Throughout history—even before fowl were domesticated some 8,000 years ago—humans ate eggs, whenever they could find them.
- Eggs are an excellent source of protein.
- Eggs are easy to obtain, cook, and incorporate into recipes.
Yet, eggs hit a bump in the 1970s, when concerns arose that they raise blood cholesterol. 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. It has even suggested that they may provide some heart (and other) benefits.
Cholesterol: not a deal breaker
Eggs developed a bad reputation over the years. That is because of their high cholesterol content.
- There are 185 milligrams in the yolk of a large egg.
- But, in fact, dietary cholesterol, found in animal foods, has little effect on blood cholesterol in most people.
- Rather, it is saturated and trans fats that are the primary culprits.
Even in people who do respond to dietary cholesterol, some egg studies have shown that dietary cholesterol causes the body to increase high-density lipoprotein (HDL “good”) cholesterol along with low-density lipoprotein (LDL “bad”) cholesterol. This might help to offset adverse effects. Also, the LDL particles that form are larger in size. These are not as strongly linked to plaque in blood vessels as small ones are.
- A small University of Connecticut study1 found that when healthy young adults went from no eggs to three eggs a day, they had:
- Increased large-sized LDL particles
- Improvements in HDL composition (more effective at removing cholesterol)
- In earlier research, 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. This suggests no major change in coronary risk.
- Including eggs in a carbohydrate-restricted diet also leads to increased HDL, according to these same researchers.
More significantly, eggs do not appear to contribute to heart disease.
- A pivotal observational study2 from Harvard in 1999 found no association between egg intake 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.
- A 2016 study3 found that neither egg nor cholesterol intake was associated with an increased risk of coronary heart disease.
- This was true even among those who had a genetic factor that affects cholesterol metabolism and puts them at higher risk.
- There was also no significant impact on the thickening of the carotid artery (the main artery going to the brain). This is an indicator of hardening of the arteries (atherosclerosis).
- Likewise, an analysis4 of eight observational studies found no relationship between eggs (one a day, on average) and heart disease or stroke.
- An analysis5 of seven studies found that people who had a high egg intake (seven a week) had a 12% reduced risk of stroke compared with those who had a low egg intake (less than two eggs a week).
The diabetes dilemma
Studies on eggs and heart disease in people with or at risk for type 2 diabetes have been inconsistent. This has resulted in somewhat murky recommendations.
- As an author6 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 of studies7 concluded that the evidence suggests that eggs are safe as part of a healthy diet. And they are safe not only for the general population, but also for those with type 2 diabetes. They are also safe for those with or at risk for heart disease.
- A review of six randomized controlled studies8 found that eggs—6 to 12 a week, with a heart-healthy diet, for people with or at risk for diabetes—did not raise:
- LDL cholesterol
- Blood-glucose measures
A change of heart
In light of these findings, recommendations about eggs have changed over the years. 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.) The guidelines now state that a healthful eating pattern embraces a variety of protein foods. This includes eggs.
Here’s when good eggs go bad:
- When they are fried in lots of butter.
- When they come with foods like bacon, sausage, cheese, and biscuits.
- 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, a bacon, egg, and cheese biscuit from McDonald’s has 12 grams of saturated fat, along with 450 calories and 1,290 milligrams of sodium.
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.)
- A small study9 found that eating two or more egg yolks a day led to TMAO formation, though there were great individual differences.
- In contrast, a 2017 study10 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.
Words to the wise
- Many egg studies have been funded by or have researchers connected with the egg industry.
- 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 genetic factors as well as the gut microbiome interact with the effects of eggs—for good or bad.
- Still, eggs are good food. Most people can eat one a day, 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. It is also key to not 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.
- Gisella Mutungi. Journal of Nutrition, February, 2008.
- Frank Hu. JAMA, April, 1999.
- Jyrki Virtanen. American Journal of Clinical Nutrition, March, 2016.
- Ying Rong. BMJ, January, 2013.
- Dominik Alexander. Journal of the American College of Nutrition, October, 2016
- Karen Collins. American College of Cardiology, August, 2015.
- N. Fuller. Nutrients, September, 2015.
- C. Richard. Canadian Journal of Diabetes, August, 2017.
- Carolyn Miller. American Journal of Clinical Nutrition, September, 2014.
- Bruno Lemos. FASEB Journal, April, 2017.