For decades, eggs were seen as coronary landmines because of their high cholesterol content (185 milligrams in the yolk of a large egg). But in recent years, eggs’ reputation improved as accumulating research suggested that dietary cholesterol, found only in animal foods, has little effect on blood cholesterol in most people—saturated fat is the main culprit. And even in people whose LDL (“bad”) cholesterol does rise in response to dietary cholesterol in eggs, some studies found that this does not increase the risk of heart attacks and strokes. Even if they have not been totally egg-xonerated, the charges against eggs seemed to be on the verge of being dropped.
Eggs got a boost from the 2015–2020 Dietary Guidelines for Americans, which dropped the longstanding daily limit of 300 milligrams of dietary cholesterol. But the guidelines still state that “individuals should eat as little dietary cholesterol as possible while consuming a healthy eating pattern.” One reason for this is that foods high in cholesterol, such as fatty meats, also tend to be high in saturated fat. Eggs are not high in saturated fat, however.
The latest headline-making twist in the egg-and-cholesterol saga was a major study published in the Journal of the American Medical Association in March 2019. The analysis pooled data from six well-known large cardiovascular studies involving 29,615 adults (average age 52), who were followed for up to 30 years (17.5 years, on average).
Over the course of the studies, each additional half egg consumed daily (that is, 3 or 4 eggs a week, slightly more than the average intake) was associated with a 6 percent increased risk of cardiovascular disease and an 8 percent higher mortality rate. Each additional 300 milligrams of cholesterol a day (mostly from meat and eggs) was associated with a 17 percent increased risk of cardiovascular disease and an 18 percent higher mortality rate. Risks were higher in women than men. The researchers controlled for many medical, dietary, and lifestyle factors. They concluded that the risk posed by eggs was fully due to their cholesterol content and that even people with “high-quality” diets were affected.
There were major problems with this study, however, which are all too common in such nonrandomized observational diet studies.
- The biggest problem: Dietary intake was determined by a single food questionnaire done at the start of each study, sometime between 1985 and 2005. Even if participants recalled their food intake accurately (a big if), their diets may well have changed over the next two decadesor so (hasn’t your diet changed since 2000?).
- Increased risks of 6 to 8 percent, associated with each additional half egg consumed a day, are “modest” (the authors’ word). In the context of such soft-boiled observational research, I’d say it’s too close to zero to be of practical significance.
- An increased risk of 17 percent associated with each additional 300-milligram-a-day rise in dietary cholesterol intake is more substantial, but that’s a big increase when compared to participants’ average daily cholesterol intake of 285 milligrams. In any case, eggs contributed only about 25 percent of that.
- Being an observational study, it only found associations and didn’t prove causality. Despite the researchers’ attempts to control for nearly all conceivable variables, they admitted that “residual confounding” was likely. That is, some unidentified habits or other factors might explain why people who ate a lot of eggs or dietary cholesterol at one point in time two decades ago had higher subsequent risks.
In light of all the uncertainty with this study and with egg research in general, we stick with our longstanding advice. Eggs are good food, rich in protein, vitamins, and minerals, but, as with animal foods in general, eat them in moderation. That means three to seven eggs a week for most people—somewhat more if you eat few or no other animal products.
This article first appeared in the UC Berkeley Wellness Letter.
Also see Eggs Make a Comeback.