A 50-gram (1.8 oz) medium/large chicken egg provides approximately 70 kilocalories (290 kJ) of food energy and 6 grams of protein. Eggs (boiled) supply several vitamins and minerals as significant amounts of the Daily Value. The diet of laying hens also may affect the nutritional quality of eggs. For instance, chicken eggs that are especially high in omega-3 fatty acids are produced by feeding hens a diet containing polyunsaturated fats from sources such as fish oil, chia seeds, or flaxseeds. Pasture-raised free-range hens, which forage for their own food, also produce eggs that are relatively enriched in omega-3 fatty acids when compared to those of cage-raised chickens.
More than half the calories found in eggs come from the fat in the yolk; 50 grams of chicken egg (the contents of an egg just large enough to be classified as "large" in the US, but "medium" in Europe) contains approximately five grams of fat. Saturated fat (palmitic, stearic, and myristic acids) makes up 27 percent of the fat in egg. The egg white consists primarily of water (around 90 percent) and protein (around 10 percent) and contains no cholesterol and little, if any, fat.
There is debate over whether egg yolk presents a health risk. Some research suggests dietary cholesterol increases the ratio of total to HDL cholesterol and, therefore, adversely affects the body's cholesterol profile; whereas other studies show that moderate consumption of eggs, up to one a day, does not appear to increase heart disease risk in healthy individuals. Harold McGee argues that the cholesterol in the egg yolk is not what causes a problem, because fat (particularly saturated fat) is much more likely to raise cholesterol levels than the consumption of cholesterol.
Studies have shown conflicting results about a possible connection between egg consumption and type 2 diabetes.
A meta-analysis from 2013 found that eating four eggs per week was associated with a 29 percent increase in the relative risk of developing diabetes. Another meta-analysis from 2013 also supported the idea that egg consumption may lead to an increased incidence of type two diabetes. A 2016 meta-analysis suggested that association of egg consumption with increased risk of incident type 2 diabetes may be restricted to cohort studies from the United States.
A 2020 meta-analysis found that there was no overall association between moderate egg consumption and risk of type 2 diabetes and that the risk found in US studies was not found in European or Asian studies.
A 2015 meta-analysis found an association between higher egg consumption (5 a week) with increased risk of breast cancer compared to no egg consumption. Another meta-analysis found that egg consumption may increase ovarian cancer risk.
A 2019 meta-analysis found an association between high egg consumption and risk of upper aero-digestive tract cancers in hospital-based case-control studies.
A 2021 review did not find a significant association between egg consumption and breast cancer.[66] A 2021 umbrella review found that egg consumption significantly increases the risk of ovarian cancer.