Turkey Culprit for Thanksgiving Snoozes?

Will that serving of Thanksgiving turkey put you to sleep?

Every year, tryptophan, a chemical found in turkey, gets the blame. But CBS News medical correspondent Dr. Jennifer Ashton says that it's actually not the culprit.

Tryptophan, Ashton explained, is an essential amino acid found not just in turkey, but also in chicken, peanut butter, cheddar cheese and even milk.

"But," she told "Early Show" co-anchor Maggie Rodriguez, "It's not the major reason everyone passes out after they stuff themselves on Thanksgiving."

It's true, Dr. Ashton continued, that tryptophan in isolation can make you sleepy, because it triggers something called serotonin, a "feel-good" hormone that's made in the brain. But it doesn't work in isolation -- and when it comes to Thanksgiving, many other things can make you drowsy, including the massive amount of carbohydrates that many people eat during the holiday.

Co-anchor Harry Smith had another theory: He pointed to the wine that is often consumed with Thanksgiving dinner.

"I agree with that, too. But there's even a better theory," Dr. Ashton said. "Anytime you eat, a lot of your body's blood flow goes to your stomach, to your digestive tract, to help absorb and process that meal. And that, therefore, is not going to your brain. So, again, the more you eat, the more blood flow is going to your stomach."

She also mentioned another possible factor that has less to do with what's been eaten: After Thanksgiving dinner, many people go sit on the sofa, which can also bring on the desire to nap.

"What can we do to avoid getting sleepy? Or, do we just deal with it?" Rodriguez asked.

"First of all, I think that's part of the fun of Thanksgiving, taking that nice little nap," Dr. Ashton said. "But, if you're cleaning up the kitchen, it's hard to be tired and fall asleep."

She also offered a suggestion for keeping the drowsiness at bay -- get off the sofa and head outside. "Take a nice walk, throw the football around before you watch the football on TV, all those things are good ideas."