ABSTRACT: Rumors fly fast—and bad reputations are hard to shake. When it comes to a p.m. Turkey Day lull, we repeat what we’ve heard, and point a finger at the turkey. L-tryptophan—an essential amino acid present in protein-based foods like the traditional Thanksgiving meat—causes a bodily reaction that brings on the Sand Man, we say. Therefore, it’s not the amount of food you eat, but what you eat that makes you want to hit the hay. Right?
HYPOTHESIS: Conventional wisdom doesn’t paint the entire picture: Something besides your bird could be making you droopy eyed.
METHODS: Let’s take a more in depth look at l-tryptophan. Since your body can’t make it, you have to consume it, says Brooke Schantz, R.D., M.S., of Loyola University Medical Center. Foods like oats, milk, eggs, soybeans, and poultry are your best bets. But line these foods up and you’ll see that turkey doesn’t pack the highest numbers. In fact, the amount of l-tryptophan in turkey is similar to the amount in other poultry, says Schantz. Per gram, soybeans or cheddar cheese pack more, but they avoid the heat because they’re not the main stars of Thanksgiving.
Why do you need l-tryptophan? To make B vitamin niacin (which keeps your nervous and digestive systems, skin, and eyes healthy) and also serotonin—a neurotransmitter that helps regulate mood. You can get it through supplements—though in 1991 the U.S. temporarily banned the sale of the supplements due to an outbreak of disabilities and deaths traced back to a Japanese manufacturer. Today, it’s available again in its original form. But the FDA still warns that clinical studies about its effectiveness in treating conditions like insomnia and even depression remain inconclusive.
So then what’s all the talk about tiredness?
RESULTS: When L-tryptophan makes serotonin, serotonin makes melatonin—the sleep hormone known to cause drowsiness and tell your body that it’s time to turn out the lights. But noshing on turkey alone isn’t enough to make you hit the sheets. Here’s why: There are three degrees of separation between the turkey that hits your taste buds and the creation of melatonin, says Schantz. Even more: The amount of l-tryptophan in the bird may not create enough melatonin to cue sleepiness, she says.
DISCUSSION: Consider the accomplices: some popular guys named carbohydrates. Some studies (like a recent one from the American Journal of Clinical Nutrition) find that carb-based meals high on the glycemic index—which measures how quickly blood sugar rises after eating—shorten sleep onset time. In other words, eat foods like mashed potatoes, white bread, or stuffing, and you’ll want to sleep—stat. That’s because your body digests these foods quickly. Sugar floods your bloodstream for a surge of energy, then the opposite happens: a speedy decline of energy.
Eat these foods with turkey and you’re fueling your body’s crash even more. Studies have shown that when you eat carb-packed foods, your body can absorb more l-tryptophan. See, the insulin-related response that comes from a carb load stimulates the uptake of certain amino acids into your muscles—but not l-tryptophan, says Schantz. That means there’s more l-tryptophan in your bloodstream, and more to break the blood-brain barrier fueling that serotonin to melatonin response.
CONCLUSION: The process of producing melatonin through l-tryptophan and turkey may play a role in sleepiness—especially if you’re loading your plate with the bird and carbs. But it really comes down to the carbs. Schantz draws the bottom line: “If you’re feeling sleepy on Thanksgiving, it’s because you ate too much—not because you ate too much turkey.”