Turkey does not make you sleepy.

While it's true that turkey is a good source of L-tryptophan, an essential amino acid that helps the body to produce serotonin, it is also present in other foods such as chicken and milk.  Any tired feeling experienced is more likely due to eating excessive amounts of high fat, high sugar foods.

What Is L-Tryptophan?

L-tryptophan is an amino acid that is essential for normal growth in children and balances nitrogen in adults.  The body uses tryptophan to make serotonin and niacin. In order for tryptophan to produce niacin the body requires adequate amounts of iron, riboflavin, and vitamin B6.

The body cannot make tryptophan itself and must get it from food sources which include turkey, chicken, fish, cheese, eggs, milk, nuts, peanuts, peanut butter, soy, tofu, pumpkin seeds, and sesame seeds.

What Is Serotonin?

Tryptophan is part of the biochemical process by which serotonin is made.  Serotonin is a neurotransmitter that helps relay messages from one area of the brain to another.  Serotonin is believed to affect a variety of functions in the body such as mood, relaxation, sexual desire, memory, temperature regulation, cardiovascular function, muscles, and milk production.