That feeling of sleepiness after eating is called postprandial somnolence.

Postprandial somnolence can be attributed to a few different things. Some of the foods you eat can release certain hormones that may make you tired. When you eat can also contribute to feeling fatigued. And how much you eat can play a role, too.

It’s common to feel tired after eating a meal, especially if it’s a meal full of carbohydrates and protein.

“It takes between 30 to 40 hours to digest a meal,” says Zumpano. “Your body’s working all the time to digest food. It’s already digesting food to begin with, and then you put more food in there. And if it’s a heavy meal, it’s just going to bog down your system.”

Hormones also play an important role in your digestion.

“Some researchers believe that people feel tired after eating because their body’s producing more serotonin,” says Zumpano. “Serotonin is the chemical that regulates mood and sleep cycles.”

Tryptophan is an essential amino acid found in protein-rich foods like chicken, eggs, cheese and fish. Tryptophan helps your body produce serotonin.

“Oftentimes, when you’re eating a meal rich in carbohydrates and protein, you may feel sleepier because you have an uptake of tryptophan from the protein and then an increase of serotonin,” explains Zumpano.

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