An egg is really three separate foods, the whole egg, the white,
and the yolk, each with its own distinct nutritional profile.
A whole egg is a high-fat, high-cholesterol, high-quality
protein food packaged in a high-calcium shell that can be grounded
and added to any recipe. The proteins in eggs, with sufficient
amounts of all the essential amino acids, are 99 percent
digestible, the standard by which all other proteins are
judged.
The egg white is a high-protein, low-fat food with virtually no
cholesterol. Its only important vitamin is riboflavin (vitamin B2),
a visible vitamin that gives egg white a slightly greenish cast.
Raw egg whites contain avidin, an antinutrient that binds biotin a
B complex vitamin formerly known as vitamin H, into an insoluble
compound. Cooking the egg inactivates avidin.
An egg yolk is a high-fat, high-cholesterol, high-protein food,
a good source of vitamin A derived from carotenes eaten by the
laying hen, plus vitamin D, B vitamins, and heme iron, the form of
iron most easily absorbed by your body.
One large egg has 5 g Eat (1.5 g saturated fat), 212 mg
cholesterol, 6 g protein, 950 IU vitamin A (19 percent of the RDA
for a man, 23.7 percent of the RDA for a woman), and 0.72 mg iron
(4.8 percent of the RDA for a woman of childbearing age).
One large egg white has 4 g protein, but no Eat or cholesterol.
One large egg yolk has 6 g fat (1.7 g saturated fat), 272 mg
cholesterol, 3 g protein, and 970 IU vitamin A (19.4 percent of the
RDA for a man, 24 percent of the RDA for a woman).
The most nutritious way to server egg is with extra whites and
fewer yolks to lower the fat and cholesterol per serving. Those on
controlled-fat, low-cholesterol diet or low-protein diet should
exclude this food.