Protein is essential for supplying the body with amino acids and is an important component of muscles, hair, nails and skin. But not all proteins are created equal. Soy protein is known as a complete protein, meaning it contains all the essential amino acids. It is also known to contain very little fat, cholesterol or lactose. For vegetarians and those with lactose intolerance, this type of protein is a good alternative to getting a non-animal protein in the diet. In addition to the usual benefits of a good protein, soy proteins include saponins, phytosterols and isoflavones. These various ingredients have been shown to have a number of positive health effects, from lowering cholesterol levels to improving the immune system.