Why do big meals make us sleepy?

Thanksgiving Day is coming up and we are all ready for a yummy feast! But, have you ever wondered if calories give us energy, why do big meals make us sleepy? This contradictory experience is a common one, and that goes double on Thanksgiving, where on average one can eat up to 3,500 calories in a single meal! And, while many people blame the turkey's tryptophan for their tiredness, the truth is that other foods have just as much of the same sleep-inducing amino acid. It turns out that a few factors conspire to make the Thanksgiving meal the sleepiest yet. For one, high-carb, high-fat and high sugar foods (like mashed potatoes and pumpkin pie) trigger a neural response as soon as they hit the small intestine. That response, in what's called the parasympathetic nervous system, tells our body to slow down and focus on digesting rather than getting more food. Add to that a few hormonal shifts that happen in the body after a large feast, and you've got a recipe for “food coma.”

The molecular composition of tryptophan.