February 23, 2019
Does Turkey Really Make You Sleepy?

Does Turkey Really Make You Sleepy?

by Densie Webb Ph.d., R.d.  

The claim: Turkey makes you sleepy.

The facts: This claim likely originated from the stupor-like state many of us experience after a Thanksgiving (or other holiday) meal in which turkey is typically the centerpiece. It was reinforced by a Seinfeld episode in the 1990’s, in which George and Jerry tried to put someone to sleep by stuffing them with turkey.

Here’s some background that has helped fuel the myth: Turkey contains the essential amino acid tryptophan, which can enter the brain by crossing the blood-brain-barrier, where it is converted to the neurotransmitter serotonin. Serotonin has a calming effect and helps regulate sleep, and it is a precursor to the hormone melatonin, which also is associated with sleep.

In addition, some research has found that tryptophan supplements, sold as sleep aids, help people fall asleep faster (but don’t help them sleep longer)—though overall the evidence of benefit in human trials is limited and inconsistent and there are safety concerns about the supplements, especially when they are taken at high doses.

Here’s where the myth doesn’t quite add up: Taking tryptophan by itself—as in supplements—would open the entry gate to the brain, but no food contains tryptophan alone. Turkey contains other amino acids besides tryptophan, and all of them compete for entry into the brain. The journey of the tryptophan in turkey across the blood-brain-barrier can be likened to being a passenger on a crowded bus, where everyone is vying for a seat. The presence of other amino acids makes it less likely that a significant amount of tryptophan will find a seat and successfully make its way into the brain.

Moreover, the conversion of tryptophan to serotonin can occur when you eat any tryptophan-containing food, not just turkey—and lots of other foods provide even more tryptophan per ounce than turkey, including some cheeses, bacon, pumpkin seeds, oat bran, and tofu. Yet it’s unlikely that any of these foods have you snoozing when you’re done.

Rather, that after-turkey lull is more likely due to the large amount of carbohydrates consumed in a typical Thanksgiving-day meal (think about all that stuffing, gravy, potatoes, rolls, and pie, for example). Carbs trigger the release of insulin and the uptake of amino acids into muscles—all except for tryptophan. Though carb-rich foods themselves contain little or no tryptophan, they paradoxically reduce competition by other amino acids to enter the brain, allowing more tryptophan—from turkey or other foods—to cross the blood-brain-barrier and be converted to serotonin.

Another likely culprit is the sheer volume of food consumed at big meals where turkey is served. After a large meal, blood pressure may drop (called postprandial hypotension), which can cause sleepiness (as well as nausea). And then there is the wine often served at holiday meals, which could also have you nodding off.

Bottom line: Your turkey is not guilty as charged—at least not directly. It’s much more likely that you feel sleepy due to the heavy load of carb-rich foods, general overindulgence, and alcohol associated with big turkey meals.

Also see Bread: Is the Crust Really the Most Nutritious Part?