Remember the last time you gorged on the chicken burger for lunch and then just couldn’t keep your eyes open for that afternoon meeting. Why?
Scientists have been wondering since forever that why or how eating heavy meals results in drowsiness. A study on fruit flies, however, offered some potential clues. And surprisingly, the usual suspects- carbohydrates and sugar aren’t the culprits!
To investigate the neurobiological links between eating and sleep, researchers from Bowling Green State University in Ohio and Florida’s Scripps Research Institute used fruit-flies. What came forward was that consuming protein and salt leads to the infamous food coma as our bodies have to work harder to digest them and extract the nutrients.
“In Drosophila, there is a well-documented interaction between sleep and metabolism, whereby flies suppress sleep or increase their activity when starved,"
says William Ja, Ph.D., Associate Professor in the Department of Metabolism and Aging at Scripps Florida.
Ja and his team created the Activity Recording Cafe (ARC) to visually track food consumption by the fly and its movement. Behavior recordings reveal that, after eating a meal, the animals sleep more before returning to a normal state of wakefulness.
To determine which particular nutrients and food types modulate post-meal sleep, the flies were fed with food consisting of protein, salt or sugar. It was observed that only protein and salt affected post-meal sleep. A possible explanation for this could be that protein delays gastric dumping. In other words, protein-rich food, with its surrounding supply of blood, tends to stay in the stomach for a longer time.
So what biological function (if any) do these post-meal naps serve?
As stated in eLife, when genetic tools were employed to turn neurons on and off in the fly’s brain in order to identify the neuronal mechanism by which feeding drives post-meal sleep, it was surprisingly observed that a number of circuits play a role in controlling this behavior.
As per the previous study, the Lkr neuronal system actively signals a behavioral shift during feeding as it plays a role in meal-size regulation. Building on this work, the current study demonstrated that the Lkr system plays a role in post-meal sleep.
Keith Murphy, the first author of the study pointed out:
“A subset of leucokinin receptor (Lkr) neurons was necessary to initiate post-meal sleep in the presence of protein specifically. While we expected that flies defective in protein sensing would experience post-meal sleep in a similar way to those fed only sucrose, we found instead that they had a waking response. Our analysis suggests that ingested protein promotes both sleep and wakefulness and that the wakefulness is counterbalanced by Lkr neuronal activity.”
It was also found that other brain circuits are sensitive to the fruit fly’s internal clock, reducing post-meal sleepiness only around dusk. Taking these results together, the team concluded that post-meal sleepiness can be regulated in a number of different ways in flies and humans alike.
Ja says the fruit-fly research
“provides a starting point for future studies aimed at discovering the exact genes and circuits that enable meal size, protein, and salt to drive sleep.”
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