Scientists discover why we love a snooze after dinner

Fruit flies help scientists to understand why too much food makes us sleepy

Fruit flies that eat too much have helped scientists to understand why we tend to fall asleep after a big meal. Millions of people celebrating Thanksgiving will overindulge on Thursday and then fall into what researchers describe as a "food coma". The traditional heavy meals at Christmas do the same thing.

Although a fruit fly's portion might be a tad small for humans, these insects also fall into a post-dining stupor if they have too much. Researchers at the Scripps Research Institute Florida campus and colleagues from other institutions decided to find out why this happens and what foods in particular might trigger a food coma.

Lead researcher Prof William Ja of the department of metabolism and ageing at Scripps turned for an answer to a key participant in modern science, the fruit fly Drosophila melanogaster, publishing the study results in the online journal, eLife. The team developed a system to measure both the sleep and feeding behaviours of individual fruit flies and then watched what happened after a double helping of favourite foods.

They found the flies typically took a 20- to 40-minute nap right after dining, with the heavy eaters sleeping even longer. The team also discovered that only certain foods triggered this response, with protein-rich foods and salty foods both encouraging a food coma. Unexpectedly, sweet foods did not have this effect, something that might tempt those with a sweet tooth to try one more portion.

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Having shown there is something to this post-prandial food coma effect in the fruit fly, the team believes its work provides a way to study the relationship between food and sleep in the bugs and in humans, according to Prof Ja.

“This behaviour seems conserved across species, so it must be valuable to animals for some reason,” he said. “As sleep is a vulnerable state for animals in nature, it will be interesting to discover why post-meal naps are necessary.”

Dick Ahlstrom

Dick Ahlstrom

Dick Ahlstrom, a contributor to The Irish Times, is the newspaper's former Science Editor.