Of the 20 amino acids your body needs to build proteins required for normal growth and maintenance of health, 9 are called essential amino acids, because they cannot be made by your body and must come from your diet, according to MedlinePlus.com. The 9 essential amino acids, found in isolated soy protein and many animal foods, are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. Arginine is essential for children but not adults. There are also 10 nonessential amino acids, found in various foods and in different combinations with some or all of the essential amino acids. Your body can make these nonessential amino acids if they are not provided by your diet.