Tryptophan in turkey has become almost as famous as the bird's white and dark meat. So has the legend of its power to make people sleepy.
But does Thanksgiving turkey actually induce drowsiness?
"No more so than tuna fish. It's a myth," Dr. Marc Eisenberg, a clinical cardiologist and associate professor of medicine at the Columbia University Medical Center in New York, tells TODAY.com.
"People are sleepy after Thanksgiving because of all the other stuff including the alcohol and just eating too much food."
Still, the myth persists.
NBC News Health and Nutrition Editor Madelyn Fernstrom suspects it really took off after a 1997 “Seinfeld” episode that featured Jerry and George scheming to make a woman fall asleep so they could play with her antique toy collection.
After they treat her to a big turkey dinner, complete with a box of red wine and lots of heavy gravy, she’s soon snoozing on the couch.
Trytophan is specifically mentioned by the characters as “that stuff in turkey that makes you sleepy.” But that’s not quite accurate.
What is tryptophan?
Trytophan is one of the amino acids, which the body uses to make proteins to help it grow and repair tissue, according to the National Library of Medicine.
The body can’t produce tryptophan, so you must get it from your diet, it notes. Turkey is a good source, but so is cheese, chicken, fish, milk, peanuts, egg whites and soy beans. Tryptophan can also be found in sunflower, pumpkin and sesame seeds.
Amino acids do more than just build muscle — some of them are the “starter” compounds for brain neurotransmitters, Fernstrom says.
“Tryptophan can become serotonin — the brain chemical that calms, causes sleep, among other things — if the right enzymes are around to do so,” she notes.
The body also uses tryptophan to make melatonin, which helps regulate the sleep-wake cycle, according to the National Library of Medicine.
Eating more tryptophan in high-protein foods like turkey does increase the tryptophan going into your bloodstream, but that doesn’t mean your body will turn it into serotonin.
Other amino acids are competing with tryptophan to get into the brain using the same entry “door” and because there are many more of these other compounds than tryptophan, there‘s no impact on serotonin levels with a protein meal like roast turkey, Fernstrom says.
You’d have more success if you were to eat just mashed potatoes or rolls at Thanksgiving dinner: The way to get more tryptophan into the brain and boost serotonin production is by eating pure carbohydrate, she explains. That releases insulin, which lowers the levels of other amino acids, so tryptophan has a chance to get in to the brain without competition.
Why does turkey make you sleepy?
Many people do get very drowsy after consuming a huge Thanksgiving meal. The average dinner can contain 3,000 calories, according to the Calorie Control Council. Don’t blame the turkey for making you sleepy, though.
“That’s due to changes in metabolic activity during digestion. The body has signals to ‘slow down’ and digest the food as a priority,” Fernstrom says.
“And there are changes in glucose and insulin balance that can impact the brain and the digestive system.”
Add the stress of hosting or attending a Thanksgiving dinner, the lack of sleep during the journey to get there, free-flowing alcohol and all the sitting around in front of the TV afterward, and you have the perfect formula for dozing off.
The best solution to stay more alert is to moderate your meal. Cardiologists suggest making plant-based side dishes as the main dish instead of eating a huge portion of turkey. They also advise skipping turkey skin, butter and gravy.
And don’t overdo it on the wine. Stick to one or two drinks, or avoid alcohol altogether.