It's Thanksgiving evening. The family just finished a huge meal of mashed potatoes, gravy, creamed onions, squash, sweet potatoes, Waldorf salad, a Jello mold, wine, cranberry sauce, green bean casserole, pumpkin pie, apple pie, and, of course, turkey. Or at least my family did. Now we're sitting in the living room, a fire crackles in the background, and I have one those moments when you fell asleep without realizing it. I look around and notice that half the family is asleep, and the other half appears to be in a drug-induced lethargy. As I shake off the last vestiges of sleep, I remember hearing that turkey has tryptophan in it, which causes " turkey coma".
Is there something special about turkey that causes sleepiness?
Tryptophan and Serotonin
Turkey contains tryptophan. Tryptophan does cause a sedative-like effect on the body, and it is also a chemical precursor of serotonin. Serotonin is one of a group of chemical messengers known as neurotransmitters that carry out communication in the brain and body. Low serotonin levels have been linked to sleep disorders and depression. When you consume tryptophan, your body can convert it into serotonin and hence raise serotonin levels. The synthesis of serotonin is a two-step process involving a hydroxylation reaction catalyzed by the enzyme tryptophan-5-monooxygenase and then a decarboxylation catalyzed by l-amino acid decarboxylase. Hence, tryptophan consumption can raise serotonin levels.
Several factors should diminish the special way we perceive the sleep-inducing ability of turkey. For one, turkey is not so special. Equivalent servings of chicken and ground beef contain equivalent amounts of tryptophan (about 320 mg per 3.5 oz). We don't normally associate sleepiness with these foods.
Also, for people who need tryptophan supplements, it is recommended that they take them on an empty stomach. This makes absorption much easier, and the tryptophan does not have to compete with other nutrients. The "Thanksgiving stomach" is not an ideal situation for absorption; tryptophan has to compete with other amino acids and all the food consumed, before it can be digested and then absorbed.
The Thanksgiving meal offers so may other reasons to be tired besides the turkey. Here are a few:
- The full stomach. A big, solid meal has been shown to induce sleepiness regardless of what you've eaten. In response to a full stomach, your body gears up for digestion. The body increases blood flow to the stomach, which results in decreased oxygenation and blood flow to the brain.
- Wine, wine, wine. A glass or two of wine, especially for people who only partake on occasion, is all that is needed to induce sleepiness.
- Long day. At least for the cook it is, what with getting up early to start the preparations. Although it doesn't have to be, it can be exhausting. Now that I've cooked my first Thanksgiving dinner, I'm surprised my mother never fell asleep in the mashed potatoes at dinner.
In the end, tryptophan and turkey probably play some role in the more general "Thanksgiving coma", but it is not the only one. I suspect substitution of a 10-lb Thanksgiving hamburger for your turkey will have the same result.
In any event, avoid operating heavy machinery, and enjoy your turkey!
This article originally appeared on November 19, 2001, and was republished on November 22, 2004.