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Scientists have figured out why you keep craving junk food after a night out

A recent study by researchers from Cologne University in Germany found that there is a relationship between lack of sleep and a craving for junk food.

So far, epidemiological studies have suggested there is a link between reduced nocturnal sleep and obesity, but the precise hormonal factors are still not fully known.

This study, published last week in the Journal of Neuroscience, found that participants with sleep deprivation were more willing to overspend on food items than those with a good night’s sleep.

The study was based on a group of 32 healthy men of normal weight between 19 and 33 years old.

“Sleep loss is associated with increased obesity risk, as demonstrated by correlations between sleep duration and change in body mass index or body fat percentage,” says Julia S. Rihm, one of the authors of the study from the Department for Systems Neuroscience, University Medical Center Hamburg-Eppendorf.

“We found ghrelin concentrations were increased after sleep deprivation compared with habitual sleep.”

Ghrelin is dubbed the “hunger hormone” as one of its functions is stimulating appetite and preparing our body for food intake. When our stomach is empty, ghrelin is secreted.

It acts on our hypothalamic brain cells to increase hunger, raising the level of our gastric acid secretion and gastrointestinal motility. When we’re full, ghrelin secretion stops.

The experiment started with giving participants an evening meal of pasta, meat prepared in mushroom sauce and strawberry yogurt.

Then the volunteers were split into two groups: some were sent home wearing a sleep-tracking device, while others stayed at the lab where they were kept awake all night.

All of them were analysed the next morning. Their hunger and appetite were rated, and they underwent a series of tests to determine their blood sugar levels, as well as the levels of certain hormones linked to appetite and stress.

Afterwards, the volunteers took part in a game. They were presented with a series of images – from snacks like chocolate bars to mundane items like university supplies and merchandise.

Members of the group were asked how much they would be willing to pay for the items from nothing to €3 (up to around A$5). As they answered, their brain activity was monitored via functional magnetic resonance imaging.

A week later the experiment was repeated but the roles were switched. Those who stayed awake in the lab previously were sent home, and vice versa.

Researchers found that after periods of sleep deprivation, participants were willing to pay more money for their junk food.

“Despite similar hunger ratings due to fasting in both conditions, participants were willing to spend more money on food items only after sleep deprivation,” the researchers state.

“Furthermore, MRI data paralleled this behavioural finding – revealing how a food reward-specific up-regulation of hypothalamic valuation signals and amygdala-hypothalamic coupling after a single night of sleep deprivation.”

These findings do align with life experience. I mean, after a whole night studying, partying or working, an apple or a bowl of granola isn’t quite the first thing to pop up in our minds when it comes to food, is it?

About the author

Filmmaker. 3D artist. Procrastination guru. I spend most of my time doing VFX work for my upcoming film Servicios Públicos, a sci-fi dystopia about robots, overpopulated cities and tyrant states. @iampineros

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