For as long as I can remember, turkey has been taking the rap as the cause of post-feast fatigue. Tryptophan, an amino acid in the turkey, has always been fingered as the culprit.
It is true that the human body uses tryptophan to produce a chemical in the brain called serotonin that helps regulate sleep. So this would lead one to deduce that more turkey = more tryptophan = more serotonin — right?
Wrong! According to Nutritionist Elizabeth Somer, when you eat a lot of protein, you "flood the blood with both tryptophan and its competing amino acids, all fighting for entry into the brain. That means only a small amount of tryptophan gets through — and serotonin levels don’t rise."
In other words, stop blaming the bird.
So why are we so sleepy after our holiday meals?
Neuropharmacologist Richard Wurtman of the Massachusetts Institute of Technology believes "what probably makes people sleepy after Thanksgiving dinner is dessert." The likely culprit? Carbs. "Eating carbohydrates increases brain serotonin in spite of the fact that there is no tryptophan in carbohydrates," Wurtman says.
Another possible source of drowsiness is simple over-indulgence. H. Craig Heller, a biologist at Stanford University in Palo Alto, California, remarks, "studies have indicated that stretching of the small intestine induces sleepiness and a protein–fat loading of the stomach induces sleepiness."
In simple terms, a big meal makes you sleepy. So this holiday season, relax. Enjoy dining with friends and family, treat yourself to a nap, and never fear tucking turkey leftovers into your workday lunch.