By HENRY DERRICK
April 1st, 2019
A new study has just rekindled the debate on whether or not eggs are healthy. According to its findings, the more eggs you eat, the higher your risk of heart disease and premature death.
Results of previous research suggest the opposite, finding that eggs are not linked to increased risks of cardiovascular disease or stroke.
Some experts raise concerns about the study itself, bringing up points that show the findings may not be as clearcut as some media reports are making them seem.
Perhaps even more than red meat, coffee, or wine, egg yolks seem to elicit debate over whether they’re a power-packed source of vitamins and protein, or a heart-attack fuse just waiting to be lit.
A new study takes the latter position. After analyzing data on nearly 30,000 adults from six studies spanning 31 years of follow-up, researchers concluded that eating 300 milligrams (mg) of dietary cholesterol per day—one egg yolk, in comparison, provides 185 mg—raises incident cardiovascular disease by 17 percent and early death by any cause by 18 percent.
Eating just three to four eggs per week was associated with a 6 percent higher risk of cardiovascular disease and 8 percent higher risk of any cause of death. And if you eat two eggs per day, you’d be boosting your risk of cardiovascular disease by 27 percent, and your risk of early death by 34 percent, according to the study.
In the study, higher egg consumption had these associations regardless of age, activity levels, race, smoking status, blood pressure, or cholesterol levels.
“Our study does not suggest there is a safe amount for egg consumption,” lead researcher Wenze Zhong, Ph.D., in the Department of Preventive Medicine at the Feinberg School of Medicine at Northwestern University, told Runner’s World. “Any level of egg consumption is associated with increased risk of cardiovascular disease and mortality because we found a dose-response association. Greater consumption means higher risk.”
Is the new study all it’s cracked up to be?
The debate over eggs originated because of yolks’ high cholesterol content, and previous recommendations cautioned people to eat less cholesterol as a way to prevent cardiovascular disease, according to Alyssa Pike, R.D., manager of nutrition communications at the International Food Information Council.
However, she told Runner’s World, daily cholesterol limits were removed from the U.S. government’s 2015 Dietary Guidelines for America.
“This change came about because the current body of research about dietary cholesterol does not support the idea that dietary sources of cholesterol have a large impact on our blood cholesterol levels,” she said.
Stuart Phillips, Ph.D., the director of the McMaster Centre for Nutrition, Exercise, and Health Research, agrees that the cholesterol-from-food link may not be as damning as we once thought.
“Cholesterol may be something to pay attention to, but its relationship to heart disease and death isn’t huge, and there are lots of other contributors,” he said. “Even the paper itself shows that it isn’t really the problem.”
In fact, the study itself may have some issues—something important to address before drawing any sweeping dietary conclusions from its findings.
For one, the amount of risk, or hazard, that’s reported here is trivial—and the way in which they calculated it doesn’t exactly lend itself to an easy determination of someone’s true risk, Phillips said.
He added that the authors themselves admitted there were significant limitations.
In that acknowledgment, the researchers noted there may be measurement error because the diet data was based on recall—for example, imagine that someone just asked you, “Exactly how many eggs did you have last month?” Not only can this type of self-reported data be unreliable, but also researchers assessed this only once, Phillips pointed out and assumed it didn’t change in an average of 17 years of follow-up.
Also, they stated that all cohorts used different dietary assessment tools, leading them to implement their own methodology to harmonize diet data. Finally, the study findings are observational, so while they can suggest a relationship, they can’t prove that one thing caused the other.
Now, the last point isn’t surprising, since nearly all nutrition studies are observational, and most rely on self-reported data, said Andrew Mente, Ph.D., principal investigator for the Epidemiology Program at the Population Health Research Institute. After all, it’s tough to find a large number of research participants willing to eat a very restricted diet for decades, simply so you can try to find potential health associations. But, Mente told Runner’s World, there are several problems with the paper that go beyond the correlation-doesn’t-equal-causation issue.
“The primary hypothesis here is that eggs increase your bad cholesterol, and the more you eat, the worse it gets,” he said. “But buried way down in the appendix is a note that they found higher egg intake is related to a reduction in LDL, your bad cholesterol. So, what’s driving the association in this research? It seems like there’s a contradiction with the findings.”
Another ping against the study, he added, is that the findings don’t agree with other notable cohort studies—which is research done over a period of time, with researchers checking in at certain intervals. That includes studies like this one, and this one, and this one, and this one, the findings of which all conclude that there is no increased risk of coronary heart disease or stroke with higher consumption of eggs, usually defined as one egg per day.
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So should we really shelve eggs?
That’s a whole lot of information to take in when you’re considering what you should put on your plate for breakfast this morning. Should you use this study’s findings to change your habit?
You might not need to stop cracking those eggs yet. With the potential issues outside experts raised about the paper—and the fact that other previous studies have arrived at opposite conclusions—changing how you eat based on the results of one study may be premature.