It appears to be common knowledge that eating eggs will raise your cholesterol level. Eggs are a rich source of cholesterol, so it stands to reason that eating them would raise total cholesterol levels in the body. However, things that seem self evident may actually not be the way they appear to be at first sight.
It turns out that most of the cholesterol in our blood comes from our own liver. The body has the ability to adjust its manufacture rate of cholesterol so that when we eat more of it, less is made, keeping the total levels about the same. Why would we make our own cholesterol? It is a precursor for many important molecules in the body, such as the sex hormones estrogen and testosterone, and the corticosteroids cortisone and aldosterone. Cholesterol is also incorporated into cellular membranes where it helps maintain the optimum degree of fluidity.
The physician and researcher Uffe Ravnskov (1) challenged the conventional wisdom that the cholesterol in eggs raises the cholesterol levels in the blood with an experiment he performed on himself. He measured his total cholesterol levels while increasing the number of eggs he ate each day, until he reached eight eggs a day. He found that his cholesterol levels did not increase, but remained at the same level as when he ate his customary two eggs a day. Dr. Ravnskov's experiment only lasted eight days, during five of which he was eating eight eggs a day.
A similar result was obtained in a controlled Canadian study (2) testing 28 male individuals with normal cholesterol levels over a period of 14 weeks (including times at which the subjects were not eating eggs). The total cholesterol levels of the individuals in the study did not change significantly while eating 4 eggs a day. They actually did go up by 6.6% average, but this amount was not statistically significant in that study. The HDL cholesterol levels increased by the also non-significant amount of 3.8%, consuming a total average of 715 mg cholesterol in the four eggs a day (about 2.4 times the maximum recommended daily amount of 300 mg in the US). The same study did find a significant increase in the platelet membrane levels of the essential fatty acid DHA in the subjects who were eating eggs laid by hens eating a diet enriched in flaxseed.
None of the study subjects in the previous study developed significantly raised cholesterol levels. However, 2 out of 25 already hypercholesterolemic participants in a different study (3) developed a significant increase in their total and LDL cholesterol levels after eating 12 eggs a week for 6 weeks.
As for many questions in life, there is no absolute answer. For most people, their cholesterol levels will not increase from eating an egg a day. This may not be true for a subset of the population, especially among those who already have high cholesterol levels. The subjects in the last study mentioned were on a low-fat diet, which may have had an important impact on the results, as low-fat can usually be equated with high-carbohydrate. According to Dr. Ravnskov, high cholesterol levels are not correlated with any reduction in life expectancy or increase in heart disease, especially for those over the age of 47 years, making the whole fixation on cholesterol a moot point.
Long accepted tenets of nutrition involving fats, cholesterol and carbohydrates are being revisited and challenged with increasing regularity. This is a time for going beyond the sound-bytes and looking closer to the experimental sources of the data for answers that will stand up to scrutiny.
References:
1. Ravnskov, U. Fats and Cholesterol are Good For You! GB Publishing, Sweden. 2009
2. Ferrier, L.K., L.J. Caston, S. Leeson, J. Squires, B.J. Weaver and B.J. Holub. Alpha-linolenic acid- and docosahexaenoic acid-enriched eggs from hens fed flaxseed: influence on blood lipids and platelet phospholipid fatty acids in humans. The American Journal of Clinical Nutrition 62: 81-86. 1995
3. Lewis, N.M., S. Seburg and N.L. Flanagan. Enriched eggs as a source of n-3 polyunsaturated fatty acids for humans. Poultry Science 79: 971-974. 200
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