Eggs are bad – then good – then bad again? What gives?

March 15 2019 by in Bad science, Cholesterol, Heart disease, New study

Do you eat exactly the same as you did in 1985? Do your friends, family and colleagues eat the same way they did?

If so, then the latest study suggesting eggs are harmful may be of interest to you.

JAMA: Associations of dietary cholesterol or egg consumption with incident cardiovascular disease and mortality

But for the overwhelming majority of the population who do not maintain absolute dietary consistency for decades, the new study likely has little relevance.

Unfortunately, that isn’t going to stop media coverage from claiming this new study shows that eggs increase the risk for heart disease and death, a topic that has remained controversial for decades.

The New York Times: Are eggs bad for your heart health? Maybe

Newsweek: How many eggs should I eat? Huge study links dietary cholesterol to heart disease

Initially maligned as harmful, the ACC/AHA dietary and lifestyle guidelines did an about face in 2013, admitting that dietary cholesterol found in eggs and shellfish was “no longer a nutrient of concern.” This came on the heels of studies showing no associative risk with increased egg consumption. Yet, that hasn’t stopped the debate.

The new study in question, published in the journal JAMA, was a massive statistical undertaking. The authors retrospectively analyzed previously obtained data from six different studies including almost 30,000 subjects. They crunched all the data between 1985 and 2016, with an average follow up of 17 years, and concluded higher egg consumption was associated with an increased risk of heart disease and death.

On the surface, this appears to be an impressive study. A large sample cohort, lengthy follow up, and important outcome measures such as all-cause mortality as well as heart disease events.

Looking deeper, however, we see that the subjects provided only one food frequency questionnaire at the time of enrollment. That’s it. One data sample to estimate dietary habits in 17 years of follow-up.

The entire study is based on an unreliable food frequency questionnaire given one time only with absolutely no consideration of how patients’ diets may have changed over 17 years.

Does that sound like good science to you? Is it possible that people drastically altered their eating habits, other lifestyle activities, or other health parameters over 17 years? I would venture to say, “Yes, it is.”

The paper tries to statistically explain the increased risk of cardiovascular disease with each 300 mg of dietary cholesterol (odds ratio 1.17 which is a very weak association) or for each half-egg consumed (1.06, an even weaker association). The problem, however, is that any conclusions drawn from incomplete and inaccurate data has no relevance to a scientific discussion. Furthermore, we know that such weak associations in retrospective observational trials are more likely to be from statistical error than an actual causative association (see the Diet Doctor policy for grading scientific evidence).

In the end, the JAMA study represents all that is wrong with nutritional research. Incomplete data, weak associative findings, lack of control for “healthy user bias,” confounding variables, and an over-reactive media culture that promotes such data as medically important.

At DietDoctor.com, we will continue to point out the flaws in these studies, and how they are unlikely to meaningfully contribute to any health or scientific discussion. We just hope the scientists and media will start listening!

Thanks for reading,
Bret Scher, MD FACC

Cholesterol and low-carb diets

Guide Read this guide to learn what cholesterol is, how your body uses it, why low-carb and keto diets may lead to a change in blood cholesterol levels, and whether you should be concerned if your cholesterol increases with a keto or low-carb lifestyle.

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