No Free Brunch? Eggs Once Again Feel the Scramble in New, Large Observational Study

Even half an egg per day, on average, is linked to greater risk of cardiovascular disease and all-cause death over the long term, according to a new observational study of nearly 30,000 people. And, reawakening a decades-old controversy in this field, Victor W. Zhong, PhD (Northwestern University, Chicago, IL), and colleagues say it’s the cholesterol, not the eggs per se, that likely shoulders the blame for this increased risk.

Their analysis was published last week in JAMA.

Whether eating too much cholesterol actually causes CVD remains a controversial topic, they acknowledge. Also, “It is unclear whether eating an overall high-quality diet attenuates the associations of dietary cholesterol consumption with CVD and mortality or if the food source of cholesterol (eg, eggs, red meat, poultry, fish, and dairy products) is important.”

Zhong told TCTMD via email that, while the results can’t prove causation, they should inspire a closer look at dietary advice.

“Eating less than 300 mg of dietary cholesterol per day was the guideline recommendation before 2015. However, the most recent 2015-2020 Dietary Guidelines for Americans no longer include a daily consumption limit for dietary cholesterol and recommend weekly egg consumption as part of the healthy US-style eating pattern,” Zhong noted. “Our study findings suggest a need to reevaluate the current US dietary guideline recommendations for dietary cholesterol and eggs.”

Our study findings suggest a need to reevaluate the current US dietary guideline recommendations for dietary cholesterol and eggs. Victor W. Zhong

To put things in perspective, he said, their data translate into 11 more people per 1,000 who will develop CVD and 19 more who will die within three decades if they consume an extra half an egg per day.

Commenting on the study for TCTMD, Mahshid Dehghan, PhD (McMaster University, Hamilton, Canada), a nutritional epidemiologist, expressed some skepticism about the study methods. She encouraged cardiologists to tell their patients that moderation is best. Specifically, other research has shown that up to one egg per day has no adverse effects, Dehghan advised. “It’s important to emphasize the amount of consumption.”

The More Consumed, the Higher the Risk

The investigators combined data on 29,615 people (mean age 51.6 years) from six US cohorts that collected self-reported diet measures between approximately 1985 and 2016. Around one-third of participants identified as black, and 45% were men. Median follow-up duration was 17.5 years, in which there were a total of 5,400 incident CVD events (fatal and nonfatal coronary heart disease, stroke, heart failure, and other CVD deaths) and 6,132 all-cause deaths.

Relationships between dietary cholesterol or egg consumption and CVD or all-cause mortality were consistent, with risk rising for each additional 300 mg of cholesterol and for each half an egg eaten per day. A large egg contains approximately 186 mg of cholesterol.

Adjusted for Demographic, Socioeconomic, and Social Factors

The more eggs eaten, the higher the risk. For example, the adjusted hazard ratios for people who consumed two eggs daily were 1.27 (95% CI 1.10-1.45) for CVD and 1.34 (95% CI 1.15-1.52) for mortality.

Yet after adjusting for the consumption of dietary cholesterol, eggs in and of themselves no longer carried extra risk—in other words, the cholesterol is the larger problem. Further analyses that adjusted for the combination of eggs, red meat, and processed meat eliminated the added risk associated with dietary cholesterol, suggesting that these food sources are important contributors of cholesterol to the diet.

Controversy Continues

Robert H. Eckel, MD (University of Colorado School of Medicine, Aurora), in an editorial accompanying the paper, observes that the topic is “important to clinicians, patients, and the public at large because the association of egg consumption and dietary cholesterol with CVD, although debated for decades, has more recently been thought to be less important. Compared with the meta-analyses and reviews previously published, this report is far more comprehensive, with enough data to make a strong statement that eggs and overall dietary cholesterol intake remain important in affecting the risk of CVD and more so the risk of all-cause mortality.”

Although the associations are modest, they are relevant on a population level, he stresses, adding that the overall message is to limit intake of cholesterol-rich foods.

The harm that we’re observing may be confounded by sugar or carbohydrates. Mahshid Dehghan

Dehghan, for her part, cited several examples of what she thinks are flaws in the analysis.

Food frequency questionnaires, for instance, were not designed to capture exact amounts of what individuals eat (eg, half an egg) but rather to compare consumption across individuals, Dehghan explained. Also, the diets were measured as far back as 30 years ago as events continued to accrue. “People change their diet during 30 years—it’s a long period of time,” she stressed. Further, many studies have shown only weak correlations between dietary cholesterol and blood lipids, and details on the latter weren’t included in the current analysis.

“The other thing is when they did the adjustment, they didn’t adjust for starchy foods, processed foods, pastries, sugar,” Dehghan pointed out. Many people get their eggs from cakes and other baked goods, where sugar is also a key ingredient. She suggested that “the harm that we’re observing may be confounded by sugar or carbohydrates.”

Another thing to keep in mind is that on a worldwide scale, egg consumption is quite low and that there’s no one-size-fits-all advice, Dehghan observed. People in low- or middle-income countries and those living in high-income countries like the United States but who are poor “need to consume eggs, because of the quality of the protein. . . . When you encourage [people] to reduce their egg consumption, they increase their starchy food consumption” in order to get enough calories, she commented.

Zhong, too, noted in his email that the new results “may not be applicable to populations from other countries, particularly those from low- and middle-income countries that have a different food supply and different obesogenic and atherogenic environment from the US.”