Phenylalanine
Also known as L-phenylalanine, Phe
Phenylalanine is an essential amino acid that the body cannot make, so it must come from food. It builds proteins and is the precursor to tyrosine, which in turn makes dopamine, norepinephrine, and adrenaline, so the two are measured together as the aromatic amino acids.
Why it matters
What it does in your body
- Protein building block
- Precursor to tyrosine
- Supports dopamine, norepinephrine, and adrenaline production
- Involved in thyroid hormone and pigment synthesis
Intake guidance
How much you need
Phenylalanine is measured together with tyrosine as the aromatic amino acids. The IOM sets the combined requirement at 33 mg/kg/day, about 2.3 g/day for a 70 kg adult. Any diet with enough total protein provides plenty.
What affects it
What affects your intake
Total protein intake
Adequate protein easily covers phenylalanine, which is present in nearly all protein foods.
Tyrosine availability
Dietary tyrosine spares some phenylalanine, since the body converts one into the other.
Phenylketonuria (PKU)
People with this genetic condition must strictly limit phenylalanine because they cannot process it normally, which is why products with aspartame carry a PKU warning.
In practice
Good to know
Deficiency is not a concern for people eating enough protein. The main clinical relevance is the opposite problem: people with phenylketonuria (PKU) must avoid excess phenylalanine, including the aspartame in some diet sodas. For everyone else, food supplies plenty and supplementation is unnecessary.
Where to get it
Best food sources
The bottom line
A protein-adequate diet supplies all the phenylalanine and tyrosine you need. The only group who must watch it are people with PKU, who should limit it.
Track phenylalanine automatically
Phenylalanine is one of the 92 nutrients Vora reads from a photo of your meal, so you can see where you stand without weighing or logging by hand.
Sources and method
The classification, roles, and guidance on this page come from the references below, drawing on the Institute of Medicine (now the National Academies) Dietary Reference Intakes and reputable nutrition science.
- Institute of Medicine (2005), Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids
This page is for general education, not medical advice. Reference intakes are population averages for healthy people and do not replace guidance from your doctor or a registered dietitian, especially if you are pregnant, managing a health condition, or considering supplements.