There are 20 amino acids found in the human protein, only 11 can be synthesize by the body and 9 must be supplied by the foods we eat which are also called as essential amino acids. Adults only need to obtain 8 of them which are valine, isoleucine, leucine, lysine, methionine, phenylalamine, threonine and tryptophan. The 9th amino acid- histidine - is essential for infants.