Cracking The Code: The Health Risks of Consuming Eggs
Studies suggest that eggs raise risk of type 2 diabetes, cardiovascular disease and cancer
If you only read news headlines to decide whether or not to eat eggs, you’re most likely confused. Are they good for you? Terrible? Somewhere in between? Let’s take a look.
Starting in the 1970s, there was a focus on reducing dietary cholesterol. Eggs were considered dangerous, since they are the most concentrated source of cholesterol in the American diet. When it became more well-known that dietary saturated fat was a bigger determinant of fasting cholesterol levels than dietary cholesterol, the conventional thinking on eggs changed. However, there is more to eggs than their effects on fasting cholesterol levels.
Eggs: A mix of positives and negatives
On the up side, eggs provide several vitamins; on the down side, they contain animal protein, and have no fiber. More positives and negatives: They’re not very high in saturated fat, but they are high in cholesterol. They’re rich in choline, which is an essential nutrient we need in adequate amounts for brain health;1 however, too much choline may have negative health effects. Also, eggs may expose us to pollutants such as PFAS.
Eating one egg per day (or more) is linked to higher risk of death
In long-term studies that use deaths as an outcome, intake of more than one egg per day is often associated with greater risk. For example, a pooled analysis of 55 studies found a 7% higher risk of death from all causes, and a 13% higher risk of death from cancer, for each egg eaten daily, but no difference in risk of death from cardiovascular disease.2 Other recent meta-analyses have reported similar findings.3,4
Sources:
Egg intake moderates the rate of memory decline in healthy older adults
Egg and Dietary Cholesterol Intake and Risk of All-Cause, Cardiovascular, and Cancer Mortality: A Systematic Review and Dose-Response Meta-Analysis of Prospective Cohort Studies
Eating 2 eggs per week linked to increased risk of type 2 diabetes
While the studies investigating mortality suggested an increase in risk associated with only high intakes of eggs (one or more egg per day), for risk of type 2 diabetes, studies have suggested an increase in risk associated with just two to four eggs per week. In a pooled analysis of U.S. studies published in 2021, there was an 11% increase in diabetes risk associated with eating two to four eggs per week, and a higher risk (27%) for one egg or more per day.5
Similarly, a 2023 meta-analysis of studies that used substitution analysis to compare the contribution of different foods to type 2 diabetes risk, estimated that replacing one egg per day with an ounce of nuts would lead to an 18% reduction in risk of type 2 diabetes, as well as similar decreases in cardiovascular disease and death from all causes.6
Also, in people who have diabetes, egg consumption is linked to an increase in the risk of cardiovascular disease. A meta-analysis of 6 studies found a 69% increase in cardiovascular disease risk in patients with diabetes who eat one or more per day, compared to those who eat less than one egg per week.7
Questions have been raised about whether these associations – between egg consumption and type 2 diabetes, cardiovascular disease, or deaths – represent a true association with eggs, or whether eggs are acting as a marker of an overall poorer diet in these studies. Although these studies adjust for BMI, total calorie intake, and other potential confounding factors, the authors of these meta-analyses have noted that they found stronger associations between eggs and negative outcomes in subcategories of participants with lower quality diets or in U.S. studies, compared to studies conducted in Asia or Europe.5, 8-10
It’s possible that part of the association is related to different dietary patterns in the regions studied, since people eat so poorly here in the US. But although eggs may not be as bad as sugary cereals and commercial baked goods, they still are a food that is a health negative when compared to beans, nuts, seeds, vegetables, fresh fruits and intact whole grains. Eggs might be a better breakfast option than sugary cereal, but not nearly as good as a berry bowl with ground flax and chia seeds.
