Proteins are made up of amino acids. There are 20 amino acids (synthesized by genetic code), and 9 of them are essential.
Essential amino acids are amino acids that cannot be produced within the body, and that must be entered by eating various foods. Essential amino acids are methionine, valine, tryptophan, isoleucine, leucine, lysine, threonine, phenylalanine, and histidine.
