Tryptophan is an α-amino acid (and essential) that is used in the biosynthesis of proteins. It serves several important purposes in the body, like nitrogen balance in adults and growth in infants. It also creates niacin, which is essential in creating the neurotransmitter serotonin. Tryptophan can be found in some foods, especially those high in protein. Foods known to be high in tryptophan include chicken, eggs, cheese, fish, peanuts, pumpkin and sesame seeds, milk, turkey, tofu and soy, chocolate. In order for tryptophan to be converted into niacin, however, the body needs to have enough iron, vitamin B-6, and vitamin B-2 (see: Wikipedia).