The nutritional value of egg yolks: 1. they provide the body with vitamins, such as vitamin A and vitamin D, which are the raw materials for many enzymes and coenzymes in the body and are very important for regulating the body’s metabolism. 2. they provide the body with minerals, such as iron and zinc, which are also very important for regulating the body’s metabolism. 3. they provide the body with cholesterol, which is the raw material for cell membranes and many hormones. Cholesterol constitutes the raw material for cell membranes and many hormones, which in turn allows the body’s metabolism to proceed more smoothly.