Why do we feel sleepy after a big meal?

Eating a big meal triggers the parasympathetic nervous system, which promotes rest and digestion. Blood flow shifts toward the stomach and intestines to absorb nutrients, slightly reducing supply to the brain and muscles. Carbohydrate-rich meals boost the amino acid tryptophan’s entry into the brain, where it is converted into serotonin and then melatonin, both linked to sleepiness. The gut hormone cholecystokinin (CCK), released during fat digestion, also signals feelings of fullness and drowsiness. Eating moderately, choosing meals lower in refined carbohydrates and taking a short walk can help reduce the post-meal slump.