I found this article from LIVESTRONG.com. It helped clear up some confusion about the nutritional value of egg yolks versus egg whites.
Eggs are often referred to as super-foods, and with good reason. They provide an inexpensive source of protein and other nutrients. Separately, the yolk and white of an egg each have their own benefits.
White & Yolk Combined
Though some recipes call for eggs that have had their yolks and whites separated, most dishes contain the entire egg. Nutritionally, a whole, raw, fresh egg has more nutrients than either of its individual components. However, you also get the “bad” with the “good” when using both yolk and whites.
The yellow yolks of eggs are the real powerhouse of nutrition. The yolk contains all of the nutrients listed by the American Egg Board using the USDA’s National Nutrient Database for Standard Reference and by the Egg Nutrition Center. Those nutrients range from vitamins A, D, E, several B vitamins and choline to minerals such as calcium, sodium, potassium, phosphorus, magnesium, iron, zinc and selenium. Additionally, egg yolks are high in protein and carbohydrates, making them an ideal food for energy needs. Carotenoids lutein and zeaxanthin, which help maintain eye health, are found only in the egg yolk.
The yolk of an egg contains more than half of the entire egg’s calories and all of the fats, including the beneficial — monounsaturated and polyunsaturated — and harmful types — saturated and trans fats, according to the Mayo Clinic. Also, all of the cholesterol in an egg is in the yolk.
When word spread about cholesterol in egg yolks, a flurry of recipes using only egg whites were promoted, in addition to egg-substitute products. Egg whites do contain most of an egg’s protein, as well as fewer calories and none of the fat of egg yolk. Whites are also higher in potassium and magnesium than yolks.
Egg White Disadvantages
Of all of the vitamins in an egg, only B12, folate and riboflavin are in the egg white. They are also considerably higher in sodium, according to USDA charts available online. Egg whites contain no lutein or zeaxanthin.
Nutritionally Enhanced Eggs
Eggs from chickens that are fed special diets have additional nutrients, such as omega-3 fatty acids and increased amounts of some nutrients like vitamin E and lutein, according to the Egg Nutrition Center.
Crunching the Numbers
The white of a large egg, or about 1-1/4 ounces, has 16 calories, 3 g of protein, 2 mg of calcium, 4 mg of phosphorus, 55 mg of sodium, 45 mg of potassium, the weensiest little bit of riboflavin, and no fat, cholesterol, or carbohydrates.
The yolk of that egg weighs about 2/3 of an ounce, and has 59 calories, 3 g of protein, 5 g of fat (2 of which are saturated), 212 mg of cholesterol, 23 mg of calcium, 81 mg of phosphorus, 7 mg of sodium, 16 mg of potassium, very small amounts of iron, thiamin, and riboflavin, and no carbohydrates