EDIT: If you want to go all crazy-health-nut, the whites are 100% protein calories (~50/50 fat/protein in the yolks), have no cholesterol, and taste pretty much the same.
EDIT again: But I guess you don't really have much else in the way of fat sources, cheese aside. If you do this long-term, you might want to make sure your blood cholesterol levels don't go nuts.