Phenylalanine

High dietary protein intake may elevate phenylalanine levels. Additionally, some artificial sweeteners contain phenylalanine (NutraSweet and Equal); use of these products can result in higher levels. 

Phenylketonuria (PKU) is a rare genetic mutation of the phenylalanine hydroxylase enzyme which results in high phenylalanine levels. 

The enzyme requires vitamin C, tetrahydrobiopterin, and iron as cofactors. The mainstay of treatment involves a low-protein diet, cofactor support, and the use of a phenylalanine-free formulas.

Low levels of essential amino acids may indicate a poor-quality diet, or maldigestion due to deficient digestive peptidase activity or pancreatic dysfunction. 

Also, vitamin B3 deficiency has been associated with low levels of several amino acids.

Phenylalanine is an essential amino acid found in most foods which contain protein such as meat, fish, lentils, vegetables, and dairy. 

Phenylalanine is the precursor to another amino acid, tyrosine. Because tyrosine is needed to form several neurotransmitters (dopamine, epinephrine, and norepinephrine), as well as thyroid hormone and melanin, phenylalanine intake is important.