L-Tryptophan is necessary for normal growth in infants and for nitrogen balance in adults, which cannot be synthesized from more basic substances in humans and other animals, suggesting that it is obtained only by intake of tryptophan or tryptophan-containing proteins for human body, which is particularly plentiful in chocolate, oats, milk, cottage cheese, red meat, eggs, fish, poultry, sesame, almonds, buckwheat, spirulina, and peanuts, etc. It can be used as a nutritional supplement for use as an antidepressant, anxiolytic, and sleep aid.