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Ask the doctor: What the evidence shows about eggs as part of a healthy diet

Q. Are eggs bad for your health, or not? I hear different things about them.

A. I was taught—first by my parents, and then in medical school—that you should eat eggs infrequently. The reason? Egg yolk contains lots of cholesterol, so eggs would raise your blood cholesterol levels and increase your risk of heart disease. Seemed reasonable, so I reserved eggs for Sunday mornings only.

Eggs did also contain some heart-healthy substances: protein, vitamins B12 and D, riboflavin, and folate. But the negative effects of cholesterol were thought to trump the positive effects of these substances.

Then research discovered something paradoxical: saturated fats in your diet raise your blood levels of total cholesterol and “bad” LDL cholesterol a lot more than does cholesterol in your diet. Why? Because most of the cholesterol in your body does not come from your diet. Rather, it is made by your liver. And saturated fats in the diet cause your liver to make lots of cholesterol.

Image: Thinkstock
Nutrition Facts
One large, fresh whole egg
calories: 72
protein: 6 grams
total fat: 4.7 grams
saturated fat: 1.5 grams
calcium: 28 mg
potassium: 69 mg
magnesium: 6 mg

The next discovery came from large observational studies—many conducted here at Harvard Medical School. Hundreds of thousands of people in these studies have been followed for decades. What they eat, and the diseases they develop, are carefully recorded.

These studies show that the average healthy person suffers no adverse health effects from eating an egg a day. However, the studies also indicate that people with diabetes or who already have heart disease probably should eat no more than three egg yolks per week. (Eating just the whites is fine.)

Be sure to cook the eggs until both the whites and the yolks are firm; undercooked eggs can transmit a bacterial infection that’s called salmonella.

Finally, my colleagues in the Department of Nutrition at Harvard’s School of Public Health point out that what you eat with your eggs is also important for your heart health. On their website they remind us that “salsa and a whole-wheat English muffin are a far different meal than cheese, sausages, home fries, and white toast.” It’s one of those obvious pieces of advice that’s easy to forget as you make, or order, breakfast. 

—Anthony L. Komaroff, M.D.
Editor in Chief
Harvard Health Letter

Posted by: Dr.Health

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