The Real Reason You Feel Tired After Eating

We have all experienced something like this: You have plans to go out with friends after you eat, but once you've finished your meal, you're just too tired. This can be pretty confusing, and may even seem counterintuitive. If anything, you would think that the nutrients in food would leave you feeling energized, not sleepy. Oftentimes, though, this just isn't the case.

A 1995 study published in Sleep found that people who enjoyed liquid carbohydrate meals for lunch took much longer midday naps than did participants who ate no lunch at all. This phenomenon isn't exclusive to humans: A 2016 study (via eLife) discovered that fruit flies tend to sleep for up to 40 minutes after eating. On average, flies who ate more slept for a longer period of time.

As William Ja, an associate professor of neuroscience at the Scripps Research Institute in Florida, tells Health, the fact that this behavior is seen across species suggests that it serves "some important biological function."

Theories about why we get tired after eating

Nobody is sure exactly why we get sleepy after eating, but experts have a number of theories. Some believe that animals are wired to feel alert when hungry so that they can find food, and that this alertness dissipates after they eat enough, leading to feelings of fatigue (via Worm).

On a biological level, a common theory is that digestion uses up a lot of energy. As dietitian Melissa Prest told Prevention, "It kind of works like this: The food goes in and starts going along on a conveyor belt. Different machines are at work to break down the food, packaging it for specific purposes and shipping it to places that help your body continue to do its work. Obviously, this takes a lot of energy, which can make someone feel tired." Prest adds that post-meal tiredness could also be because insulin levels spike while we are eating and then decline after we are finished.

Regardless of why and how we feel tired after eating, experts agree that it is a natural phenomenon and that the fatigue should not last long.