Tyrosine and tryptophan are two of the 20 amino acids, molecules that are arranged in chains to make up protein. The human body requires both to synthesize protein, an important component of multiple metabolic functions, but while tyrosine can be both manufactured naturally by the body and obtained through the diet, tryptophan can only be consumed in foods. Foods that supply both tyrosine and tryptophan include meats like chicken and turkey, fish, milk, cheese, soybeans, and pumpkin and sesame seeds.
The protein found in food, as well as that the body can produce on its own, are made up of smaller units known as amino acids, which are arranged in chains. Of these, eight are considered essential amino acids, meaning that the body cannot manufacture them and therefore they must come from foods in the diet. Tryptophan is an essential amino acid, one that is needed by the body to synthesize serotonin and niacin, as well as other chemical compounds.
By contrast, the remaining 12 nonessential amino acids are those that the human body can synthesize. Tyrosine is often grouped here, although it is sometimes referred to as a conditionally essential amino acid, meaning that in certain circumstances it may be advisable to get it through food or in supplement form. For example, those prone to depression may benefit from supplementing with tyrosine during times of elevated stress, as tyrosine is known to elevate levels of dopamine and norepinephrine, also known as noradrenaline, a stress hormone.
Both tyrosine and tryptophan, then, are amino acids that act as chemical precursors to hormonal neurotransmitters like dopamine and serotonin. A precursor is a substance that is necessary to manufacture a different chemical substance. In other words, these amino acids are used in the chemical reactions that create certain neurotransmitters in the body, chemicals that deliver electrical signals along neurons between the central nervous system and the body.
It is often recommended that individuals consume foods rich in both tryptophan and tyrosine to ensure they meet their need for both amino acids. Since many animals that humans eat can synthesize both amino acids, consuming meat or other animal products can supply tyrosine and tryptophan. Poultry, like turkey and chicken, is rich in both, as are fish like salmon and cod. Milk, cheese, and other dairy products also provide these amino acids. Several plant foods naturally contain tyrosine and tryptophan as well. Among those that contain both are sesame seeds, pumpkin seeds, soybeans, and other soy products.