“Eating turkey makes you sleepy because of tryptophan”

The idea that a holiday turkey dinner inevitably leads to a sleepy stupor because of tryptophan is a widely held belief, but it’s actually a common misconception. This myth likely gained popularity in the late 1960s and 70s, stemming from scientific studies that identified tryptophan, an essential amino acid, as a precursor to serotonin and melatonin—neurochemicals associated with relaxation and sleep. However, popular media and some non-specialist interpretations exaggerated these findings, incorrectly singling out turkey as an exceptionally rich source of this "natural sleeping pill."

In reality, turkey contains no more tryptophan than many other common protein sources like chicken, beef, or cheese; some sources even suggest it has slightly less than chicken. For tryptophan to significantly impact brain serotonin and melatonin levels and induce sleepiness, it needs to cross the blood-brain barrier. When consumed as part of a protein-rich meal, tryptophan must compete with many other amino acids for entry, limiting its absorption into the brain. While large supplemental doses of pure L-tryptophan (1 gram or more) can promote sleep, the amount naturally present in a typical serving of turkey is far too small to have such a sedative effect.

The real reasons behind that irresistible urge to nap after a big celebratory meal are far more complex and involve several factors. Overeating, especially large portions of foods rich in carbohydrates and fats, demands a substantial amount of energy for digestion, diverting blood flow to the digestive system and away from the brain. Carbohydrates, in particular, cause an insulin spike which helps clear other amino acids from the bloodstream, indirectly making it easier for the modest amount of tryptophan to enter the brain. Furthermore, the consumption of alcohol, a central nervous system depressant, significantly contributes to drowsiness and amplifies post-meal fatigue.