The amino acid commonly associated with sleepiness after a traditional Thanksgiving dinner is tryptophan. Tryptophan is an essential amino acid, meaning the human body cannot make enough of it and must obtain it from food.
The Thanksgiving connection is largely a popular oversimplification. Turkey does contain tryptophan, but it is not uniquely rich in the amino acid; foods such as chicken, cheese, eggs, soy, and nuts also provide it. After digestion, tryptophan can contribute to the production of serotonin and melatonin, chemicals involved in mood and sleep regulation.
The heavy meal itself is usually a more important explanation for post-dinner drowsiness. Large portions of carbohydrates, alcohol, reduced activity, and the body’s normal afternoon or evening circadian dip can all make people sleepy. Tryptophan is therefore the standard quiz answer, but turkey alone is not generally responsible for Thanksgiving fatigue.