Why do we feel tired after eating?

Feeling sleepy after a big meal, formally known as postprandial somnolence, has several overlapping causes. Digesting food, especially a large or carbohydrate-rich meal, raises blood sugar and then insulin, which can influence brain chemicals that make you drowsy. Meals high in the amino acid tryptophan, found in foods like turkey, eggs, and cheese, can increase production of serotonin and melatonin, which promote calm and sleep. Eating also activates the rest-and-digest branch of the nervous system, slowing the body down. The common belief that blood is dramatically diverted from the brain to the stomach is largely a myth, but the hormonal and blood-sugar effects are real. Larger meals and simple carbohydrates tend to cause the strongest drowsiness.