The intake of whole egg can contribute to the gain of muscle mass regardless of its protein content. An average egg weighs approximately 50g (33g egg white and 17g yolk), of which 12.5% of its mass corresponds to protein (mainly albumin). Albumin is a high-quality source of protein, requiring an intake of approximately 20 g to maximize protein synthesis in a single meal. The yolk comprises about 40% of the total protein in an egg, as well as containing several other non-protein nutrients with potential anabolic effects, such as microRNAs, vitamins, minerals, lipids, phosphatidic acid and other phospholipids, suggesting that whole eggs can be a food source with the potential to contribute to increasing muscle mass, regardless of their protein content.
One egg contains approximately 6g of lipids, of which 30% (1.8 g) are phospholipids. Of the total phospholipids, 72% is phosphatidylcholine, with the egg being an important source of this nutrient. Another phospholipid present in the egg is phosphatidic acid, which has been investigated for stimulating mTOR, protein synthesis and muscle mass. Another lipid present in the egg is omega - 3 fatty acid (about 0.002 g of EPA and 0.019 g of DHA), which increases the fluidity of the membrane of muscle fibers, improving the uptake of amino acids and, consequently, makes the cell more sensitive to protein synthesis. In addition, omega-3 has anti-inflammatory effects, which can result in positive effects on muscle mass, since increased inflammation is an established cause of muscle loss.
One egg also contains about 225 mg of cholesterol, which can have indirect anabolic effects, since testosterone is synthesized from cholesterol. However, its anabolic effect seems to be minimal to promote muscle hypertrophy. Egg yolk also contains vitamin D and, despite the low amount (1 egg contains only 37ui of vitamin D), can contribute to the endogenous pool of this important vitamin, which has been positively associated with muscle mass.
Whole egg intake appears to promote greater myofibrillar protein synthesis than egg white intake alone. However, limited evidence shows no difference in muscle hypertrophy when comparing whole egg consumption versus an isonitrogenated amount of egg white in young men performing resistance training. Although egg yolk intake appears to promote additional acute increases in myofibrillar protein synthesis, it does not appear to further increase muscle mass when compared to egg white when consumed as part of a protein-rich dietary pattern, at least in young men. This conclusion is based on very limited evidence and further studies are needed to assess the effects of egg yolk (or whole eggs) intake on muscle mass not only in young men, but also in other populations such as women, the elderly, and individuals with muscle wasting disease.
Consumption of 1 to 3 whole eggs per day increased total cholesterol by 5.6 mg/dl, LDL-c by 5.5 mg/dl, and HDL-c by 2.1 mg/dl. However, these increases in total cholesterol and LDL-c do not necessarily lead to cardiovascular events. Thus, the consumption of up to 3 eggs per day does not affect the risk of cardiovascular disease and mortality.