What makes us sleepy after Thanksgiving dinner?

Answer

That's what happens when you eat too much turkey, mashed potatoes, beans, and gravy.

Scientists believe that the tryptophan in the turkey (an essential amino acid found in poultry) triggers sleepiness by increasing the levels of serotonin and/or melatonin in the brain.

It's also possible that the environment surrounding the dinner itself (spent in a cozy and trusting family environment, generally after a day of football, cooking and other activities) also lends itself to drifting to sleep.