When it comes to the myth that Thanksgiving dinner makes us sleepy, Judith Wurtman takes the side of the big roast bird.
Wurtman, a researcher affiliated with MIT's Clinical Research Center, is co-author of a new book on the interaction between nutrition and brain chemistry. And she warns those about to settle in at the groaning board: The turkey is not responsible for drowsiness after the meal.
While it is true that tryptophan--an amino acid present in all protein--does make serotonin, which makes us relaxed, tryptophan from turkey alone is not what makes us tired, said Wurtman, whose PhD is in nutritional biochemistry.
Instead, it is the combination of the high-fat, high-carbohydrate food we eat as sides to the turkey--the sweet potatoes and marshmallows with brown sugar, the mashed potatoes, stuffing, gravy and sugar-filled cranberry sauce--that contribute to the exhaustion many people experience.
As Wurtman explains it, amino acids are found in all proteins, from cottage cheese to eggs. Among the amino acids that make up a protein, trytophan is the most limited, she said. Wurtman likened the process of amino acids journeying into the brain to hundreds of people trying to get through a subway turnstile. "Tryptophan stands little chance of getting through under normal circumstances," Wurtman said.
Add all the carbohydrates the typical American consumes during dinner, though, and the story changes, Wurtman said. Carbohydrates release insulin, which acts like a broom in the blood, chasing all but the tryptophan away. "Tryptophan ends up there rather alone," she said. Hence, it has a better chance of getting into the brain than it would have under normal circumstances.
Additionally, the other meal accoutrements--cheese puffs before dinner, wine throughout--add to that sleepy feeling, Wurtman said.
As for the "suburban" aspect of the myth, Wurtman notes, the post-turkey tiredness falls unequally on men and women.
"Who is in the living room munching on nuts and watching the ball game?" Wurtman asks with a laugh.
Joking aside, Thanksgiving does a powerful thing in our obese culture, Wurtman said, recalling a bulimic woman she once knew who called the holiday "national eating disorder day."
"We all give ourselves permission to eat without control," Wurtman said. As someone who spends a lot of her work trying to help people lose weight, she is amazed by the holiday, which "does for supermarkets what Christmas does for retailers. It is all about excess. The whole thing is just a way of guilting people to shop."
For Wurtman's own Thanksgiving meal, health is the key. "It is not necessary to have excessive amounts of food," she said. Wurtman said she uses the opportunity to make different kinds of root vegetables--parsnips and turnips, for example --but that she does not drown them in butter. "To me, being healthy is important."
Wurtman's new book, "The Serotonin Power Diet: Use Your Brain's Natural Chemistry to Cut Cravings, Curb Emotional Overeating and Lose Weight," will be published December 12.
A version of this article appeared in MIT Tech Talk on November 22, 2006 (download PDF).
