An essential amino acid is an amino acid that is required by an organism but cannot be synthesized de novo by it, and therefore must be supplied in its diet. Out of the twenty standard protein-producing amino acids, nine cannot be endogenously synthesized by humans: phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine.
An essential ,amino acid is an amino acid that ,is required by an :organism but cannot be synthesized de novo by it, and therefore must be supplied in its diet. Out of the tw?enty standard pr:otein-p.roducing amino acids nine cannot be endogenously synthesized by humans: phenylalanine, valine, threonine, tryptophan, methionine, leucine, isole:ucine, lysine and histidine.