While choosing straight-up egg whites does lower the omelet's calorie, fat, and cholesterol content, it also makes the meal void of vitamins B2, B12, D, and iron. If you're concerned about getting enough of those nutrients, a good option would be to eat an omelet made of one whole egg and two egg whites. It's still low in calories, fat, and cholesterol, but you'll get some vitamins from the egg yolk.
