Singh says post-meal fatigue occurs for three reasons. “The first is that blood flow is diverted to your GI tract to help digest food and absorb nutrients which leaves less blood flow for the brain and muscles which can make you feel tired.” The second reason why you can become tired after a meal is that your body releases insulin to handle the glucose released into your blood. You could feel drained because your body needs energy for this process to take place.
“[The] third mechanism is that eating increases serotonin levels which is a neurotransmitter responsible for relaxation and sleepiness,” Singh explains. “All these processes compound on one another which can promote post-meal fatigue.”
According to the Sleep Foundation, certain foods will make you more sleepy. Turkey is famous for its fatigue-inducing tryptophan, but milk, bananas, and oats also have tryptophan. While just eating a few ounces of turkey won’t serve as a nighttime lullaby, carbohydrates such as bread enhance tryptophan’s effects.