their Discontent

Norris, a registered dietitian, hypothesized that the woman's "low" cholesterol was the cause of her feeling unwell. He said, "She was craving eggs because her body needed cholesterol." Cholesterol is only found in animal foods.

I thought that was an unusual pronouncement from a dietitian, a vegan advocate no less, because the human body, as anyone schooled in nutrition would know, makes its own cholesterol. Cholesterol is not an essential nutrient:
"Even if you ate a completely cholesterol-free diet, your body would make the approximately 1,000 mg it needs to function properly."
- Harvard Health Publications: CHAPTER 1: Understanding Cholesterol
In fact, the raw material for the production of cholesterol (and triglycerides) is a small 2-carbon molecule called acetyl-CoA, which comes from the breakdown of carbohydrate (and fat and protein), a nutrient that vegan diets provide in great amounts.

The pathway for cholesterol production is complex. It requires many different enzymes and utilizes many feedback loops. (Statins lower cholesterol by impeding the action of one of those enzymes, HMG-CoA synthase.) This elegant complexity and redundancy and recycling is at the heart of homeostasis.

If it is true that the woman's cholesterol level was the cause of her feeling unwell (that was not established), given that most of our cholesterol comes from in-house production, this points to some disturbance or malfunctioning of the cholesterol synthesis pathway. It does not point to her not eating enough cholesterol.

By the way, I saw that the woman was eating not only a vegan diet but a raw food diet. It is difficult to thrive on a diet of raw plant food. Richard Wrangham (who argues in his book "Catching Fire" that "without cooking, the human brain (which consumes 20-25% of the body's energy) could not keep running.") said that people who eat mostly raw food "thrive only in rich modern environments," and they usually feel very, very hungry."

Even if you did live in a cooperative environment and could access adequate amounts of raw plant food, you'd have to consume a lot of calories. (Wrangham: Because raw food is harder to digest, it takes more calories to get the calories out of it, and you get fewer calories from it anyway.) You also have to spend many hours a day just chewing.


Philippa said...

It makes little sense to me either that the woman's body was craving cholesterol, though it is logical to me that she needed something else she wasn't getting enough of in her vegan diet.

Neal Barnard talks about cutting out animal fats, at least in part because of dietary cholesterol. This is something else that puzzles me, because, as you point out, it is well-known that the human body produces its own cholesterol.

Healthy Longevity said...

Jack Norris gets a bit too excited whenever some apparent vegan claims they feel unwell because of a low cholesterol level.

Brown and Goldstein stated:
In view of the 10 to 1 gradient between concentrations of LDL in plasma and interstitial fluid, a level of LDL-cholesterol in plasma of 25 mg/dl would be sufficient to nourish body cells with cholesterol. This is roughly one-fifth of the level usually seen in Western societies. Several lines of evidence suggest that plasma levels of LDL-cholesterol in the range of 25-60 mg/dl (total plasma cholesterol of 110 to 150 mg/dl) might indeed be physiologic for human beings. First, in other mammalian species that do not develop atherosclerosis, the plasma LDL-cholesterol level is generally less than 80 mg/dl. In these animals the affinity of the LDL receptor for their own LDL is roughly the same as the affinity of the human LDL receptor for human LDL, implying that these species are designed by evolution to have similar plasma LDL levels. Second, the LDL level in newborn humans is approximately 30 mg/dl, well within the range that seems to be appropriate for receptor binding. Third, when humans are raised on a low fat diet, the plasma LDL-cholesterol tends to stay in the range of 50 to 80 mg/dl. It only reaches levels above 100 mg/dl in individuals who consume a diet rich in saturated animal fats and cholesterol that is customarily ingested in Western societies.

Bix said...

Philippa, cholesterol we eat is handled differently than cholesterol we make. That which we eat must travel through the bloodstream after being absorbed. Some of it goes to the liver where it's repackaged and travels through the bloodstream again. Cholesterol we make in a cell is often used locally and doesn't have to travel, and so doesn't increase the risk for plaque build-up. Nearly all tissues can make their own cholesterol.

Philippa said...

Bix, if I'm understanding you correctly, you're saying that it is ingested (and not manufactured) cholesterol that leads to arterial plaque build-up.

If that is so, why is it that both vegetarians and meat-eaters are able to contract CVD?

Bix said...

I said ... Cholesterol we eat is transported differently than cholesterol we synthesize. This difference impacts risk. Cholesterol by itself doesn't cause atherosclerosis. Atherosclerosis is multifactorial, it has many interacting variables.

