Find out why you crave junk food after a sleepless night and what you can do to thwart those unhealthy cravings

When sleep-deprived, you probably find yourself craving chips, chocolate and pizza.

Now a new Northwestern Medicine study has figured out why you crave more calorie-dense, high-fat foods after a sleepless night – and how to help thwart those unhealthy choices.

Being led by your nose

Blame it on your nose – or olfactory system – which is affected in two ways by sleep deprivation.

First, the nose goes into hyperdrive, sharpening the food odours for the brain so it can better differentiate between food and non-food odours. Secondly, there is a breakdown in the communication with other brain areas that receive food signals. And without that information, decisions about what to eat will change.

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When you’re sleep-deprived, these brain areas may not be getting enough information, and you’re overcompensating by choosing food with a richer energy signal,” says senior author Thorsten Kahnt, assistant professor of neurology at Northwestern University Feinberg School of Medicine.

“But it may also be that these other areas fail to keep tabs on the sharpened signals in the olfactory cortex. That could also lead to choosing doughnuts and potato chips,” Kahnt adds.

Past research shows sleep deprivation increases certain endocannabinoids, which are naturally produced by the body and are important for feeding behaviour and how the brain responds to odours, including food smells.

“We put all this together and asked if changes in food intake after sleep deprivation are related to how the brain responds to food odours, and whether this is due to changes in endocannabinoids,” says Kahnt. “What makes our brain respond differently that makes us eat differently?”

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The study

He and his colleagues investigated that question in a two-part experiment with 29 men and women, aged 18 to 40. Study participants were divided into two groups. One group had a normal night’s sleep, then four weeks later, were only allowed to sleep for four hours. The experience was reversed for the second group.

The day after each ‘good sleep’ and ‘deprived sleep’ night, the participants were served a controlled menu for breakfast, lunch and dinner, and offered them a buffet of snacks. Scientists measured how much and what they ate.

“We found participants changed their food choices,” says Kahnt. “After being sleep deprived, they ate food with higher energy density (more calories per gram) like doughnuts, chocolate chip cookies and potato chips.”

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The science

Researchers measured the participants’ blood level of two endocannabinoid compounds – 2AG and 2OG. One of the compounds, 2-OG, was elevated after the night of sleep deprivation and this increase was related to changes in food selection.

In addition, scientists put subjects in an fMRI scanner, before the buffet. They then presented them with a number of different food odours and non-food control odours while they observed the piriform cortex, the first cortical brain region that receives input from the nose.

They observed that activity in the piriform cortex differed more between food and non-food odours when subjects were sleep deprived.

The piriform cortex normally sends information to another brain area, the insular cortex. The insula receives signals that are important for food intake, like smell and taste, and how much food is in the stomach.

But the insula of a sleep-deprived subject showed reduced connectivity (a measure of communication between two brain regions) with the piriform cortex. And the degree of this reduction was related to the increase in 2-OG and how much the subjects changed their food choices when sleep deprived.

“When the piriform cortex does not properly communicate with the insula, then people start eating more energy-dense food,” Thorsten said.

The solution

Other than getting more sleep, it may help to pay closer attention to how our nose sways our food choices.

“Our findings suggest that sleep deprivation makes our brain more susceptible to enticing food smells, so maybe it might be worth taking a detour to avoid your local doughnut shop next time you catch a 6 a.m. flight,” says Kahnt.

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Source: Northwestern University via www.sciencedaily.com

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