The Truth About Tryptophan

Does tryptophan really make you sleepy -- and is turkey to blame? Experts set the record straight.

From the WebMD Archives

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 niacin, a B vitamin that is important for digestion, skin and nerves, and serotonin. Serotonin is a brain chemical that plays a large role in mood) and can help to create a feeling of well-being and relaxation. "When levels of serotonin are high, you're in a better mood, sleep better, and have a higher pain tolerance," says Elizabeth Somer, MA, RD, author of numerous nutrition books, including her latest, Eat Your Way to Happiness.

Tryptophan is needed for the body to produce serotonin. Serotonin is used to make melatonin, a hormone that helps to control your 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.

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"When is the last time someone ate a chicken breast at a summertime barbecue and thought they felt sluggish [because of it]?" she asks.

Turkey is, indeed, a good source of tryptophan. Still, it's a myth that eating foods high in tryptophan boosts brain levels of tryptophan and therefore brain levels of serotonin, Somer says.

Somer says that proteins like turkey, chicken, and fish, which are high in tryptophan, require assistance from foods high in carbohydrates to affect serotonin levels.

"Tryptophan is quite high in milk and turkey, but that's not the food that will give you the serotonin boost," she says. It's a small, all-carbohydrate snack -- no more than 30 grams of carbohydrates -- in combination with the tryptophan stored in your body from food you've already eaten that will give you the biggest boost of serotonin, Somer says.

A serotonin-boosting snack may include a few Fig Newtons, half of a small whole wheat bagel with honey drizzled over it, or a few cups of air-popped popcorn some time after you've eaten foods high in tryptophan. "Research shows that a light, 30 gram carbohydrate snack just before bed will actually help you 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 blood-brain barrier with a whole bunch of amino acids," Somer says. "It would be like standing in line when the Harry Potter movie comes out and you didn't get in line early enough. The chances of getting in [to see the movie] are pretty slim. That's what happens when you eat a protein-rich food. Tryptophan has to compete with all these other amino acids. It waits in line to get through the 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.

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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.

WebMD Feature Reviewed by Louise Chang, MD on November 18, 2009

Sources

SOURCES:

U.S. Department of Agriculture: "Nutritional Needs of Infants."

Elizabeth Somer, MA, RD, author, Eat Your Way to Happiness.

Vela-Bueno, A. Sleep Medicine Clinics, June 2007; vol 2: pp 303-312.

Joyce Walsleben, PhD, associate professor, New York University Sleep Disorders Center.

Dawn Jackson Blatner, RD, LDN, spokeswoman, American Dietetic Association.

© 2009 WebMD, LLC. All rights reserved.

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