As an essential amino acid, phenylalanine is necessary for the production of tyrosine in human body, which cannot be synthesized from more basic substances in humans and other animals, meaning that it is obtained only by ingestion of phenylalanine or phenylalanine- containing proteins, which is particularly rich in eggs, chicken, liver, beef, breast milk of mammals, and soybeans, etc. There are three forms of phenylalanine: L-phenylalanine, the natural form found in protein-rich foods, D-phenylalanine, the synthetic mirror image and DL-Phenylalanine (DLPA), the mixture of both forms made in the laboratory that can maximize benefits. DLPA is manufactured for medical, feed, and nutritional applications, which can be used to produce food and drink products. It is marketed as a nutritional supplement due to its reputed analgesic and antidepressant effects. Besides, it can be applied for depression, attention deficit-hyperactivity disorder (ADHD), Parkinson's disease, chronic pain, osteoarthritis, rheumatoid arthritis, alcohol withdrawal symptoms, and a skin disease called vitiligo.
