for National Geographic News
Thanksgiving feasters take heart. Contrary to popular belief, turkey's tryptophan dose doesn't cause drowsiness. In fact, the substance could possibly aid in the treatment of depression and multiple sclerosis.
Purified tryptophan is a mild sleep-inducing agent. That probably spawned the idea that turkey and other foods heavy in tryptophan cause drowsiness.
But tryptophan can't get to the human brain in large amounts when ingested as part of a massive Thanksgiving feastit needs an empty stomach.
"Tryptophan is taken to the brain by an active transport system shared by a number of other amino acids [the chief components of proteins], and there's competition among themlike a crowd of people trying to get through a revolving door," said Simon Young, a neurochemist at McGill University in Montreal, Canada.
Consuming tryptophan-rich foods may cause blood levels of the amino acid to rise. But not enough tryptophan will reach the brain to have a sedative affect.
"Brain levels of tryptophan could even go down after a big meal because of the [amino acid] competition," Young said.
Turkey isn't even unusually high in tryptophan. Many foods, such as beef or soybeans, boast higher concentrations.
"Think about how much turkey you have in a turkey sandwich without getting tired," said Sherrie Rosenblatt, spokesperson for the National Turkey Federation. The Washington, D.C. nonprofit represents the turkey industry.
So why the traditional Thanksgiving nap?
The slumber may be caused by the stressful hustle and bustle of the holidays, alcohol consumption, and the massive caloric intake of the year's biggest feast.
"There have been many studies citing a post-lunch dip in performance, from factory output to single-car accidents," McGill's Young explained.
"These things tend to peak in the early afternoon. A thousand-calorie lunch causes a sedative effect that a smaller meal doesn't have."
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