L-Tryptophan: Does Turkey Really Make You Sleepy?

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Every year at Thanksgiving, most of us engage in an annual rite of passage: stuffing ourselves mercilessly with turkey, cranberry sauce, and pie. Not a bad way to spend a Thursday. But inevitably, in that hour between feeling so full you think you’ll explode and gearing up for round two with the leftovers, your relatives can find you conked out on the couch.

Along comes Aunt Mildred with her armchair scientific explanation. You’re tired, she tells you, because the turkey you just ate is laden with L-tryptophan. Tryptophan, she says, makes you tired.

So is your aunt right? Is the turkey really what’s to blame for Thanksgiving sleepiness? The experts helped WebMD sort out the facts.

What is L-Tryptophan?

L-tryptophan is an essential amino acid. The body can’t make it, so diet must supply tryptophan. Amino acids are building blocks of proteins. Foods rich in tryptophan include, you guessed it, turkey. Tryptophan is also found in other poultry, meat, cheese, yogurt, fish, and eggs.

Tryptophan is used by the body to make sleep and wake cycles.

Turkey the Sleep Inducer?

As it turns out, turkey contains no more of the amino acid tryptophan than other kinds of poultry. In fact, turkey actually has slightly less tryptophan than chicken, says Dawn Jackson Blatner, RD, LDN, an American Dietetic Association spokeswoman and author of The Flexitarian Diet.

Jackson Blatner says that if we’re sleepy on Thanksgiving as a direct result of eating turkey, then eating other foods rich in tryptophan should have the same effect.

“When is the last time someone ate a chicken brain levels of tryptophan and therefore sleep better,” Somer says.

Amino Acid Overload

When you eat foods rich in tryptophan, as the food digests, amino acids – not just tryptophan – make their way into the bloodstream. This causes competition among the various amino acids to enter the brain.

“Tryptophan, which is a bulky amino acid, would have to stand in line to get through the -brain barrier with a whole bunch of amino acids,”>blood-brain barrier and very little of it makes it across.”

The small, all-carbohydrate snack is tryptophan’s ticket across the blood-brain barrier, where it can boost serotonin levels. So have your turkey, Somer says, because it will increase your store of tryptophan in the body, but count on the carbohydrates to help give you the mood boost or the restful sleep.

“It’s the all-carb snack that ends up being like a sneak preview of the [Harry Potter] movie, where no one else knows it’s showing,” she says.

Too Much of a Sleepy Thing

Is it possible to have too much tryptophan in the body? Not really, Somer says. “Except if you end up eating a lot of tryptophan, it means you’re eating a lot of protein and Americans already eat a lot of protein. It’s the only nutrient we get too much of,” she says.

“If you’re getting even one serving of 3 ounces of meat, chicken, or fish; a couple of glasses of milk or yogurt; or if you’re eating beans and rice, you will get all the amino acids you need and in there will be the tryptophan,” Somer says.

Thanksgiving Grogginess: Look Beyond the Turkey

So if eating turkey isn’t exactly the same as popping a sleeping pill, why the sudden grogginess as soon as our holiday feast is over?

“It boils down to Thanksgiving being a time when people overeat,” Jackson Blatner says. “When people overeat food, the digestion process takes a lot of energy. Don’t incriminate the turkey that you ate,” she says of post-Thanksgiving meal exhaustion, “incriminate the three plates of food that you piled high.”

And let’s not forget that the holidays generally mean time off from work and with family. Many people feel more relaxed to begin with (family wars not withstanding). Add alcohol to the mix, and voila! Sleep!

Speaking of sleep, Joyce Walsleban, PhD, associate professor at New York University’s Sleep Disorders Center, suggests we all get plenty of it. “Coming up on the holidays and trying to get all the things done that one would normally be doing, you short cut your sleep and that’s never helpful. By the time the holiday comes, everyone has gotten sick.”

At least then you’ll have a good excuse to lay down and take a nap.