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Phenylalanine is an essential amino acid found in 3 forms:

  • L-phenylalanine, the natural form found in proteins
  • D-phenylalanine, a synthetic form
  • DL-phenylalanine, a combination of the other two forms

The body changes phenylalanine into tyrosine another amino acid that's needed to make proteins, brain chemicals, including L-dopa, epinephrine, and norepinephrine, and thyroid hormones

L-phenylalanine is found in most foods that contain protein such as beef, poultry, pork, fish, milk, yogurt, eggs, cheese, soy products and certain nuts and seeds.

The artificial sweetener aspartame is also high in phenylalanine.

Phenylalanine can be taken as a capsule, powder, or tablet. It can also be used as a topical cream.

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