Good, Bad, or Ugly? What's the Deal with Eggs?

Explosive Egg

Eggs and their impact on human health represent one of the most controversial topics in the (healthy) nutrition literature. Egg yolk is a significant source of cholesterol—a medium-sized egg contains about 200 mg—which, when present in high serum levels, plays a key role in the development of atherosclerosis. It also contains choline, which is further metabolized into trimethylamine N-oxide (TMAO), a suspected risk factor for cardiovascular (CV) disease.

On the other hand, eggs contain many high-quality nutrients: proteins, all essential vitamins except for vitamin C, a range of minerals, and other bioactive compounds. An average egg provides about 62% of the recommended daily intake (RDI) of vitamin B12, 30% RDI of selenium, 16% RDI of iodine, and 12% RDI of vitamin D. All of this is packaged in a relatively low-calorie "bundle" (about 75 kcal), with a predominance of unsaturated fatty acids. Most nutrients are found in the yolk, while the egg white consists mainly of protein.

The relationship between egg consumption and the risk of various diseases (especially CV diseases, cancer, and type 2 diabetes) has been examined in numerous epidemiological studies. However, their results do not allow for clear conclusions.

We Don’t Know, But We Have a System

In recent years, several systematic reviews with meta-analyses of randomized controlled trials (RCTs) have summarized the available data. These have found significant heterogeneity among individual RCTs, with the number of eggs consumed in the intervention arms ranging from 5 to 42 per week.

The foods consumed in the control groups also varied greatly across individual RCTs, ranging from simply omitting eggs from the diet to replacing them with egg whites, lean meat, egg substitutes, or oatmeal. Overall, data from randomized evaluations suggest that egg consumption may have a mild effect on increasing serum cholesterol levels.

Let’s Observe and Analyze

The results of observational studies are conflicting, depending on the study population. In healthy individuals, a slightly positive or no effect on the risk of CV disease was generally observed. In patients with pre-existing diabetes, higher egg consumption was associated with increased CV disease risk.

A meta-analysis of 41 prospective cohort studies found that higher egg consumption was associated with an increased overall risk of CV events (risk ratio [RR] 1.04 per 50 g increase in daily egg intake). However, this correlation was observed primarily in studies conducted in the U.S. (RR 1.08), but not in European (RR 1.05) or Asian studies (RR 0.96).

Another meta-analysis, on the contrary, found a negative correlation between consuming up to 7 eggs per week and the risk of non-fatal CV events (RR 0.94 compared to avoiding eggs). Among people consuming up to 3 eggs per week, a reduced risk of non-fatal ischemic heart disease was also observed compared to those who consumed no eggs (RR 0.92).

What Are We Actually Comparing?

A major limiting factor of observational study meta-analyses is that they rarely consider what eggs are being replaced with in the diet. Therefore, if an analysis concludes that higher egg consumption is associated with increased disease risk, we must ask: Compared to what?

For example, the aforementioned meta-analysis performed regression modeling of mortality under different dietary patterns, where total caloric intake and macronutrient proportions—carbohydrates, proteins, and fats—were comparable. The risk of death from CV disease was higher among those consuming 300 mg of cholesterol daily from food, compared to those with zero dietary cholesterol intake (hazard ratio [HR] 1.13).

If the comparison was between a person consuming one egg per day and a person who did not replace the egg with any other food, the risk remained slightly elevated (HR 1.09). However, if the egg were replaced with a food of similar caloric value that also contains cholesterol—such as dairy products, processed meats, fish, red meat, etc.—the CV risk associated with eating one egg would actually be lower (0.92).

So, Should We Eat Eggs or Not?

Available data clearly indicate that the body’s response to dietary cholesterol is individual. On average, about 56% of dietary cholesterol is absorbed, but this value ranges from approximately 29–80% among individuals. This is influenced by genetic variability of cholesterol receptors and individual differences in liver metabolism.

Foods that are sources of cholesterol often also contain saturated fatty acids, which negatively affect LDL cholesterol levels in the blood. However, this is not the case with eggs.

The data suggest that eggs have a generally positive or neutral impact on health, and if regularly consumed as part of a balanced diet, they should not pose a health risk. They contribute to satiety and may have a myoprotective effect, which could help maintain optimal body weight. Moreover, they appear to be one of the most environmentally sustainable sources of animal protein.

Editorial Team, Medscope.pro

Sources:

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