Phenylalanine
Phenylalanine is an essential amino acid and the precursor to tyrosine, dopamine, norepinephrine, and epinephrine. It is also the carrier of the sweetener aspartame, which is why diet soda labels carry a warning for people with PKU.
Why It Matters
Phenylalanine sits at the top of the catecholamine production chain. Your body converts it to tyrosine, then to dopamine and adrenaline. That is why adequate phenylalanine intake matters for focus, drive, and the body's stress response, particularly under heavy training loads.
For people with phenylketonuria (PKU), phenylalanine must be strictly limited; all aspartame-sweetened products carry a label warning. For everyone else, phenylalanine in protein powders is harmless and beneficial.
How to Spot It on a Label
Look for L-phenylalanine on amino panels and the words contains phenylalanine or PHENYLKETONURICS: CONTAINS PHENYLALANINE on any product sweetened with aspartame. Most protein powders today use sucralose or stevia and do not carry this warning.
Examples from real products
Related Terms
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