Sources:
Egg consumption, overall diet quality, and risk of type 2 diabetes and coronary heart disease: A pooling project of US prospective cohorts
Substitution of animal-based with plant-based foods on cardiometabolic health and all-cause mortality: a systematic review and meta-analysis of prospective studies
Egg consumption in relation to risk of cardiovascular disease and diabetes: a systematic review and meta-analysis
Egg consumption and risk of incident type 2 diabetes: a dose-response meta-analysis of prospective cohort studies
Cholesterol, choline, and cancer
Eggs are rich in cholesterol and choline, each of which has cancer-promoting properties. Higher blood cholesterol and choline are both linked to increased risk of prostate cancer.11-13 Higher egg consumption (more than 5 eggs per week) is also linked to breast cancer, fatal prostate cancer, and gastrointestinal cancers, especially colon cancer.14,15
Cholesterol is enriched in tumor cells, and cholesterol influences cell proliferation and migration, processes that are vital to cancer development.16-18 Choline is also enriched in tumor cells, and has been implicated in colorectal cancers. Similar to carnitine from red meat, choline from eggs is metabolized by gut bacteria, and then the liver, into a pro-inflammatory compound called trimethyl-N-amine oxide (TMAO), and there is evidence TMAO contributes to chronic diseases, cancer included.19-22 A 2017 meta-analysis of 17 studies found that higher circulating TMAO levels were associated with a higher risk of cardiovascular and cerebrovascular events (such as heart attack and stroke) and all-cause mortality.23
A randomized controlled trial that tested multiple doses of egg yolks found that more egg yolk consumption led to greater TMAO production.24
Related: Animal products, the microbiome, and heart disease
Plus, egg whites are a highly concentrated source of animal protein, which carries its own risks by elevating circulating IGF-1, a hormone associated with cancer promotion.25-27
Related: Optimal IGF-1 Levels for Longevity
Sources:
Egg intake and cancers of the breast, ovary and prostate: a dose-response meta-analysis of prospective observational studies
Egg consumption and risk of GI neoplasms: dose-response meta-analysis and systematic review
The role of cholesterol metabolism and cholesterol transport in carcinogenesis: a review of scientific findings, relevant to future cancer therapeutics
Gut microbe-generated metabolite trimethylamine-N-oxide as cardiovascular risk biomarker: a systematic review and dose-response meta-analysis
Effect of egg ingestion on trimethylamine-N-oxide production in humans: a randomized, controlled, dose-response study
A Meta-analysis of Individual Participant Data Reveals an Association between Circulating Levels of IGF-I and Prostate Cancer Risk
Postprandial cholesterol and atherosclerosis
Dietary cholesterol intake has a relatively small effect on fasting blood cholesterol levels compared to saturated fat intake. However, the composition of each meal we eat influences the fats circulating in our blood in the hours following that meal. Fasting lipid levels measured first thing in the morning do not necessarily reflect the total exposure of our blood vessel walls to circulating lipids, such as cholesterol, all day long, considering we spend a large portion of the day in the postprandial (following a meal) state.
Several studies have shown that there is an increase in oxidative stress and/or a decrease in endothelial function in the hours following a high-animal fat meal.28 These factors promote the development of atherosclerotic plaque.29 Some researchers have proposed that postprandial effects of the high cholesterol content and gut microbiome metabolites (TMAO and others) of substances derived from eggs are significant contributors to atherosclerosis.22,30
Sources:
Cardiovascular Harm From Egg Yolk and Meat: More Than Just Cholesterol and Saturated Fat
A single high-fat meal adversely affects postprandial endothelial function: a systematic review and meta-analysis
Pollutants in eggs
Fatty animal foods are a major source of environmental contaminants known as persistent organic pollutants in the human diet. These pollutants are called “persistent” because they persist in the environment, and resist breaking down. These chemicals accumulate in fat tissue.31
Per- and polyfluoroalkyl substances (PFAS) are persistent organic pollutants. They are synthetic chemicals resistant to both water and oils that are used in products such as non-stick cookware, cleaning solutions, stain-resistant materials, and food packaging. PFAS are often called “forever chemicals” because of their resistance to breaking down. They are also endocrine disruptors, and are linked to immune system dysfunction, elevated cholesterol and triglyceride levels, cancer risk, and thyroid hormone disruption.32-35
Early in 2023, a study in Denmark found high levels of PFAS in both conventional and organic eggs. Previous studies detected other environmental pollutants with endocrine-disrupting activity, such as brominated flame retardants and PCBs in both conventional and organic Canadian eggs. Brominated flame retardants have also been detected in American eggs. Potential sources of these pollutants are fishmeal in chicken feed, or pollutants present in bedding materials.36-40
Sources:
Per- and polyfluoroalkyl substances (PFAS)-contaminants of emerging concern
Polybrominated diphenyl ether (PBDE) levels in an expanded market basket survey of U.S. food and estimated PBDE dietary intake by age and sex
Brominated flame retardants in Canadian chicken egg yolks
What to do
I do not recommend people eat eggs regularly. Even for healthy people, I advise caution, since some studies have suggested an increase in risk starting at only two eggs per week, and because of the potential exposure to pollutants. I recommend minimizing eggs, together with other animal products, to no more than 5% of your total calories. Instead, eat beans, greens, nuts and seeds, which are protein-adequate, with dramatic and proven health benefits.