Throughout history—even before fowl were domesticated some 8,000 years ago—humans ate eggs, wherever they could find them. An excellent source of protein and easy to obtain, cook, and incorporate into recipes, eggs hit a bump in the road in the 1970s, when concerns arose that they raise blood cholesterol. In fact, in the 1980s, average U.S. egg consumption dropped from two or three a week to one or two a week.
But research in more recent years has largely exonerated eggs and even suggested that they may provide some heart (and other) benefits.
Cholesterol: not a deal breaker
Eggs have had a bad reputation because of their high cholesterol content: 185 milligrams in the yolk of a large egg. But, in fact, dietary cholesterol, found in animal foods, has relatively little effect on blood cholesterol in most people—saturated and trans fats are the bigger culprits.
And even in people who do respond to dietary cholesterol, some egg studies have shown that dietary cholesterol causes the body to increase HDL (“good”) cholesterol along with LDL (“bad”) cholesterol, possibly helping to offset adverse effects. Moreover, the LDL particles that form are larger in size—and larger LDL particles are not as strongly linked to plaque in blood vessels as small ones are.
A small University of Connecticut study, published this year in the Journal of Nutrition, found that when healthy young adults went from no eggs to three eggs a day, they had increases in large-sized LDL particles, as well as improvements in HDL composition, which makes it more effective in removing cholesterol from cells.
In earlier research from the University of Connecticut, eating three eggs a day for 30 days increased cholesterol in some people, but their LDL particles were larger, and there was no change in the ratio between LDL and HDL, which suggests no major change in coronary risk. Including eggs in a carbohydrate-restricted diet also leads to increased HDL, according to these same researchers.
Cardiovascular surprises
More significantly, eggs do not appear to contribute to heart disease. A pivotal study from Harvard in 1999, of nearly 120,000 people, found no association between egg intake—up to seven a week, on average—and heart disease, except perhaps in those with diabetes. Nor did it find a link between eggs and strokes.
Studies since then have continued to vindicate eggs. For example, a study in 2016 in the American Journal of Clinical Nutrition looked at more than 1,000 middle-aged Finnish men and found that neither egg intake (one a day, on average) nor cholesterol intake was associated with an increased risk of coronary heart disease. This was true even among those who had a particular genetic factor that affects cholesterol metabolism and therefore put them at higher risk. There was also no significant impact on the thickening of the carotid artery (the main artery going to the brain), which is an indicator of hardening of the arteries (atherosclerosis).
Similarly, an analysis of eight observational studies, published in 2013 in BMJ, found no relationship between eggs (up to one a day, on average) and heart disease or stroke in half a million people who were followed for 8 to 22 years.
More recently, an analysis of seven studies, published in the Journal of the American College of Nutrition in 2016, found that people who had a high egg intake (generally considered seven a week) had a 12 percent reduced risk of stroke compared with those who had a low egg intake (less than two eggs a week), after the researchers accounted for such variables as smoking, age, sex, and exercise in most of the studies.[inset:3989]
The diabetes dilemma
Studies on the relationship between eggs and heart disease in people with or at risk for type 2 diabetes have been inconsistent, resulting in somewhat murky recommendations. As the author of an “expert analysis” from the American College of Cardiology noted in 2015, “People with diabetes may represent a special population for whom attention to dietary cholesterol intake and egg consumption does make sense, at least until further research provides more clarity.”
In contrast, a review in the journal Nutrients, also in 2015, concluded that the evidence suggests that eggs—even at amounts higher than what’s recommended in some countries—are safe as part of a healthy diet, not only for the general population, but also for those with type 2 diabetes, as well as those who have or are at risk for cardiovascular disease.
And this year, a review of six randomized controlled studies, published in the Canadian Journal of Diabetes, found that eggs—6 to 12 a week, in the context of a heart-healthy diet—did not raise LDL cholesterol, triglycerides, or blood-sugar measures in people with or at risk for diabetes.
A change of heart
In light of these accumulating findings, recommendations about eggs have changed over the years, and the latest Dietary Guidelines for Americans no longer include an upper limit for cholesterol intake (it had been 300 milligrams a day for healthy people, lower for those with diabetes and other risk factors). In fact, the guidelines specify that a healthful eating pattern embraces a variety of protein foods, including eggs.
Here’s when good eggs go bad: When they are fried in lots of butter or accompany foods like bacon, sausage, cheese, and biscuits (as in a typical American breakfast), they can raise blood cholesterol and the risk of heart disease, since these foods are high in saturated fats, which boost LDL cholesterol. For instance, while a medium egg has only 1.5 grams of saturated fat, 72 calories, and 70 milligrams of sodium, a Bacon, Egg & Cheese Biscuit from McDonald’s has 12 grams of saturated fat, along with 450 calories and 1,290 milligrams of sodium.[inset:3964]
Does TMAO spell trouble?
Egg yolk is one of the richest sources of choline, a vitamin-like essential nutrient. That has always been considered a nutritional plus, but researchers have discovered that choline from eggs (and supplements) interacts with intestinal microbes to form TMAO (trimethylamine N-oxide), a compound associated with an increased risk of heart disease and stroke. (Carnitine in meat causes the same reaction.)
In a small dietary intervention study in the American Journal of Clinical Nutrition in 2014, eating two or more egg yolks a day led to TMAO formation, though there were great individual differences. In contrast, a 2017 study in the FASEB Journal found that blood levels of TMAO did not increase in people who ate up to three eggs a day for four weeks (though their choline levels went up).
Are choline and TMAO a reason to avoid eggs? We don’t think so, since eggs provide many beneficial compounds. Moreover, choline is also found in many heart-healthy foods, such as salmon, sardines, beans, and broccoli. Keep in mind, too, that there is still some debate about the association between TMAO and health risks; further research is in progress.[inset:3990]
Bottom line
Many egg studies have been funded by the egg industry or have researchers associated with it. And clinical trials, as opposed to observational studies, have lasted only a few weeks or months, so the long-term effects of eating a lot of eggs have not been established.
It’s also not clear how various genetic factors as well as the gut microbiome interact with the effects of egg consumption, for good or bad. Still, eggs are good food, and most people can eat one a day (the equivalent of seven a week), or perhaps more, without ill effects—and possibly with benefits. The key is not to muck them up by preparing them with lots of fatty and salty ingredients and not to regularly accompany them with unhealthy side dishes.
People who have diabetes may still need to be watchful of their egg and cholesterol intake, however, and should discuss this with their doctors.