I don't think you contract cardiovascular disease, like you contract a virus. I think you develop it, from what you eat and your lifestyle. Vegetarians have been shown to have less heart disease than meat-eaters.

Here's a recent study:

In 44,561 men and women in EPIC-Oxford cohort study, March 2013:

"Vegetarians had a 32% lower risk (HR: 0.68; 95% CI: 0.58, 0.81) of IHD [ischemic heart disease] than did nonvegetarians."

"Consuming a vegetarian diet was associated with lower IHD risk, a finding that is probably mediated by differences in non-HDL cholesterol, and systolic blood pressure."


Vegetarian Diets in Cardiovascular Prevention, August 2013

"There is growing evidence that consumption of a vegetarian diet as well as specific components of a vegetarian diet lower the incidence of cardiovascular disease (CVD) and death. Vegetarian diets lower the probability of developing CVD, are effective in altering serum lipids, are beneficial in reducing blood pressure, improve glycemic control and insulin sensitivity, reduce weight, and lower mortality. Vascular effects of a vegetarian diet include a thinner carotid IMT and lower brachial artery resistance."

Angela and Melinda said...

I've always heard your body manufactures what it needs. But thanks for clarifying the difference, Bix, b/tw made and ingested cholesterol!

RB said...

Could very low cholesterol of 95 mg/dl be an indication that the women wasn't getting enough fat in her diet? If she was eating a raw food vegan diet that could be a possibility. Diets of fruit and vegetable may not have enough fat. Fat is needed for the body to absorb fat soluble vitamins, make tissues and manufacture hormones. Another thing could be a protein deficiency. Again, just fruit and vegetable may not be enough. Beans, seeds, grains, nuts and legume need to be part of a vegan diet to ensure enough fat and proteins in the diet. It is hard to know the real issue from the few details in the Jack Norris post. A vegan diet is not necessarily a healthy diet if it is improperly designed (i.e. missing foods with needed nutrients).

Angela and Melinda said...

The two studies you posted in the comments dealt with "vegetarians"--as we, in this country, distinguish b/tw "vegetarian" and "vegan," I'm wondering if the studies discuss how they define "vegetarian".... I did click through on the links and didn't see anything. Do you know?

Bix said...

Yes, Angela and Melinda, here:

EPIC–Oxford: lifestyle characteristics and nutrient intakes

Bix said...

RB, I wouldn't say that 95 mg/dl, by itself, indicated disease. There are people who eat low-fat vegan diets who have total cholesterol ~100 mg/dl.

My belief is that she was experiencing a placebo effect. That doesn't negate a deficiency, many possible ones you mentioned. But...

If someone feels unwell, and they eat something, and "within hours" they feel better, or at least different. ... was it the thing they ate? Could be. Drugs and alcohol have this effect. But if the food supplied a nutrient the person was deficient in, it would take longer than an hour to have an effect.

e.g. If, say, you were deficient in iron and you ate some iron, you would have to absorb it, transport it, manufacture new hemoglobin with it, manufacture new red blood cells that contained the new hemoglobin, load it with oxygen, send it to deplete tissues, offload the oxygen, transport it into mitochondria, set it up to receive electrons coming at it from the electron transport chain, so that ATP, which is a form of stored energy in the body, can be produced. And you would have to make more than just a few molecules of ATP to "feel" it. This would take more than an hour.

Angela and Melinda said...

Thanks Bix, re my question of vegetarian vs vegan in the study, but unfortunately the link is unavailable to me. :-(

Bix said...

Hm, try this, and click PDF:

Angela and Melinda said...

Thanks Bix!

Anonymous said...

We ingest (i.e., take in) cholesterol in many of the foods we eat and our body produces (“synthesizes”) cholesterol de novo from various precursors. About 25% of our daily “intake” of cholesterol – roughly 300 to 500 mg — comes from what we eat (called exogenous cholesterol), and the remaining 75% of our “intake” of cholesterol — roughly 800 to 1,200 mg – is made by our body (called endogenous production). To put these amounts in context, consider that total body stores of cholesterol are about 30 to 40 gm (i.e., 30,000 to 40,000 mg) and most of this resides within our cell membranes. Every cell in the body can produce cholesterol and thus very few cells actually require a delivery of cholesterol. Cholesterol is required by all cell membranes and to produce steroid hormones and bile acids.