Why are you sleepy after a big Thanksgiving dinner?
Elisabetta Politi, nutrition director at the Duke Diet and Fitness Center, explains why so many Americans nod off after big helpings of turkey and dressing, cranberry sauce, pumpkin pie and....
Q: I have heard that the reason we are so sleepy after Thanksgiving dinner is all the tryptophan in the turkey. What is tryptophan?
Tryptophan is an amino acid, which are the building blocks of proteins. So when you eat a meal that contains protein, the proteins are broken down into amino acids. Several of these amino acids, like valine, leucine and isoleucine, are taken into the cells for energy, but not tryptophan. It stays in the bloodstream, eventually going to the brain, where it is converted into serotonin, this well-being chemical that has been shown to make you feel relaxed.
Q: So is turkey particularly high in tryptophan? Is that the real culprit?
No, because when we look at the content of tryptophan in turkey, it is comparable to chicken, beef and other meats. Tryptophan is also found in soybeans, sunflower seeds, sesame seeds, which are really not linked to causing sleepiness. So it is somehow a myth that when you have the Thanksgiving meal you are going to feel sleepy because of the turkey. I think people tend to feel sleepy after Thanksgiving more because of the size of the meal.
Q: Could you explain how the size of the meal could slow us down?
It is really two major shifts. The first involves the parasympathetic system - the opposite of the sympathetic system, also known as the fight or flight system - the one that makes us be really active and ready to fight. After a meal we switch to the parasympathetic system, which diverts the blood flow from all over the body to the stomach to help digest the food.
The second system involves changes in hormonal status. After a meal insulin increases, changing the amount of hormones in the blood, and as a result we tend to feel more tired. This is where you get more serotonin because more tryptophan is being converted. And the larger the meal, the more that system is activated.
Q: I understand that other aspects of the Thanksgiving meal - carbohydrates, desserts and alcohol - can also cause you to feel sleepy. To me, it seems counterintuitive that dessert would make you sleepy. Doesn't sugar make you hyperactive?
Well, when you have just pure sugar,it will make you hyperactive. But desserts like cookies and pies and cakes contain both sugar and fat, and fat blunts the blood sugar rise.
Q: What can people do to keep from getting so sleepy after that infamous meal?
I usually recommend two things. Eat more proteins and fewer carbohydrates, because I think it is usually the carbs that make people sleepy. And then stay active after eating - go for a walk, for instance.