Final answer:
Feeling sleepy after eating turkey at Thanksgiving is often blamed on the amino acid tryptophan in turkey.
Step-by-step explanation:
The tendency to feel sleepy after consuming a large amount of turkey during Thanksgiving is often attributed to the presence of an amino acid called tryptophan found in turkey.
Tryptophan is known to have a relaxing effect and is a precursor to the sleep-regulating hormone melatonin. However, recent studies suggest that the quantities of tryptophan in turkey are not significant enough to cause immediate drowsiness.
It is more likely that the overall high intake of calories, increased consumption of carbohydrates, and perhaps the relaxing atmosphere of the holiday contribute to the sluggishness and desire to sleep after the meal.
Additionally, the parasympathetic nervous system is activated during digestion, especially after a large meal. This activation promotes a 'rest-and-digest' state, which can further explain the feeling of tiredness.
Another contributing factor can be the consumption of alcohol which is common during holiday celebrations and can enhance drowsiness. Therefore, while tryptophan plays a role in sleep, it is probably the combination of a heavy meal, relaxation, and possibly alcohol that leads to the common Thanksgiving nap, more than just the turkey itself.