ABSTRACT: Rumors fly fast鈥攁nd bad reputations are hard to shake. When it comes to a p.m. Turkey Day lull, we repeat what we鈥檝e heard, and point a finger at the turkey. L-tryptophan鈥攁n essential amino acid present in protein-based foods like the traditional Thanksgiving meat鈥攃auses a bodily reaction that brings on the Sand Man, we say. Therefore, it鈥檚 not the amount of food you eat, but what you eat that makes you want to hit the hay. Right?
Something besides your bird could be making you droopy eyed.
HYPOTHESIS: Conventional wisdom doesn鈥檛 paint the entire picture: Something besides your bird could be making you droopy eyed.
METHODS: Let鈥檚 take a more in depth look at l-tryptophan. Since your body can鈥檛 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鈥檒l see that turkey doesn鈥檛 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鈥檙e 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鈥攁 neurotransmitter that helps regulate mood. You can get it through supplements鈥攖hough 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鈥檚 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鈥檚 all the talk about tiredness?
RESULTS: When L-tryptophan makes serotonin, serotonin makes melatonin鈥攖he sleep hormone known to cause drowsiness and tell your body that it鈥檚 time to turn out the lights. But noshing on turkey alone isn鈥檛 enough to make you hit the sheets. Here鈥檚 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 from the American Journal of Clinical Nutrition) find that carb-based meals high on the glycemic index鈥攚hich measures how quickly blood sugar rises after eating鈥攕horten sleep onset time. In other words, eat foods like mashed potatoes, white bread, or stuffing, and you鈥檒l want to sleep鈥攕tat. That鈥檚 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鈥檙e fueling your body鈥檚 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鈥攂ut not l-tryptophan, says Schantz. That means there鈥檚 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鈥攅specially if you鈥檙e loading your plate with the bird and carbs. But it really comes down to the carbs. Schantz draws the bottom line: 鈥淚f you鈥檙e feeling sleepy on Thanksgiving, it鈥檚 because you ate too much鈥攏ot because you ate too much turkey.鈥