Every year, many of us gather around a Thanksgiving table and stuff our faces with food before ducking out of awkward conversations with distant relatives by blaming our post-feast food coma on "too much turkey." It's true that there is no slumber quite like that of a Thanksgiving nap, but it's time we faced what's really turning us into drooling zombies who overstay our welcome on some second cousin's couch. And guess what? It's not the turkey that makes you sleepy.

For starters, turkey may be loaded with tryptophan, the amino acid that's a precursor to the sleep-inducing serotonin, but so is just about any high-protein food. Cheese, nuts, and, yes, even Tofurkey all have way more tryptophan than turkey and many other meats. More importantly, tryptophan by itself doesn't really make you tired. Foods laden with this amino acid are also loaded with a bunch of other amino acids that block your brain from absorbing the tryptophan and turning it into the sleep-inducing serotonin. A psychiatrist named John Fernstrom looked into this back in 1972 and found that, "The main determinant of brain tryptophan and serotonin concentrations does not appear to be...tryptophan alone." Rather, it's the presence of good ol' delicious carbs that helps your body convert that tryptophan into serotonin. And let's be real here—Thanksgiving isn't really about the turkey. It's about the carbs.

When you mix tryptophan with generous helpings of mashed potatoes, bread, and pie, it floods your body with sugars. Suddenly, all those other amino acids that were blocking your brain from absorbing that tryptophan suddenly have a new job: helping your body break down all those sugars. Without anything to stop it, the brain starts converting that tryptophan into serotonin, which ushers in those warm, sleepy feels.

What really seals your fate in dreamland, however, is the fact that you probably just ate way too much food. Regardless of whether you even ate any turkey, eating large portions of anything will leave your body with a ton of food to digest. That takes up a lot of energy, so while your innards are doing their work, your brain is signaling to the rest of your body that it's time to take it easy and reserve energy.

This happens whether you want it to or not because the same part of your body that tells your heart to beat and your lungs to breathe also tells your body to digest. It's called your parasympathetic nervous system, and it automatically queues up tasks that are necessary for survival. In order to successfully take in and process all of those nutrients you've just scarfed, that system goes into hyperdrive. So while you might feel guilty dodging the dishes, at least you can say one part of you is working hard.

Besides, you've likely just endured hours of horrible traffic, jet lag, day drinking, endless cooking, and/or a series of tense and circular political discussions all in the name of gratitude. So go ahead—loosen that drawstring, kick off your shoes, and post up. You've earned it, ya big glutton.