Tryptophan is not what puts you under at Thanksgiving. It’s the carbohydrates

Every year I have promise myself I’m not going to eat myself into a food coma: I eat responsibly, fill my stomach with salad and chomp on the turkey and gravy. Instead, I wake up three hours after Thanksgiving dinner, sprawled out like Robinson Crusoe on the living room floor under a pile of my nephews’ toys. My shirt is covered in light brown stains and greasy handprints smear my jeans.

What is it about Thanksgiving that sends me—and millions of other Americans—into digestive oblivion? Are we all turkey-happy, or is there another reason Thanksgiving is a holiday for sloths?

You’ve probably heard that turkey meat is dripping with a sleep-inducing chemical called tryptophan. And while it’s true things play a role in sending your brain to sleep, saying it does it on its own is like saying Neil Armstrong jumped to the moon all by himself.

First, turkey is not particularly loaded with tryptophan. Ounce for ounce, a roast chicken, grilled steak or a rack of pork spare ribs all have comparable amounts. Freeze-dried tofu has about twice as much tryptophan as turkey, and I doubt you’ll hear your cousin from Southern California complaining about how sleepy he is after eating imitation meat.

Carbohydrates are the real culprit behind Thanksgiving sleepiness. Cast your heavy gaze over to the accessories. Mashed potatoes, cranberry sauce and pie are high in carbohydrates and fill your bloodstream with glucose, a sugar. To regulate the amount of glucose entering your muscles, your body releases insulin, which orders a lot of amino acids to help with the work. Tryptophan is also an amino acid, but not useful for glucose regulation. Instead, most of it is used by the body to make mood-regulating hormones.

Normally, tryptophan has limited access to your brain as it is blocked by other amino acids. But when they are called away to help regulate glucose, tryptophan is out in the open. In the brain it is converted to serotonin and then melatonin – known to cause drowsiness.

Turkey is not special. Any food with a modest amount of tryptophan followed by about 30 grams of carbs (a medium plate of spaghetti) will distract the rest of your amino acids long enough to induce the foggy brain feeling. But the tryptophan/carb combo is only part of the reason for your torpor. What’s more, the fault is that you eat. So. Damn it. Very.