Q. Is turkey’s soporific power fact or fiction?

A. What causes the post-meal need to nap on Thanksgiving? You may or may not be able to blame tryptophan, an amino acid that acts as a precursor to serotonin, the “feel good” central nervous system neurotransmitter. Certain clinical studies indicate that tryptophan in doses of 1 gram or more produces an increased rate of sleepiness in humans.

However, though the holiday bird contains good amounts of tryptophan (about 320 mg per 3.5 ounces), some experts maintain that it is difficult to discern the mood-regulating effects of turkey when it’s served as part of a festive smorgasbord. In order to distinguish any neurological effects (such as after-meal sleepiness), turkey would have to be consumed alone on an empty stomach. And other amino acids in the meal may actually cancel out the effects of tryptophan. What’s more, the other elements of a typical holiday meal may be equally to blame. Carbohydrate-rich dishes such as sweet potatoes, stuffing, bread, and pumpkin pie have also been found to increase levels of tryptophan in the brain.

Although scientists have linked tryptophan to sleepiness, foods such as chicken, ground beef, cheese, and pork loin contain at least as much tryptophan as turkey—yet they have not earned the same reputation. Some experts contend that after-dinner fatigue is more likely the result of overeating, which causes blood to pool in the stomach for digestion and subsequently decreases blood flow to the brain. Alcohol could be another culprit because it depresses the central nervous system. And no one will deny that a long day toiling in the kitchen can make even the most experienced cooks sleepy.

Whatever the cause of drowsiness, keep the Zs at bay by taking an after-meal stroll, which will increase circulation to your muscles and burn off a few of those calories to boot.

This Ask the Expert was written by Victoria Shanta Retelny, RD, LD, president of LivingWell Communications, a nutrition consulting company in Chicago. She also practices medical nutrition therapy at Northwestern Memorial Hospital Wellness Institute.