Why Does Turkey Make You Sleepy? Blame Tryptophan

Does turkey dinner make you drowsy? Many people think eating turkey on Thanksgiving makes them sleepy. But, it turns out there is no magic ingredient in turkey itself that is causing people to feel sleepy. In fact, tryptophan -- the molecule blamed for making people feel drowsy after turkey dinner can be found in any meat source. The amount that gets consumed does matter though. People tend to overeat on Thanksgiving, and because the central element of any Thanksgiving feast, is in fact turkey, the consequence of eating too much of it is the tryptophan overdose. When ingested, tryptophan is converted to serotonin, the "hormone of happiness," implicated in making people feel good. But, serotonin does not only make us happy, it also makes us calm and relaxed.

Another theory revolving around turkey dinner sleepiness is that people tend to consume a lot of carbohydrates along with turkey on Thanksgiving, which can increase insulin levels. Through complex metabolic processes, the ratios of amino acids in the blood change, resulting in induced uptake of tryptophan into the blood system. The 2002 study in the Journal of Psychiatric Research finally put an end to all doubts. It found that high doses of tryptophan increase sleepiness and decrease the time it takes to fall asleep.

Tryptophan is so effective in inducing sleepiness, that it is sometimes used as a sleep aid to fight insomnia. It has also been used to treat mood disorders, such as seasonal affective disorder. Maybe that is why North Americans celebrate Thanksgiving in the fall, when it is dark and miserable outside -- loading up on turkey just might do the trick of getting you back in the mood before Christmas shopping kicks off tomorrow morning. For the meaning behind Black Friday, see previous NowPublic coverage here.