Oh, go on. You know you're going to do it.

Every Thanksgiving, you get that woozy, snoozy feeling after the big feast. In some households, jockeying for the best couch position once the table is cleared is practically a contact sport.

Blame it on all that turkey. Right?

Well, maybe not.

"This food coma phenomenon that people may experience after Thanksgiving dinner is real," said Sigrid Veasey, a member of Penn's Center for Sleep and Circadian Neurobiology.

The popular scapegoat is tryptophan, a naturally occurring amino acid in turkey. But according to Veasey, you would have to eat 100 turkeys to get enough tryptophan – about one gram — to make you that sleepy.

The real issue is not so much what you're stuffing into your mouth, but how much.

"What you're eating is actually inducing inflammatory proteins know as cytokines and other substances produced in the body in response to this mega meal," said Veasey, a professor of sleep medicine at Penn.

Eating too much releases those inflammatory molecules in the blood, which then tell your brain to rest.

In addition to cytokines, the excess food lowers wakefulness-promoting neurochemicals and those "get up and go" neural signals in the hypothalamus.

Don't believe it? Veasey suggests you try eating just as much as you normally would on Thanksgiving, but not the turkey. You'll be just as sleepy, Veasey said.

And it isn't just the big meal itself that can make you feel out of sorts.

Penn researchers found that a "delayed eating lifestyle" – such as skipping breakfast, making lunch your first meal, and loading up at dinner, which a lot of people do on holidays – disrupts the body's natural circadian rhythm. That's the cycle that tells us when to sleep, wake, and eat, and affects our hormones and other bodily functions.

Other Penn research has shown that delayed eating increases weight, adversely affects fat metabolism, and increases glucose, insulin, triglycerides and cholesterol – all of which are implicated in an increased risk of obesity, diabetes, heart disease and other health problems.

Last month, Penn received a $3.75 million, five-year grant from the National Institute of Diabetes and Digestive and Kidney Diseases to continue its research into how meal times influence health. Soon we may know even more.

Of course, there's still Thanksgiving.

It's one day. Maybe breakfast can wait.