People who eat seven or more eggs per week have almost double the rate of arterial damage as those who eat one egg or less per week, according to a study in Atherosclerosis (June 3, 2015). The egg-eaters who were overweight or did not eat a lot of vegetables had the largest accumulation of plaques in their arteries.
In this study, 23,417 healthy men and women with no history of heart disease had a test called cardiac computed tomography (coronary artery calcium) to measure the size and shape of plaques in their arteries. For each increase of one egg per day, there was a 54 percent increase in plaques in arteries leading to their hearts.
Nobody really knows if eggs increase risk for heart attacks. A major flaw in most studies on eggs is that many North Americans consume their eggs WITH processed meats (bacon and eggs, ham and eggs, sausage and eggs). I have never seen a study on eggs that corrects for this, so any reported harm may come from the added servings of processed meats rather than from the eggs.
How Plaques Increase Heart Attack Risk
Some studies show an association between egg consumption and heart attacks, while others show no association. This study associated the number of eggs that a person eats with the amount of plaques in the arteries leading to a person's heart.
The first step leading to a heart attack is the formation of plaques in arteries. When part of a plaque breaks off from the inner wall of an artery, a clot forms over the spot where the plaque was removed. The clot can extend to block off blood flow completely through that artery, so the part of the heart muscle supplied by that artery gets no blood flow, depriving it of oxygen so the muscle dies, which is a heart attack. The more plaque a person has in the arteries leading to his/her heart, the more likely he/she is to suffer a heart attack.
Dietary Cholesterol is Not the Culprit
Eggs contain cholesterol, but most scientists no longer believe that dietary cholesterol causes heart attacks, even though people who have high blood levels of cholesterol are at increased risk for a heart attack. Your body makes cholesterol whether you eat it in your diet or not. Long before a plaque forms in an artery, small holes appear in the inner linings of an artery that leak blood to forms clots.
Only when the holes start to heal does cholesterol start to form plaques in the artery. Cholesterol does not even appear in an artery until long after the damage starts. Sugar molecules are found in the holes in arteries that precede the formation of plaques, so sugar may be one of the causes of these holes.
The TMAO Theory
Eggs yolks contain choline and lecithin that are converted by intestinal bacteria into another chemical called tri methyl amine oxide (TMAO), which can punch holes in the arteries of both humans and animals (The New England Journal of Medicine, April 25, 2013;368 (17): 1575–1584). TMAO may also cause high blood pressure (Canadian Journal of Cardiology, December 2014;30(12):1700–1705). The same bacteria also convert creatinine and carnitine to TMAO.
High concentrations of lecithin are in soy, eggs and some dietary supplements. Carnitine is in red meat, some energy drinks, and some dietary supplements. Eating a plant-based diet markedly reduces the number of intestinal bacteria that form TMAO (Nature Medicine, April, 2013;19 (5): 576–85). For a detailed explanation of TMAO, see my report on Why Meat Eaters Have More Heart Attacks
I believe that enough evidence exists to suggest that you should limit your consumption of egg yolks. The Physician's Health study showed that men who ate five or more eggs per week had a 50 percent higher risk for diabetes than those who did not eat eggs, and women who eat more than six eggs per week had a 77 percent higher risk of diabetes (Diabetes Care, 2009;32:295). Men who ate 2.5 eggs per week had an 81 percent higher risk of dying of prostate cancer than those who ate less than an egg per week (Cancer Prev Research, 2011;4:2011).
I personally do not eat eggs. My breakfast contains oatmeal made with water and raisins. However, eating one egg per day may be less harmful than the typical breakfast of dry cereal with sugar and other refined carbohydrates, which can increase risk for diabetes, heart attacks, and certain cancers (Am J Clin Nutr, March 9, 2010;91(3):502-9).
If you do eat eggs, make sure that you also eat plenty of vegetables that reduce the amount of intestinal bacteria that convert egg yolk lecithin and choline to the potentially harmful TMAO. Also avoid pairing your eggs with processed meats.
Gabe Mirkin, M.D., is a sports medicine doctor and fitness guru. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin has run more than 40 marathons and is now a serious tandem bike rider with his wife, Diana, often doing 30-60 miles in an outing. His website is http://drmirkin.com/.