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The Truth About Tryptophan

Does tryptophan really make you sleepy -- and is turkey to blame? Experts set the record straight.
By
WebMD Feature
Reviewed by Louise Chang, MD

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.

"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.

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