Eating egg yolks could have a similar—and almost as harmful—impact on your arteries as smoking, according to a study published last year in the journal Atherosclerosis. Both activities had similar effects on the development of atherosclerosis, a buildup of plaque on arterial walls that can increase a person’s risk of heart attack and stroke.
The study was headed by Dr. J. David Spence, a professor of neurology at Western University in Canada. Spence and a team of researchers worked with 1,231 middle-aged patients who had visited a vascular prevention clinic at the London Health Sciences Centre's University Hospital after having a stroke or a "mini-stroke."
The scientists polled the patients about their egg yolk consumption, smoking, exercise habits and other lifestyle factors, and measured subjects' carotid wall thickness.
When the researchers compared the numbers, they saw that the top 20 percent of egg consumers had carotid arteries that were two-thirds as impaired as those of smokers.
Some scientists were not sold on the findings, however, saying that the comparison is difficult to make, as smoking and egg yolks harm the body in different ways.
"Smoking has a direct effect on blood vessels and development of plaque, whereas with eggs, it's really an indirect effect: Eggs are part of the diet and the diet has an effect on overall blood cholesterol," Dr. David J. Frid, a staff cardiologist in preventive cardiology at the Cleveland Clinic, told The Huffington Post. "A high level of blood cholesterol can lead to arterial plaque, but there are so many factors that can affect your cholesterol above eating eggs. There's the rest of your diet, whether you're overweight, whether you exercise, genetics."
Spence said he and his team did not have the data to consider overall dietary patterns.
The reason for the correlation, Frid suggested, was that the number of egg yolks eaten could be an overall indicator of a high-fat, high-cholesterol diet that can cause atherosclerosis. In this way, poor eating habits—rather than egg yolks alone—would be the reason behind plaque buildup.
Other critics agreed, saying the study did not account for other dietary factors that can affect cardiovascular risk, including saturated and trans fats, as well as dietary fiber.
To make the matter even more complicated, a large earlier study found that eating whole eggs was associated with a rise in good—and not just bad—cholesterol.
While the verdict on egg yolks may still be out, the safest approach is to follow dietary guidelines from the National Heart, Blood, and Lung Institute. According to the organization, one yolk has two-thirds of the recommended daily cholesterol intake for healthy individuals without heart disease, diabetes or high LDL-cholesterol. If you go by these guidelines, you should eat just four whole eggs per week.