Hi. It has been common knowledge that egg whites do contain protein, while the yolk contains a much smaller portion. My friend, who has taken an animal biology class, contends that we, the public, have been misled, and egg whites do not contain as much protein as proclaimed. Can this be true?
I used to eat a lot of eggs when I was a competitive bodybuilder. IIRC, the white of an average-sized egg contained 4 to 5 grams of protein. The yolks contain more, but also contain all the fat and cholesterol of the egg.
I recall that some claimed there was a substance called albumen (sic) present in the white that interfered with the absorption of protein. This effect was supposedly counteracted by cooking, for which reason it was advised not to eat eggs raw if you wanted the full dose of protein.
Perhaps this is what your friend was talking about?
Albumen is a type of protein found in egg whites.
According to On Food and Cooking (second edition) by Harold McGee, 90% of an egg white is water (by weight). Most of the rest is protein, with traces of minerals, vitamins and glucose. There are several different types of proteins in egg whites.
The problem with eating raw egg whites (again according to McGee) is that three of the proteins bind to vitamins, one binds to iron, and one blocks digestive enzymes. These proteins help protect the egg against predators and bacteria. Cooking denatures the proteins so they no longer have the same chemical effects. Eating large amounts of uncooked egg whites could cause vitamin and iron deficiencies.
People who eat egg whites raw on a continual basis develop a biotin deficiency quite quickly if the eggs whites are not cooked. Adenine, a protein in egg whites, blocks the absorption of biotin, which is denatured if heated, thereby posing no threat. Back to the original q, however, I am not thoroughly convinced that egg whites contain as much protein as claimed.
I’ve never heard this claim. I’ve heard from various sources that yolks and whites contain roughly equal amounts of protein, so if you want to eat only the whites, eat twice as many to get the same protein.
Again, from On Food and Cooking by Harold McGee, the white from a U.S. Large egg contains 3.9 grams of protein, while the yolk contains 2.7 grams of protein. So, the yolk contains about 69% as much protein as the white. I don’t know whether to consider this “much less” or “roughly equal.”