Egg Yolks
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.
Yolk Disadvantages
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.
Egg Whites
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.
Read more: http://www.livestrong.com/article/273210-nutritional-value-egg-yolk-white/#ixzz1yAcMZwT0