When talking to friends (and worse, acquaintances) about the paleo diet, often the first sticking point is my suggestion that eating meat and eggs is healthy. The message that cholesterol is dangerous is common in the public consciousness, specifically the idea that eating cholesterol-heavy foods leads to heart disease. In this post, I review the connection between dietary cholesterol (ie how much is in the foods you eat) and serum cholesterol, and the relationship to heart disease.

“it is still important to limit the amount of cholesterol you eat” – Harvard School of Public Health

“a diet high in cholesterol can contribute to elevated blood cholesterol levels” – Mayo Clinic

“The jury is still out on whether there is a direct link between dietary cholesterol, which is found in the foods we eat, and blood cholesterol, which is manufactured by the body” – about.com

Association

Early studies found that high blood cholesterol levels are associated with heart disease. But association is not causation. Does high cholesterol cause heart disease? Does heart disease cause high cholesterol levels? Or are they both caused by some separate, third factor?

The message got out: high cholesterol levels are associated with heart disease. But the caveats, caution, and confusion did not. Many people relied on reporters to interpret the dense scientific jargon of research papers and distill it to something that you could rely on when shopping at the grocery. The media filled with the simple message to avoid eggs, red meat, and other cholesterol-rich food. My family switched from butter to margarine, as did many Americans in the middle of the 20th century.

Studies

In the scientific community, after the initial association was identified, scientists set off to find out what causes what. And that’s when the simple model broke down. Cholesterol turned into Good Cholesterol (HDL) and Bad Cholesterol (LDL), and then that broke down too. Now there’s light, fluffy LDL and small, dense LDL and … bah! Life was just easier when we could avoid eggs and everything would be OK.

Strangely, Ancel Keys (who kickstarted the whole hatefest on saturated fat) authored a study claiming no link between diet and serum cholesterol. The oft-cited Framingham study also produced such a study, although it was never published. A 1976 study in Michigan found no link between food (not just dietary cholesterol) and serum cholesterol. Ravnskov links to a whole bunch more studies.

One thing to note is that these studies found no correlation with the ranges of their study population. Maybe everyone in each group already ate so much cholesterol that more didn’t matter? Maybe the range of nutrients in the diet wasn’t enough to effect a change in cholesterol? Yet the cholesterol values did vary widely; something was causing spikes in cholesterol, but it wasn’t anything that the researchers measured. It could be genetics (such as hypercholesterolemia), an untracked element of the food, etc. One Finnish study found that reducing saturated fat and cholesterol intake led to higher serum cholesterol, and studies on indigenous hunter-gather populations such as the Masai indicated that ultra-high-fat-and-cholesterol diets themselves didn’t lead to CVD.

Homeostasis

The body is replete with homeostatic systems, that is, systems that try to maintain a constant level of some hormone or enzyme or other protein or chemical in your body. Cholesterol is one such homeostatic system. The liver produces cholesterol as part of a complex balancing system. Cholesterol is a precursor to dozens of hormones, including Vitamin D and the sex hormones testosterone and estrogen; it’s used to build cell walls; and insulates nerve fibers. It also plays a role in inflammation, such as repairing damaged tissue after trauma or disease. It’s a critical molecule, and your body will manufacture about 3000 mg of cholesterol each day — that’s the equivalent of over a dozen eggs.

Why would a bit of extra cholesterol in the diet lead to catastrophic disease? Our bodies are built to use cholesterol, not to expel it like a waste or toxin.

The Myth

Yet somehow the myth was born. Perhaps from a confusion between dietary cholesterol and serum cholesterol, maybe a mistake made by news reporters. The myth persists, if not in research than at least in the public consciousness.

Although carefully controlled, short-term trials have found that eating cholesterol raises serum cholesterol values, that raise is just a blip. No correlation has been found in long-term studies. Your body regulates cholesterol levels in response to disease and trauma in addition to the daily needs of living. The cholesterol in your diet won’t kill you.