Every year, I promise myself I'm not going to get eat myself into a food coma: I'll eat responsibly, front load my belly with salad and go light 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 hand prints smear my jeans.

What is it about Thanksgiving that sends me—and millions of other Americans—into digestive oblivion? Are we all blissed out on turkey, or is there another reason Thanksgiving is the holiday for slothiness?

You've probably heard that turkey meat is dripping with a sleep-inducing chemical called tryptophan. And while it's true the stuff plays a part in sending your brain into slumber, saying it does so single-handedly is like saying Neil Armstrong jumped to the moon all by himself.

For one thing, turkey isn't particularly laden with tryptophan. Ounce for ounce, a roast chicken, grilled steak, or rack of pork spareribs all have comparable amounts. Freeze-dried tofu has about double the amount of tryptophan as turkey, and I doubt you'll hear your cousin from southern California complain about how sleepy he is after gorging on faux-meat.

Carbs are the real culprits behind the Thanksgiving sleepies. Cast your heavy-lidded gaze over to the side dishes. Mashed potatoes, cranberry sauce, and pie, are carb-rich and load your bloodstream with glucose, a sugar. In order to regulate the amount of glucose that makes its way into your muscles, your body releases insulin, which commandeers a bunch of amino acids to help with the job. Tryptophan is also an amino acid, but not useful for glucose regulation. Instead, it's mostly used by the body to make mood-regulation hormones.

Normally, tryptophan has limited access to your brain, as its blocked by other amino acids. However, when they get called away to help regulate glucose, tryptophan is in the clear. In the brain, it gets converted into serotonin, and then melotonin—known to cause drowsiness.

Turkey isn't 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 that foggy-brain feeling. But the tryptophan/carb combo is only part of the reason for your torpor. What's more to blame is the fact that you eat. So. Damn. Much.

When that Thanksgiving bomb lands in your tummy, it starts stirring up activity in something called your parasympathetic nervous system. This is one half of the neural network that controls your unconscious actions, like breath, heartbeat, and digestion. (Its partner, the sympathetic nervous system, is associated with the fight-or-flight response that gets you amped up, for example when you see a table of Thanksgiving goodies.) Also known as the "rest and digest" response, the sense of calm triggered by a big meal is biologically very similar to the drowsiness you feel after sex or a good cry.

And let's be honest, your body has probably been primed for exhaustion for hours before you sat down. Many of us travel thousands of miles to visit family, and our busy American work schedules mean we usually get there without much time to settle into our temporary time zones. Once the mealtime excitement is over, the jet lag can creep in. And if you're hosting, you're bound to be spent from the combined stress of making the meal, fielding a thousand questions, and keeping your red state and blue state relatives from killing each other.

The best way to combat the sleepiness is to eat less Thanksgiving food. Because that ain't gonna happen, the next best option is to load your plate with turkey, and ease up on the gravy, potatoes, and stuffing. A higher protein to carb ratio will cut short the insulin response that allows tryptophan play Mr. Sandman.

For me, that doesn't really work either. The best way I've found to power through a case of the napsies is to get up and do some kind of activity after eating. Volunteer to do the dishes (all of them!). Schedule a post-dinner touch football game. If you're truly desperate for stimulation, take your younger relatives on an pre-Black Friday shopping trip. Or, you can just embrace it, and fall back onto the couch, and into sweet oblivion.