We all know getting a good night's sleep is important. Your body repairs and renews itself while you sleep, so it's key for good skin and maintaining a clean bill of health.

But did you know that if you don't sleep well you're more likely to crave junk food?

Last year, researchers at Feinberg School of Medicine, Northwestern University in Chicago presented their results of a study looking into the effects of sleep deprivation upon high-calorific food consumption at the Cognitive Neuroscience Society's annual meeting in San Francisco, reports Science News.

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Volunteers of the study were allocated different amounts of sleep - eight hours or four hours - and then their reaction to smells of high-calorific foods were tested.

Participants slept for both lengths of time, separated by a week of normal sleep. On the day after they either had full or partial sleep, participants rated the pleasantness and intensity of sweet and savoury high-calorific food smells such as crisps and cinnamon rolls. They were then asked to rate the smell of non-foods like fir trees.

Researchers found that those who were sleep-deprived had 'specifically enhanced' brain activity to the food smells compared to when they had a good night's sleep.

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The experiment follows a similar study in 2013 from University College Berkeley in which researchers hooked 23 healthy young adults to an MRI scan to study the brain after a normal night's sleep and after a sleepless night.

Both times the participants were shown pictures of healthy foods like apples and carrots as well as junk food like doughnuts and pizza. They were told they would receive the food they craved most after the scan.

When sleep-deprived, volunteers craved unhealthy foods more with the scan finding an impairment in the area of the brain that governs decision-making and increased activity in the area that governs rewards.

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Stephanie Greer, the study's lead author says: 'The results shed light on how the brain becomes impaired by sleep deprivation, leading to the selection of more unhealthy foods, and, ultimately, higher rates of obesity.

'The findings indicate that getting enough sleep is one factor that can help promote weight control by priming the brain mechanisms governing appropriate food choices.'

In 2012, researchers from the University of Chicago Clinical Resource Centre also discovered that too many late nights affect how your body responds to insulin — a hormone that regulates your appetite and metabolism.

In particular, after healthy men and women slept only 4.5 hours of sleep a night for four days, their fat cells became 30 per cent less sensitive to insulin.

So, if you want to stop yourself reaching for that chocolate-coated snack before midday day, perhaps try getting a few 'Zzzs' at night.