But nutritionists and other experts say that the tryptophan in turkey probably won't trigger the body to produce more serotonin because tryptophan works best on an empty stomach. The tryptophan in a Thanksgiving turkey has to vie with all the other amino acids that the body is trying to use. So only part of the tryptophan makes it to the brain to help produce serotonin.

It is the whole traditional Thanksgiving meal that can produce that after-dinner lethargy. The meal is quite often heavy and high in carbohydrates -- from mashed potatoes, bread, stuffing and pie -- and your body is working hard to digest that food. Also, if you drink alcohol with your dinner, you will likely feel its sedative effect, too.

There is a way to take advantage of the tryptophan in turkey. If you have trouble getting to sleep one night while there is still leftover turkey in the refrigerator, you could have a late snack of turkey and that, nutritionists say, might be the right amount of tryptophan on an empty stomach to help produce some serotonin.