A medium-sized egg typically contains about 66 calories, 4.6 grams of fat, 6.4 grams of protein, 0.2 grams of salt and negligible amounts of carbohydrates. They are also a source of several vitamins, primarily vitamin B12 but also vitamin A, vitamin D, riboflavin, folate, biotin, choline and pantothenic acid. The minerals phosphorus, iodine and selenium are also present in eggs.
Eggs, especially the egg white, are a good source of protein by weight, which provides energy and nutrients to repair or grow new cells in the body. Vitamin B12 supports metabolism and the maintenance of red blood cells as well as the capabilities of the immune system and nerves. Phosphorus supports bones and teeth, and both selenium and biotin protect and aid hair. Vitamin A provides continued good eyesight and, along with biotin, helps to keep skin healthy.
Eggs contain cholesterol, which means those struggling to balance their cholesterol and individuals with diabetes should limit their intake. Eating eggs in moderation can, however, have a net positive effect on heart health due to their proteins, vitamins and minerals, as long as the consumption is less than one egg per day. Eating only egg whites without the yolks also helps with cholesterol intake.