That third slice of pizza was exactly what you needed. But, in a scenario that's all too familiar, all that hunger will inevitably be replaced by a distinct craving for a nap. So what is it that causes that seemingly inescapable sleepiness after you scarf down a giant meal? It turns out your food comas are made possible by some complicated digestive biology.A food coma (technical term: "postprandial somnolence") is a condition in which you may feel drowsy, lightheaded, or fatigued after eating a large meal. You may experience it as falling asleep a cool 20 minutes after your Thanksgiving dinner or as a need for a midday nap after a lunchtime Shake Shack run. Although it's normal every once in a while, you may want to check in with a doctor if you're consistently fatigued after eating, as this can be an early sign of diabetes You might be surprised to know that there's a pretty direct line between the urge to sleep and what you eat. For example, experts often recommend snacking on complex carbs, lean protein, and certain fruits and veggies when you're near bedtime. That's partly because many of those nutritious foods (e.g. chicken breast) contain tryptophan , an amino acid your body needs to make the sleep-inducing hormone serotonin. Others, such as cherries, contain melatonin, another hormone that can lull you to sleep.But there are some other complex hormonal cues during digestion that, when overloaded, can lead to a food coma. For one thing, when you eat carbohydrates, your body breaks them down into a form of sugar for energy and releases insulin in order to store up that sugary energy for later. An insulin spike can definitely cause feelings of fatigue , but the hormone also helps shepherd tryptophan into your brain. So that pile of fries will usher in an afternoon nap in more than one way.And on top of that, as food makes its way through your body, your stomach is releasing gastrin and your intestines are releasing their own series of hormones. Together these chemicals help regulate the flow of your delicious digestive juices and, down the line, blood flow to the GI tract. As more blood makes its way down there, you may start to feel a little sleepy, especially if you've just eaten a giant meal.However, it's just a myth that your gut "redirects" blood from your brain for this complicated task. In fact, pretty much everything about the blood in your brain is tightly regulated by other bodily processes (perhaps even yawning ). So exactly how much of a difference this makes for your energy levels has been disputed. But all of this means that if you're looking to avoid a food coma, you're going to want to stick with smaller meals that are rich in both protein and complex carbs, but low on greasiness. And to help your body digest all that, try not to fall into the nap trap after a meal. Instead, get moving — a short walk is enough, we swear. Plus, that will also help you avoid heartburn and any uncomfortable bloating . Until next time, anyways.