Diabetes Risk is Reduced by Egg Consumption

A recent study out of Finland found that men who ate chicken eggs on a regular basis had a lower risk of developing type 2 diabetes mellitus. Like a number of other recent studies this article stands in contrast to what was once the conventional wisdom: that eating foods high in cholesterol would increase your risk of heart disease and its risk factors.

This study also reminds us of how one of the most important aspects of health care is appreciating the difference between using a pathophysiologic rationale to solve a clinical problem vs. the best available medical evidence.

Late in 2013, the British Medical Journal published a meta-analysis of 17 cohort studies. The included studies used a food frequency questionnaire to determine dietary intake and how it correlated with the development of coronary artery disease or stroke. This meta-analysis found that regular egg consumption did not increase the risk of heart disease or stroke with the exception of a slight increase in heart disease risk among diabetic patients, but a decreased risk of hemorrhagic stroke. This study was built on a number of smaller studies where the initial assumption (eating high cholesterol foods would likely increase the risk of heart disease) made reasonable physiologic sense. When studied using meta-analysis methods, the results found that eggs were actually not likely to increase the risk of heart disease or stroke.

This new study from Finland included over 2,000 men between ages 42 and 60. The study, called the Kuopio Ischemic Heart Disease Risk Factor Study (KIHD) and conducted in the late 1980s, provided almost 20 years of follow-up. It found eating 4 eggs per week resulted in a relative risk reduction of 37% for the onset of type 2 diabetes compared to men who only ate 1 egg per week. What is most startling about this study was this association persisted even after correcting for confounding factors such as physical activity, BMI, tobacco abuse, and consumptions of fruits and vegetables.

This study comes on the heels of a variety of observational studies on other exposures and diabetes risk. Recent headlines include results from a study on high-fat dairy products lowering the risk of type 2 diabetes. Another study found that yogurt consumption reduced the risk of type 2 diabetes. Fish-derived omega 3 fatty acid supplementation lowered risk of type 2 diabetes (also out of Finland and published in Diabetes Care 2014). And probably most importantly, eating more fruits and vegetables lowers the risk of type 2 diabetes (another food frequency questionnaire based study from the Nurses’ Health Study, Nurses’ Health Study 2, and the Health Professionals’ Follow-Up Study, and written by faculty at the Harvard School of Public Health and published in the British Medical Journal in 2013).

With so many things correlating with a lower risk of type 2 diabetes, how can this diagnosis be epidemic in the US and seemingly around the world? This is best answered by understanding that initial medical research looks for trends and correlations. They prove very little. Some are very meaningful, like the data on eating a diet high in fruits and vegetables which has repeatedly been found to lower diabetes and CHD risks. Others, like fish derived omega 3 supplementation, are less so, and lead patients and providers to recommend actions that are unlikely to improve outcomes. Remember the “no fat” craze of the 1990s? But this latest study from Finland has done a fantastic job of getting close to proof by controlling for so many variables. Eggs are unlikely to worsen your heart or diabetes risks.

Why is this clinically important? Most importantly, if patients do not have diabetes, tell them it is OK to eat at least 4 eggs per week without increasing risk of type 2 diabetes or premature heart disease. Also remind them this will provide very little protection if they are not otherwise maintaining a healthy lifestyle of aerobic activity, a diet high in fruits and vegetables, and refraining from tobacco use. This should also be a healthy reminder for both us and our patients that just because something makes logical sense, it may not be so in clinical practice.

Large studies like meta-analyses help us diminish bias and provide great opportunity to question some of the assumptions we make. Maintain a healthy skepticism about applying our assumptions to medical decision making, and enjoy an omelet now and again.