This May Be Why You Fall Into a Food Coma

Research on fruit flies offered clues about why eating sometimes makes you tired

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The "food coma" is a well-known phenomenon. And it seems the after-dinner snooze effect is real. Still, as of April 2022, scientists didn't know exactly why or how eating leads to sleepiness.

A study from November 2016 on fruit flies offered some potential clues. Turns out fruit flies like to nap after eating, too—especially when they've eaten meals high in protein or salt, or meals that are extra large.

The 2016 study, published in the journal eLife, was the first time "postprandial sleep" (the scientific name for a food coma) had been studied in fruit flies. It's unknown, as of April 2022, whether the findings could apply to humans—but at the very least, they shed light on the overall relationship between eating and sleeping, the authors wrote.

To examine that relationship in fruit flies, scientists from the Scripps Research Institute recorded and analyzed the insects' food consumption and motion, noting that flies tended to sleep for 20–40 minutes after eating. Those who ate bigger portions, and those who ate protein-rich or salty solutions, generally slept the longest. (Foods high in sugar didn't have as big an effect.)

The researchers also looked for specific areas in the brain that were responsible for these prolonged naps. "By using genetic tools to turn neurons on and off in the fly brain, we were surprised to find a number of circuits that play a role in controlling this behavior," said lead author Keith Murphy, a Scripps graduate student at the time, in the Nov. 22, 2016, press release.

Some of these brain circuits also appeared to be sensitive to the fly's internal clock, as post-meal sleepiness happened less around dusk than at other times of day. It's "fun to speculate" what the biological reason for this might be, William Ja, PhD, associate professor of metabolism and aging at the department of neuroscience on Scripps' Florida campus and researcher on the study, told Health in November 2016.

"Maybe it's so that they can continue foraging and accumulating nutrients before sleep," said Ja. "Or maybe that's a peak time for birds and frogs and other insect eaters to come out, so sleeping at dusk would be especially vulnerable for the flies."

Ja said his lab's discovery could have implications for people, as well: It suggested that food comas are a unique type of sleep, driven by mechanisms independent of other types of shuteye.

"If that's true in humans too, that means there are potentially different targets for us to go after in the future with dietary or drug interventions to help with sleepiness or wakefulness," said Ja in November 2016. As of April 2022, the Ja Lab's research hadn't been applied to humans.

Also in 2016, Ja said the fruit-fly research "provides a starting point for future studies aimed at uncovering the exact genes and circuits that enable meal size, protein, and salt to drive sleep."

Ja and his team hoped to learn more about why, exactly, post-meal naps are necessary—especially since, for animals in nature, sleep is such a vulnerable state.

"For me, the interesting question is, if you believe food coma is a real phenomenon and happens not only in flies, but in mammals and people too, then it must serve some important biological function," said Ja.

"Maybe it's just for good digestion. Or maybe running around with a stomach full of food is just horribly damaging for your gut," continued Ja. "Whatever the function is, do we really want to go around avoiding it?"

That said, if you don't want to find yourself out of commission (or too sleepy to drive) after a meal, Ja said the age-old advice likely held true. According to Ja, it's important to eat in moderation and in smaller bits over a period of time, rather than in large amounts all at once.

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