If you’ve ever eaten your weight in mashed potatoes and turkey and then made a beeline for the couch to nap it off, chances are you’ve experienced the condition likely to strike millions this long weekend known as a "food coma."

Until now, little has been known about why this phenomenon actually occurs. 

In a new study published in the journal eLife, scientists observed the sleep patterns of fruit flies after eating. What they discovered was that only certain kinds of food caused the flies to become sleepy, with salt and protein motivating them to rest for a period of up to 40 minutes and sugar having no such effect.

The scientists then observed the flies’ brain activity as they ate, and discovered that protein activated neurons in their receptors for leucokinin (a neurotransmitter that regulates fruit flies’ food intake, and is the equivalent of tachykinin in vertebrates) and caused them to go to sleep.

When the scientists genetically silenced the flies’ leucokinin receptor neurons, they no longer became fatigued after eating proteins.

“By turning on and off neurons in the fly brain, we identified several circuits dedicated to controlling postprandial sleep,” said study co-author Keith Murphy in a statement.

The scientists also noted that salt consumption has been known to impact oxytocin signaling, which helps regulate sleep, and could thus also contribute to the food coma phenomenon.

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The scientists added that sleep might help digestion. However, more research is needed into food comas as a whole to determine how they might benefit animals of all kinds - in the wild or on Grandma's sofa bed after a particularly sumptuous Thanksgiving feast. 

h/t IFLScience.