This Thanksgiving, millions of Americans will dine around their family table, stuffing their faces full of turkey, ham and holiday side dishes. And shortly after that meal, many Americans will suffer from drowsiness, and many will take a nap after their big meal.

But what actually causes that sleepiness?

Many believe that the turkey is to blame because it's high in tryptophan, which makes the brain sleepy.

There's just one problem with that theory: turkey doesn't contain any more tryptophan than any other meat. In fact, tofu has twice as much tryptophan as turkey.

However, tryptophan does play a part in the nap attack that happens after a big meal. But the real culprit that causes drowsiness after Thanksgiving dinner is carbs. Think about those carb-loaded side dishes: mashed potatoes, rolls, cranberry sauce and pie. Your body responds to those carbs by making lots of glucose.

To deal with the high amounts of glucose in your body after eating all those carbs, your body releases insulin. That insulin uses amino acids to get its job done.

Although tryptophan is technically an amino acid, it doesn't do anything for regulating glucose, but instead, regulates mood hormones in the body. It also has limited access to the brain, as other amino acids block it from going there.

But when those other amino acids leave the brain to help regulate glucose after a big meal, tryptophan gets a free pass. In the brain, it eventually becomes melotonin, which causes drowsiness.

Other factors also play into your post-dinner sleepiness. Before your big meal, you probably indulged in tiresome activities, such as traveling long distances and cooking, and your body is already a little exhausted by the time you sit down at the table. Combine that with a carb-loaded meal and you'll want a nap soon after.

So how can you combat sleepiness after a holiday meal? Load up on protein and go light on the carbs. Yes, the best thing you can do is eat more turkey, instead of less. It's also a good idea to engage in some kind of activity after a big meal, such as taking a walk.

However, Thanksgiving is a holiday, and if you have the day off, who's to say a nap is a bad idea? Eat up and enjoy it: it only comes once a year. Even if you overeat, your body can handle it.

[Photo Credit: Flickr]