Is eating eggs a health risk?

Dr Derrick Aarons

Sunday, July 09, 2017

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IN recent times, there has been some controversy regarding whether people should be eating eggs or not.

This has occurred as the evolution of science and scientific knowledge from ongoing research has altered many things we once believed to be factual and causing doubt on some others for which we now require more research. Scientists generally make informed decisions based on the evidence that exists at a point in time, but as more evidence emerges from the ever-expanding areas of research, the recommendations made from the new emerging evidence may change over time.

The recommendations to be made regarding the consumption of eggs are now at such a crossroads. Two research studies that evaluated the use of eggs in the diet concluded that consuming an egg per day actually doubled the risk of coronary heart disease among Americans who became diabetics during the follow-up period. Yet another study — conducted in Greece where individuals eat a predominantly Mediterranean diet that is regarded as among the healthiest in the world — indicated that eating an egg each day increased the risk of a coronary heart attack five-fold.

A source of cholesterol

The consensus is that the yolk of the egg is a huge source of cholesterol, and excess cholesterol is harmful as the excess tends to deposit along the blood vessels of the body. When it does so along the narrow vessels of the heart, a reduced blood flow to the heart muscle can occur and thus produce angina chest pain.

When the cholesterol deposits result in total blockage, then a heart attack occurs. The excess cholesterol will also deposit along the blood vessels of the brain, and when there is a drastic reduction of oxygen flow to the brain, a stroke can occur.

At the World Stroke Congress in 2016, quotations from the 2015 US Dietary Guidelines stated that there was not sufficient data to recommend a daily target or limit of cholesterol consumption. However, the cholesterol intake should be as low as possible within the recommended dietary pattern. Further, the white portion of the egg is a good source of protein and so should be used instead of the yellow egg yolk, where all the cholesterol is concentrated.

Warning from doctors

Doctors may warn patients who have partial blockage of their heart vessels to stop eating eggs, but to stop eating eggs after having had a heart attack is akin to stopping smoking after a diagnosis of lung cancer has been made.

Research has shown that eggs are a common source of cholesterol in the diet, and a single large egg contains as much as 186 mg of cholesterol. However, egg also contains other vital components, such as protein and essential fatty acids, and so an egg should be evaluated not for a specific constituent part, but rather on the total consumption of all its ingredients.

Paradoxically, the 2015 Dietary Guidelines for Americans state that the currently available evidence shows no relationship between consumption of dietary cholesterol and the level of cholesterol in the blood. Consequently, it opined that cholesterol was not a nutrient of concern with regards to its over-consumption.

New research

Researchers working in this field subsequently searched through the medical literature and found several newer studies that prompted their comprehensive review of all related publications to estimate any associations between the intake of eggs and the outcome of cardiovascular disease. This systematic review methodology puts all the evidence together and synthesises all the data across numerous studies in order to make an informed decision on the body of epidemiological literature and what it says on the subject. Some of the studies found were conducted in the USA, Japan, Australia, Spain, and the United Kingdom.

Interestingly, the results indicated that the relative risk for a stroke occurring in individuals who ate one egg per day compared to those who ate fewer than 2 eggs per week was very low. In other words, whether you ate fewer than two eggs per week or as much as one egg per day, your egg-eating habit was unlikely to contribute much in regard to you having a stroke. In fact, eating up to three and a half eggs per week was associated with a significant reduction in the incidence of stroke.

Additional research necessary

The researchers found that the consumption of eggs did not lower the risk for heart disease, and did not increase the risk either. They said there were no clear dose-response trends found in either the 'meta-analyses or meta-regression analyses' for risk of coronary heart disease, and were consistent with two previous meta-analyses of egg consumption and cardiovascular disease, coronary heart disease, and stroke.

The researchers admitted, however, that because the data came from cohort studies (research observing people over a period of time), there was no way to assess whether people with a higher egg intake might have engaged in favourable lifestyle habits that could have contributed to the favourable results. Consequently, additional research will be necessary to give us clear guidance regarding the consumption of egg yolk and any risk for health.

Derrick Aarons MD, PhD is a consultant bioethicist/family physician, a specialist in ethical issues in medicine, the life sciences and research, and is the Ethicist at the Caribbean Public Health Agency – CARPHA. (The views expressed here are not written on behalf of CARPHA)




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