You’ve just enjoyed your annual Turkey Day dinner (if you’re honest, you probably enjoyed it a little too much), and now you’re sleepy, or even exhausted. But why? Tryptophan, one of the natural, essential 22 amino acids found in the human diet, has long been blamed as the scientific cause for that feeling of fatigue after a turkey dinner. But is it just a myth? Here are four fast facts about tryptophan and why eating turkey on Thanksgiving can make you tired:


Though tryptophan has a reputation for causing sleepy side effects, a study from Psychology Today claims that it acts only as a mood stabilizer. “Tryptophan achieves its effects by way of serotonin, one of the key brain chemicals involved in regulating mood,” states the report, adding, “Among other functions, serotonin promotes feelings of calm, relaxation and sleepiness.” Consuming tryptophan is so effective for treating mood disorders (such as depression) that it is even prescribed as a dietary supplement to some in other countries, such as Canada.


Despite the fact that turkey is high in tryptophan, its amino acid quantity doesn’t substantially differ from many other high-protein foods, including meat, fish and dairy products such as cheese and eggs. In fact, according to American Dietetic Association spokeswoman Dawn Jackson Blatner, RD, LDN, chicken actually contains more tryptophan than turkey.


Have an especially aggressive in-law visiting for Thanksgiving? Give him a big serving of turkey. When family gets together, especially during the holidays, it isn’t uncommon for a quarrel or two to break out. But consuming tryptophan has been known to significantly reduce aggression and irritability.


Despite the unusually high quantities of meat consumed on Thanksgiving, the large amount of carbohydrates-filled side dishes on Turkey Day can also contribute to the tired feeling many experience after enjoying their holiday meal. “When carbohydrates are consumed, the body produces insulin, which diverts other amino acids to body muscles but leaves tryptophan untouched,” explained a report from Psychology Today. “With fewer competitor amino acids in the bloodstream, tryptophan more freely enters the brain, promoting calm and well-being.”

Blatner gave another explanation via a Web MD report, saying, “It boils down to Thanksgiving being a time when people overeat. When people overeat food, the digestion process takes a lot of energy. Don't incriminate the turkey that you ate. Incriminate the three plates of food that you piled high," she said.