Amino acids are vital, as they allow the human body to grow and function properly. Essential amino acids are amino acids that cannot be made by the body, and therefore must come from food/ your diet. There are 9 essential amino acids. These are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. The best source of essential amino acids are animal proteins like meat, eggs, and poultry.