Two new studies that scanned the brains of people who have been sleep deprived have revealed their brains react differently when presented with choices of healthy and unhealthy food compared to those who have had adequate sleep.
The research showed that key areas of the brain related to reward were activated while activity in regions that control behaviour were inhibited.
The findings may help to explain the link between sleep deprivation and obesity.
Dr Marie-Pierre St-Onge, from Columbia University in New York who led one of the studies, said: “The results suggest that, under restricted sleep, individuals will find unhealthy foods highly salient and rewarding, which may lead to greater consumption of those foods.”
In her study 25 men and women of normal weight were asked to look at images of healthy and unhealthy food while in an fMRI scanner after five nights where their sleep was either restricted to just four hours or they were allowed to get up to nine hours.
In those who had less sleep, the reward centres of the brain were more active when shown pictures of unhealthy food compared to those who had more sleep.
When they were shown pictures of healthy food this area of the brain did not activate.
Dr St-Onge, who is presenting the research at the annual conference of the American Academy of Sleep Medicine and the Sleep Research Society, added: “This may suggest greater propensity to succumb to unhealthy foods when one is sleep restricted.
“Indeed, food intake data from this same study showed participants ate more overall and consumed more fat after a period of sleep restriction compared to regular sleep.”
The second study, also being presented at the conference, looked at 23 healthy adults after a normal nights sleep and a night where their sleep had been restricted.
After each night, the participants were asked to rate how much they wanted food items shown to them while inside a fMRI scanner.
Stephanie Greer, who conducted the work at the sleep and neuroimaging laboratory at the University of California, Berkeley, said sleep deprivation impaired the activity in the frontal lobe of the participants brains – an area critical for behaviour control and making choices.
She said they failed to see any activity in areas of the brain associated with reward in this study.
She said: “It seems to be about he regions higher up in the brain, specifically within the frontal lobe, failing to integrate all the different signals that help us normally make wise choices about the food we eat.”
She added that if people cannot make the right choices about what food to eat after suffering from poor sleep, it may explain why other studies have found a lack of sleep is risk factor for obesity.