Tryptophan is an amino acid that is present in proteins. Tryptophan is actually an essential amino acid as we have to have it to sustain life.
Tryptophan is found in many foods such as poultry, chocolate, milk, yogurt, cheese, eggs, and nuts.
We often hear that it is the tryptophan in turkey that makes us sleepy on Thanksgiving, however turkey actually has the same amount of tryptophan as chicken, and less than many other foods such as eggs, cheese, or even sunflower seeds!
So why do we get sleepy on Thanksgiving? Any big meal that contains tryptophan and lots of carbohydrates can make us sleepy, not just turkey. Also, the combination of taking a break from hard work, as well as alcohol, are likely contributing factors.