Every year at Thanksgiving, most of us engage in an annual rite of passage: stuffing ourselves mercilessly with turkey, cranberry sauce, and pie. Not a bad way to spend a Thursday. But inevitably, in that hour between feeling so full you think you'll explode and gearing up for round two with the leftovers, your relatives can find you conked out on the couch.

Along comes Aunt Mildred with her armchair scientific explanation. You're tired, she tells you, because the turkey you just ate is laden with L-tryptophan. Tryptophan, she says, makes you tired.

So is your aunt right? Is the turkey really what's to blame for Thanksgiving sleepiness? The experts helped WebMD sort out the facts.