Once the general public accepts that dietary cholesterol is not a concern for cardiovascular disease risk, foods that have been labeled as high-cholesterol sources, including eggs, may be appreciated for their various other dietary components. One of the nutrients in eggs that deserves further discussion is egg protein. Egg protein has been recognized to be highly digestible and an excellent source of essential amino acids, with the highest attainable protein digestibility-corrected amino acid score. Egg protein has been shown to decrease malnutrition in underdeveloped countries, possibly increase height in children, and protect against kwashiorkor. Egg protein has been demonstrated to be important to skeletal muscle health and protective against sarcopenia. Egg protein can also decrease appetite, resulting in a reduction in caloric intake from the next meal and weight reduction. Other protective effects of egg protein addressed in this review include protection against infection as well as hypotensive and anti-cancer effects. Eggs are a controversial food item due to their relatively high content of dietary cholesterol. The 2015 United States Department of Agriculture (USDA) Dietary Guidelines for Americans removed the upper limit for dietary cholesterol, emphasizing that eggs no longer need to be restricted. Furthermore, numerous studies conducted in both healthy and non-healthy populations have clearly indicated that eggs do not increase biomarkers associated with heart disease risk. In contrast, eggs contain several nutritional components that protect against chronic disease, including lutein, zeaxanthin, choline, vitamin D, selenium, and vitamin A. An additional beneficial nutrient present in eggs is protein. It is well established that eggs are one of the best dietary sources of high-quality protein, with all of the essential amino acids, and are recognized for their high biological value. In fact, eggs are considered to be the perfect protein source, serving as the standard for comparison for other protein sources. According to the 2018 USDA National Nutrient Database, one large egg contains 6.3 g of protein distributed between the yolk and white portions (3.6 g in egg white and 2.7 g in egg yolk).
The composition and function of protein in egg whites and egg yolk vary and are associated with biological and antimicrobial activities. For example, in egg whites, ovotransferrin binds metal ions, ovomucin has antiviral properties, and lysozyme disrupts the cell walls of Gram-positive bacteria. Similarly, egg yolk contains lipovitellin, representing the HDL subfraction in the egg yolk, and phosvitin, which protects against lipid oxidation by binding heavy metal ions. One thing that needs to be taken into consideration regarding eggs is the presence of egg allergies that have been identified in children, which are due mostly to the proteins present in the egg whites.
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