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Harvard School of Public Health debunks egg study

Harvard School of Public Health (HSPH) has commented on the study by Zhong and colleagues, published in the March 15th issue of JAMA, that examined the impact of eggs in the diet.

The study attempted to answer the question whether eggs or cholesterol from foods are associated with an increased risk of cardiovascular disease (CVD) or deaths from any cause. The study was a pooled analysis of data from six prospective studies that had followed 29,615 U.S. men and women for up to 31 years.

HSPH summarises the findings as follows:

+ For every additional 300 mg of dietary cholesterol eaten per day, the risk of CVD and all-cause mortality was higher by 17% and 18%, respectively. These associations became nonsignificant after adjustment for consumption of eggs and red meat. In the U.S. population, eggs and meats contribute 25% and 42% of total dietary cholesterol, respectively.

+ For each additional half of an egg consumed daily, the risk of CVD and all-cause mortality was higher by 6% and 8%, respectively. When the authors looked more closely, dietary cholesterol intake was more strongly associated with risk of stroke than heart disease, and it was associated with both CVD and non-CVD deaths.

This study, notes HSPH, includes a relatively large sample and a long duration of follow-up. However, it continues, a major limitation is the use of a single measure of diet to look at outcomes up to 30 years later. During this time, some individuals may have changed their diet after developing high cholesterol or other conditions, which may influence the results of the study. These findings, HSPH believes, should be interpreted in the context of several previous studies, which have shown that low to moderate egg intake is not associated with a higher risk of CVD in generally healthy people.

“These new findings may rekindle the debate about the role of dietary cholesterol and egg consumption in cardiovascular disease, but would not change general healthy eating guidelines that emphasize increasing consumption of fruits, vegetables, whole grains, nuts, and legumes and lowering consumption of red and processed meats and sugar,” said Dr. Frank Hu, Chair of the Department of Nutrition at the Harvard Chan School of Public Health, who was not involved in the study.

“For those who are generally healthy, low to moderate intake of eggs can be included as part of a healthy eating pattern, but they are not essential. For example, there is a range of other foods one can choose for a variety of healthful breakfasts, such as whole grain toast with nut butter, fresh fruits, and plain yogurt.”