Turkey, tryptophan, and a Thanksgiving myth
Thanksgiving day is coming and along with it comes a popular myth that gets repeated without question. The tryptophan in turkey causes the drowsiness that one feels after a big thanksgiving meal. It seems to be ingrained in our culture. Even Jerry Seinfeld used turkey in an episode of his hit comedy series to trick his girlfriend into falling asleep. We have all heard this myth and probably repeated it to others, but how much truth is there really to this claim?
There is a small inkling of truth behind tryptophan leading to drowsiness, but it is indirect at best. Tryptophan is used by the brain to produce the compound melatonin, which is a sleep inducing hormone released at night. However, tryptophan is not limited to this function and is used as a precursor for serotonin, a precursor for niacin, and is a key amino acid found in every protein. More importantly, tryptophan has not been shown to be an effective sleep aid in well-controlled studies. Therefore, its direct action as a depressant is questionable.
More importantly, is turkey even really high in tryptophan? Wikipedia has a nice table of the content of tryptophan in various foods. Turkey is not especially high in overall levels or even in concentration of tryptophan. Chicken and beef contain about the same levels of tryptophan. If the culprit making you tired after eating turkey is tryptophan, then why wouldn’t you be just as tired from eating those meats?
So why do people feel sleepy after a large Thanksgiving meal? Undoubtedly a large part is simply due to the vast amounts of food consumed. It is also thought that eating large amounts of carbohydrates leads to increases in insulin, indirectly leading to increased transport of tryptophan into the brain. Couple that with a period of excitement followed by a period of relaxation at the dinner table, perhaps a little alcohol consumption, and you have a recipe for drowsiness.
So enjoy your turkey with a little healthy dose of skepticism!