Phenylketonurics: Phenylalanine

Phenylalanine is an essential amino acid, meaning the body needs it but cannot make it. It is one of the 20 amino acids that make up proteins. It can be found naturally in protein-rich foods like meat, fish, eggs, and dairy.

Phenylalanine is not typically added to foods as an ingredient. However, it is a component of the artificial sweetener aspartame (Equal, NutraSweet). When aspartame is digested, it breaks down into phenylalanine, aspartic acid, and methanol. Foods containing aspartame include diet sodas, sugar-free candies, and some yogurts.

The U.S. Food and Drug Administration (FDA) requires foods containing aspartame to carry a warning label for individuals with phenylketonuria (PKU). PKU is a rare genetic disorder where the body cannot properly metabolize phenylalanine, leading to its buildup to toxic levels. For people without PKU, phenylalanine from aspartame is generally considered safe. The Joint FAO/WHO Expert Committee on Food Additives (JECFA) has evaluated aspartame and established an acceptable daily intake (ADI).