Summary: Lack of sleep ramps up the sense of smell for food while disrupting communication between smell-processing areas and regions that guide eating decisions, which shifts people toward higher-calorie choices.
Source: Northwestern University
Overview: When you’re short on sleep, you may find yourself reaching for doughnuts, fries and pizza. A Northwestern Medicine study explains why sleepless nights increase cravings for calorie-dense, high-fat foods, and points to how those urges might be reduced.
The study identifies two key effects of sleep deprivation on the olfactory system. First, the brain’s primary smell-processing region becomes more sensitive to food odors, improving its ability to tell food smells apart from non-food smells. Second, connections between this olfactory region and other brain areas that integrate feeding signals weaken, altering decision-making about what to eat.
“Sleep loss appears to sharpen smell signals while impairing how other brain regions read those signals,” said Thorsten Kahnt, assistant professor of neurology at Northwestern University Feinberg School of Medicine and senior author of the study. “That combination may push people to seek out foods that provide a stronger energy signal—foods like doughnuts or potato chips.”
The findings were published Oct. 8 in the journal eLife.
Previous research has shown that sleep deprivation elevates certain endocannabinoids—naturally produced compounds that influence feeding behavior and the brain’s response to odors. Building on that work, this study asked whether sleep-related changes in food intake are tied to how the brain processes food odors and whether endocannabinoids play a mediating role.
The researchers tested 29 healthy adults, ages 18 to 40, in a within-subjects design. Participants completed two conditions: a normal night’s sleep and a restricted night with only four hours of sleep, with the order counterbalanced across participants and separated by four weeks. The day after each sleep condition, participants received controlled meals for breakfast, lunch and dinner and, later, a snack buffet where they could freely choose and eat items. Investigators measured both what and how much participants consumed.
Results showed a clear shift in food choice after sleep restriction. Following the short-sleep night, participants favored foods with higher energy density—more calories per gram—such as doughnuts, chocolate chip cookies and potato chips.
Blood tests measured levels of two endocannabinoid compounds, 2-arachidonoylglycerol (2-AG) and 2-oleoylglycerol (2-OG). The study found that 2-OG increased after sleep loss, and the rise in 2-OG correlated with the shift toward energy-dense foods.
Functional MRI scanned participants before the buffet while they were exposed to a series of food and non-food odors. The team focused on the piriform cortex, the cortical region that first receives olfactory input from the nose. Activity in the piriform cortex showed a stronger distinction between food and non-food odors when participants were sleep deprived—consistent with heightened odor encoding.
Under normal conditions the piriform cortex passes olfactory information on to the insular cortex (insula), a region that integrates smell and taste with internal signals such as stomach fullness. In the sleep-deprived state, functional connectivity between the piriform cortex and the insula was reduced. Importantly, the degree of reduced connectivity was related both to the increase in 2-OG and to how much participants altered their food choices after sleep loss.
“When the piriform cortex does not properly communicate with the insula, people tend to choose more energy-dense foods,” Kahnt said.
Practical implications: aside from getting adequate sleep, being aware that acute sleep loss makes smell cues more compelling could help people avoid impulsive, high-calorie choices. For example, steering clear of tempting bakeries or snack aisles after an all-nighter may reduce the likelihood of giving in to energy-dense options.
Funding: This research was supported by the National Center for Advancing Translational Sciences (UL1652 TR001422), the National Heart, Lung, and Blood Institute (T32 HL007909), the National Institute of Diabetes and Digestive and Kidney Diseases (R21 DK118503), and the National Institute on Deafness and Other Communication Disorders (R01655 DC015426), all part of the National Institutes of Health.
Authors and credits: Other Northwestern authors include first author Surabhi Bhutani, James D. Howard, Rachel Reynolds, Phyllis Zee and Jay A. Gottfried.
Source:
Northwestern University
Media Contacts:
Marla Paul – Northwestern University
Image Source:
The image is in the public domain.
Original Research (open access):
“Olfactory connectivity mediates sleep-dependent food choices in humans.” Surabhi Bhutani et al., eLife. DOI: 10.7554/eLife.49053.
Abstract
Olfactory connectivity mediates sleep-dependent food choices in humans
Sleep deprivation shifts food choices toward energy-dense options. This study tested whether central olfactory circuits and the endocannabinoid system (ECS) mediate that effect. Using a partial sleep-deprivation protocol, pattern-based olfactory neuroimaging, and ad libitum food intake, the researchers found that sleep restriction increased levels of the ECS compound 2-oleoylglycerol (2-OG), enhanced encoding of food odors in the piriform cortex, and shifted choices toward higher-energy foods. Critically, changes in 2-OG and food choice were mediated by odor-evoked connectivity between the piriform cortex and the insula, a region that integrates feeding-related signals. These findings outline a neurobiological pathway by which state-dependent changes in the ECS may modulate chemosensory processing to influence food selection.