Q: What is the evidence that dietary cholesterol or other fat influences serum cholesterol?
A: Foods high in cholesterol, like eggs or cheese, can raise blood cholesterol levels, though the effect is relatively modest and varies from person to person. The best evidence available suggests that saturated fat, rather than dietary cholesterol per se, is the major contributor to serum cholesterol.
In 1991, The New England Journal of Medicine described the case of an 88-year-old man who ate 25 eggs a day for at least 15 years and had normal cholesterol levels and apparently normal arteries. This report challenged a central dogma of medicine: namely, that dietary cholesterol leads to elevated serum cholesterol and atherosclerosis. That belief arose in 1913, when Russian scientist Nikolai Anichkov observed that rabbits developed atherosclerosis after being fed a high-cholesterol diet.
Over the years, the association between diet and atherosclerotic plaque grew, but controversy grew as well. Critics noted that rabbits do not consume cholesterol in the wild, and humans do not consume cholesterol in isolation. The vast majority of foods that are high in cholesterol, like steak or butter, are also high in saturated fats. Notable exceptions to this rule are egg yolks and shellfish, such as shrimp, lobster and crab.
In 1965, a landmark Harvard study — one which could not be replicated today because of evolving ethical standards, as it was performed on schizophrenic patients confined to a mental hospital — showed that saturated fat exerted a greater effect on serum cholesterol than dietary cholesterol did. Subsequent studies supported this conclusion, including the 20-year Western Electric Study of 1,900 men from 1981 and an analysis of 395 experiments that appeared in the British Medical Journal in 1997.
Ultimately, the weight of the evidence led to changes in recommendations. In 2013, the American Heart Association stated, “There is insufficient evidence to determine whether lowering dietary cholesterol reduces LDL-C,” or “bad” cholesterol.” More recently, the Dietary Guidelines Advisory Committee, whose recommendations inform U.S. Department of Agriculture policy, dropped its previous recommendation to limit dietary cholesterol, advising that “cholesterol is not a nutrient of concern for overconsumption.”
It should be emphasized that there is great individual variation in the response to dietary cholesterol. Some people are like the 88-year-old man described above and are able to maintain a normal serum cholesterol despite a high intake of dietary cholesterol. Others are more like Anichkov’s rabbits, and their serum cholesterol levels rise in response to high levels of dietary cholesterol.