Tryptophan is an amino acid found in food that can help increase the production of serotonin (Translation: it helps you sleep).

Tryptophan in turkey gets blamed for everyone feeling sleepy after a big Thanksgiving meal. However, it has been wrongfully accused.
The truth is that tryptophan works best on an empty stomach (probably not the case after Thanksgiving), and that there is roughly the same amount of tryptophan in chicken, pork, and cheese. So, you shouldn’t feel more tired after eating turkey than you would after eating chicken.
What probably does make you feel tired on Thanksgiving are the fats, alcohol, relaxation, and carb-loading.
Don’t believe me? Check my sources:
http://recipes.howstuffworks.com/question519.htm
http://chemistry.about.com/od/holidaysseasons/a/tiredturkey.htm
http://www.webmd.com/news/20071220/7-common-medical-myths-debunked
Thanks for these facts. Now pass me another plate of turkey…