It is also needed for the body to produce enzymes, hormones, and antibodies that regulate body functions. The body needs the 20 different amino acids that act as building blocks to manufacture new protein. Some of the amino acids can be made in the body, but eight can only be supplied by the foods you eat. These eight are called essential amino acids. They are tryptophan, methionine, threonine, isoleucine, valine, lysine, leucine, and phenylalanine.
Infants also require histidine, a ninth essential amino acid.
They are all found in animal foods, which are referred to as high quality or complete proteins. Plant proteins are referred to as incomplete because they do not contain all eight of the essential amino acids. Essential amino acids can come either from animal foods or plant foods. Animal foods will provide the essential amino acids all at one time. Plant foods can provide the necessary amounts of amino acids when a variety of foods are eaten on a daily basis.