While not everyone stoops to the level of Seinfeld’s Jerry and George, who used the tryptophan in turkey to send a girl to sleep so that they could play with her toys, the supposed sleep-inducing effects of tryptophan in turkey are common currency in America, repeatedly recounted at Thanksgiving dinners and in the popular media around the holidays.
Turkey does contain tryptophan, an essential amino acid. And scientific evidence does support a connection between tryptophan and sleep. L-tryptophan has been marketed as a dietary supplement to ease insomnia. Tryptophan also may have an effect on the immune system, with possible benefits for autoimmune disorders such as multiple sclerosis.
But the truth is turkey is not the cause of your sleepiness. Chicken and minced beef contain almost the same amount of tryptophan as turkey – about 350 milligrams per 100 gram serving. While you might have heard someone claim that turkey made them drowsy, you have probably never heard anyone say that chicken, minced beef or any other meat made them sleepy. Swiss cheese and pork actually contain more tryptophan per gram than turkey, and yet that American classic, a ham and cheese sandwich, somehow escapes blame.
The amount of tryptophan in a single serving of turkey (350 milligrams) is also lower than the amount typically used to induce sleep. The tryptophan supplements to help you sleep contain 500 to 1,000 milligrams. Many scientists also think the limited amount of tryptophan in turkey would be offset by the fact that it is generally eaten in combination with other foods and not on an empty stomach. One clinical trial found comparable results for tryptophan from a food-protein source and pharmaceutical-grade tryptophan, but this study used an extremely rich source of tryptophan, deoiled gourd seeds, which have twice the tryptophan content of turkey. And in this trial, as in the general use of supplements, tryptophan was taken on an empty stomach to aid absorption. Although we did not locate any experimental evidence to support this claim, many believe that the presence of other proteins and food in the stomach during the feasts generally associated with turkey consumption would limit the absorption of the tryptophan in the turkey.
There are other elements of Christmas and Thanksgiving dinners that can induce drowsiness. Large meals have been shown to cause sleepiness regardless of what is eaten, because the body increases blood flow to the stomach and decreases blood flow to and oxygenation in the brain. Meals that are high in proteins or in carbohydrates may particularly cause drowsiness. And don’t forget about the booze. One or two glasses of wine, especially for people who only drink alcohol occasionally, can increase drowsiness.