Phenylalanine

Phenylalanine is an essential amino acid. The human body cannot make it so it is essential to the diet. Phenylalanine that is ingested is largely transformed (hydroxylated) to form the amino acid tyrosine, which is used in protein synthesis. Too little phenylalanine can curb physical and intellectual growth. And, too much phenylalanine can be highly toxic to the brain (phenylketonuria (PKU)).

Phenylalanine occurs in significant amounts in milk, eggs and other common foods.