The verdict is in. We all need to stop blaming turkey for making us drowsy after Thanksgiving dinner. The real culprit is overeating – and especially what we’re overeating.
Consider what’s on the table besides turkey: Mashed potatoes, stuffing, dinner rolls, yams. What do these foods have in common? They’re all carbohydrates.
Since it’s not unusual to sink into a self-induced coma after stuffing ourselves with carbohydrates, what made everyone think the culprit was turkey?
It’s hard to track down, but a few years ago, someone pointed out that turkey contains tryptophan and tryptophan is a precursor to the production of serotonin, a “feel-good” neurotransmitter in the brain.
However, what they didn’t say is that tryptophan isn’t unique to turkey. It’s one of 20 essential amino acids and many other animal proteins contain just as much tryptophan as turkey does. And they also didn’t say that tryptophan has a hard time even getting to the brain.
Neuropharmacologist Richard Wurtman of the Massachusetts Institute of Technology's Department of Brain and Cognitive Sciences, explains that tryptophan is actually rather scarce. To get to the brain, amino acids have to hitch a ride on specialized transport proteins, and to get on board, tryptophan has to compete with five other amino acids. Because of its relative scarcity, tryptophan gets very few of those available spots.
If taken alone, with no other amino acids present, tryptophan would indeed increase brain serotonin, Wurtman says, but no food source contains tryptophan in the absence of other amino acids.
"Paradoxically, what probably makes people sleepy after Thanksgiving dinner is…dessert," he says. "Eating carbohydrates increases brain serotonin in spite of the fact that there is no tryptophan in carbohydrates."