Is our nose to blame for junk food cravings after bad sleep?

Is our nose to blame for junk food cravings after bad sleep?
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People who are sleep deprived tend to reach for doughnuts, fries and pizza – but why do we do this?

A new Northwestern Medicine study, published in eLife, has figured out why you crave more calorie-dense, high-fat junk foods after a sleepless night – and how to help thwart those unhealthy cravings.

Blame it on your nose – or, in other words, your olfactory system – which is affected in two ways by sleep deprivation, according to the study.

First, the system goes into hyperdrive, sharpening the food odours for the brain so it can better differentiate between food and non-food odours.

But then there is a breakdown in the communication with other brain areas that receive food signals. And with that, decisions about what to eat change.

Sleep deprived people chose junk food

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

“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.”

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.

Kahnt said: “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.

“What makes our brain respond differently that makes us eat differently?”

He and colleagues investigated that question in a two-part experiment with 29 men and women, ages 18 to 40. Study participants were divided into two groups. One got 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 night (good sleep and deprived sleep), scientists served participants a controlled menu for breakfast, lunch and dinner, but then also offered them a buffet of snacks. Scientists measured how much and what they ate.

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

Endocannabinoids

Researchers also measured the participants’ blood levels 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 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.

Kahnt said: “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 6am flight.”

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