“Eating turkey makes you sleepy because of tryptophan”

The idea that the tryptophan in turkey is solely responsible for post-meal drowsiness, particularly after holiday feasts, is a widespread misconception. This myth likely originated from the understanding that tryptophan, an essential amino acid, is a precursor to serotonin and melatonin, two brain chemicals known to regulate mood and sleep. Because turkey contains tryptophan, it became the convenient, albeit incorrect, culprit for the "food coma" many experience.

However, scientific evidence reveals that turkey contains no more tryptophan than other common protein sources like chicken, beef, or even cheese. In fact, some foods, such as soybeans, may contain even higher levels. The amount of tryptophan in a typical serving of turkey is simply not enough to have a sedative effect, especially since it competes with other amino acids for entry into the brain. For tryptophan to significantly impact sleep, it would need to be consumed in much larger doses, often on an empty stomach, or in amounts far exceeding what a normal meal provides.

The true reasons behind the sleepy feeling after a large meal, like a Thanksgiving dinner, are more complex and multifaceted. Overeating, especially large quantities of carbohydrates found in sides like stuffing and mashed potatoes, triggers an insulin spike. This insulin surge clears most amino acids from the bloodstream, giving tryptophan a clearer path to the brain, where it can then contribute to serotonin and melatonin production. Additionally, alcohol consumption, often accompanying such meals, acts as a depressant and further contributes to drowsiness. The overall digestive effort required for a heavy meal, combined with a relaxed environment, also shifts blood flow to the digestive system, diverting energy from the brain and leading to a feeling of lethargy. People commonly believe the myth because the association between turkey and tryptophan is widely circulated, and the experience of post-meal sleepiness is a relatable one, making the simple explanation seem plausible.