Here we go again. Everything “bad”—butter, red meat, cheese—is good again, and everything “good”—whole grains, fruit—is bad again. The constant seesawing between demonization of a particular food one day and its vindication the next appears to be the unfortunate result of the electronic age, where media outlets compete for likes and shares, and will put just about anything in a headline to get consumers to click on a story. To use alcohol consumption as an example, this happens on a nearly daily basis: One headline warns, a “daily glass of wine increases risk of early death by 20%,” while another says, “having a drink may help you live longer.” With this in mind, let’s look at a recent study claiming to show a dose-dependent association between higher consumption of eggs or dietary cholesterol and greater risk of incident CVD and all-cause mortality.
The study, Associations of Dietary Cholesterol or Egg Consumption With Incident Cardiovascular Disease and Mortality, was published in JAMA last month, and it caused quite a stir, particularly among low-carb, Paleo, and ketogenic dieters, many of whom may be consuming more eggs than they did in the past, yet have experienced impressive improvements in longstanding health problems and have markedly improved cardiovascular disease risk profiles.
According to study co-author Norrina Allen, “Our study showed if two people had exact same diet and the only difference in diet was eggs, then you could directly measure the effect of the egg consumption on heart disease. […] We found cholesterol, regardless of the source, was associated with an increased risk of heart disease.”
It must be noted, however, that this study was based on self-reported food intake, a method that has been questioned by many. A paper in the journal Frontiers in Nutrition exploring the weaknesses of this type of data went so far as to state that self-reported dietary intake has engendered “a fictional discourse on diet-disease relations driven by decades of deeply flawed and demonstrably misleading epidemiologic research.”
Study participants were asked about the foods they’d consumed during “the previous year or month.” The study authors acknowledged that it’s a major limitation that participants’ long-term eating patterns weren’t assessed: “We have one snapshot of what their eating pattern looked like. […] But we think they represent an estimate of a person’s dietary intake. Still, people may have changed their diet, and we can’t account for that.” Indeed. Anyone who’s made a radical shift in diet, such as adopting a Paleo, ketogenic, or vegan diet—will have a dramatically different dietary intake compared to what they would have reported months or years before the switch. So, if an association is identified between current egg or cholesterol consumption, is it due to the eggs someone regularly consumes now, or due to whatever types of foods they were consuming for years, possibly decades, before?
The JAMA study used data pooled from 6 prospective cohorts (data collected between March 1985 and August 2016) and found that eating three to four eggs per week was associated with a slightly higher risk for CVD and all-cause mortality. It’s difficult to reconcile this with other research, such as a paper that stated: “To date, extensive research did not show evidence to support a role of dietary cholesterol in the development of CVD. As a result, the 2015–2020 Dietary Guidelines for Americans removed the recommendations of restricting dietary cholesterol to 300 mg/day.”
Other research—admittedly also based on self-reported food intake, but why not fight fire with fire—concluded that daily egg consumption (among Korean adults) decreased the prevalence of abdominal obesity and consuming eggs 4-7 times a week was associated with lower prevalence of metabolic syndrome, which is a major driver of CVD.
A meta-analysis and prospective cohort study in China found no significant difference in all-cause mortality between subjects who consumed more than 7 eggs per week and those who consumed less than 1 egg per week. In fact, the highest egg consumption was associated with a small decrease in risk for stroke. A separate Chinese study determined that compared to no egg consumption, daily egg consumption was associated with lower risk of CVD and hemorrhagic stroke death. Again, these were based on frequency questionnaires, but the point is, if fearmongering headlines are going to be published about egg consumption and increased risk for CVD and all-cause mortality, an equal number of headlines could be published that show the exact opposite.
The decades-long demonization of eggs—which began in 1968 and persisted until 2015—appears to be making a comeback, despite the lack of a plausible mechanism by which dietary cholesterol, or even serum cholesterol, may be a singularly causal factor in CVD. New headlines about the “risks” of eating eggs might lead people away from an affordable, highly digestible and complete source of protein, choline, lutein, and other important nutrients. There’s no “requirement” to consume eggs, so people can avoid them if they wish, but those who enjoy omelets or egg salad should take heart knowing that “half a century of research have shown that egg and/or dietary cholesterol intake is not associated with increased CVD risk.”