Phenylalanine is an amino acid, which are the building blocks of proteins in your body.
This molecule exists in two forms or arrangements: L-phenylalanine and D-phenylalanine. They’re nearly identical but have a slightly different molecular structure.
The L-form is found in foods and used to produce proteins in your body, while the D-form can be synthesized for use in certain medical applications.
Your body is unable to produce enough L-phenylalanine on its own, so it’s considered an essential amino acid that must be obtained through your diet.
It’s found in a wide variety of foods — both plant and animal sources.
Your body needs phenylalanine and other amino acids to make proteins.
Many important proteins are found in your brain, blood, muscles, internal organs and virtually everywhere else in your body.