Thanksgiving is around the corner in Canada and the USA. Around the office and among friends, someone will undoubtedly comment that they were sleepy after their turkey dinner, and then someone else will pipe up and say, “That’s because turkey contains tryptophan, which makes you sleepy.”

While it is true that turkey does contain tryptophan and tryptophan does make humans sleepy, it’s not necessarily true that “eating turkey makes you sleepy”. Here’s why:

L-tryptophan is an essential amino acid with a scientifically recognized sleep inducing effect. It is used in the body to produce niacin, a B Vitamin. Tryptophan can be metabolized into serotonin and melatonin, which are neurotransmitters that cause a calming effect and help to regulate sleep. But here’s the kicker: L-tryptophan needs to be taken on an empty stomach and without any other amino acids or protein in order to make you drowsy. In other words, the act of eating turkey (a source of protein) negates the sleep-inducing effects of tryptophan.

thanksgiving turkey, sleepy, tryptophanTIt’s also worth noting that several other foods contain as much or more tryptophan than turkey including chicken, pork, and cheese. As with turkey, other amino acids are present in these foods besides tryptophan, so they negate the sleepiness effect. Tryptophan also occurs naturally in red meat, other dairy products, nuts, seeds, bananas, soy products, tuna, and shellfish. So turkey is nothing special when it comes to its concentration of tryptophan – you can get a similar dose by eating shrimp, tuna, snapper, and even chicken breast. Oddly enough, people don’t react the same way after eating those items, do they?

So why do we feel sleepy after eating our turkey dinner, if it’s not the tryptophan?

Consider this: you’re on vacation, and you’re already feeling pretty relaxed. You just ate a massive meal and probably ate too much. You probably had high levels of carbohydrates and fats with your meal, and you probably had a drink or two (or three… or four…).

Digestion of large meals (overeating) causes blood to be directed away from your organs and nervous system to your digestive system, which induces sleepiness. A meal that contains a lot of fat will cause the same effect. The less blood you have circulating around the rest of your body, the more sleepy you will become. Alcohol is a depressant and will, for a large part of the population, make you drowsy. All these things combine to make you sleepy and lethargic after your Thanksgiving feast!