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The scientific reason you crave junk food after a poor night’s sleep

Runner's World UK logo Runner's World UK 3 days ago Elizabeth Millard
a woman sitting on a bed: Maybe avoid the wafting aromas of your local bake shop if you skimped on sleep the night before. © milanvirijevic - Getty Images Maybe avoid the wafting aromas of your local bake shop if you skimped on sleep the night before.
  • People who are sleep deprived show more activity in the piriform cortex—the part of the brain that receives input from the nose—and eat more calorie-dense foods, a new study published in eLife found.
  • Researchers believe your brain may respond differently to food odors when you are sleep deprived.

There have been numerous studies that connect poor-quality sleep or insomnia with increased desire for not-so-healthy food. Plus, you tend to eat more when you’re chronically sleep deprived, one study found, because your brain craves more energy in the form of calorie-dense food.

Now, a new study is suggesting it’s not only your brain that plays a role: Your nose could also be a real junk food partner in crime.

Published in eLife, the study recruited 29 men and women, aged 18 to 40, and divided them into two groups. One got a normal night’s sleep, then four weeks later, were only allowed to sleep for four hours one night. The experience was reversed for the second group.

After each of the nights, they were offered breakfast as well as a buffet of snacks, and researchers tracked what, and how much, they ate. Before the feast, they were put in an fMRI scanner and presented with a number of different food odors, as well as non-food smells, and had their brain activity tracked.

Each group of participants showed more activity in the piriform cortex—the part of the brain that receives input from the nose—when sleep deprived. They also ate more calorie-dense foods, like doughnuts, chocolate chip cookies, and potato chips, after their short-sleep nights.

“Previous research has shown that sleep deprivation leads to changes in the type of food people eat, and that chronic lack of sleep is linked to obesity,” said senior author Thorsten Kahnt, Ph.D., assistant professor of neurology at Northwestern University Feinberg School of Medicine. “The key finding from our study is that this relationship, at least in part, can be explained by changes in how the brain responds to food odors when we’re sleep deprived.”

It’s possible that it may be related to the endocannabinoid system, which is responsible for regulating the way other systems work in the body. It does this through a series of neurotransmitters and receptors located throughout the body, affecting an array of cognitive and physiological processes, from lung function, pain modulation, and immune response to how your piriform cortex reacts to certain aromas.

“Certain endocannabinoid compounds are enhanced when people are sleep deprived,” Kahnt said. “Our study shows that this increase is related to both changes in food intake and how the brain processes odors when you don’t get enough sleep.”

The study does have limitations, especially its small sample size and brief study period. After all, the subjects had only one night of shortened sleep.

But Kahnt said that the wealth of research connecting sleep deprivation and poor food choices should be enough to sway anyone to pay attention to their sleep habits. And, he added, it wouldn’t be a bad idea to avoid passing the local doughnut shop in the morning if you haven’t gotten much shut-eye the night before.

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