June 10/New York/HealthDay News -- Unhealthy foods, such as sweets and chips, are more appealing to people who have not had enough sleep, new research suggests. 

When researchers examined the areas of the brain that were most active when people were looking at healthy or unhealthy foods, they found the reward centers of the brain were activated when sleep-deprived study volunteers saw pictures of unhealthy foods.

"We found regions associated with reward and motivation -- those that are involved with addiction and pleasure-seeking behaviors -- were more strongly activated in the short-sleep phase," said Marie-Pierre St-Onge, a research associate at St. Luke's Roosevelt Hospital Center and an assistant professor at Columbia University's Institute of Human Nutrition in New York City.

A second small study did not find a large difference in the activation of the brain's reward centers in people who were tired. The researchers from the University of California, Berkeley did, however, find significantly impaired activity in an area in the frontal lobe of the brain. This area of the brain helps control behavior and make complex choices. When people were sleep-deprived and then presented pictures of unhealthy foods, this area of the brain did not respond well, which would make choosing healthy foods more difficult.

The study included 16 healthy young adults who underwent functional magnetic resonance imaging (fMRI) once after a full night of sleep and then again after 24 hours of sleep deprivation. They were asked to rate their desire for 80 different foods during each test.

St-Onge's study included 25 normal-weight men and women who underwent fMRI after five nights of restricted sleep (four hours a night) and then again after five nights of being allowed to sleep for nine hours.

While they were in the fMRI scanner, they were shown pictures of healthy foods, such as fruits, vegetables and oatmeal; unhealthy foods, such as candy or pepperoni pizza; and nonfood items, such as office supplies.

They found that unhealthy foods activated areas of the brain considered reward centers only in people whose sleep was restricted. When the same people were allowed to rest a full night, they had no such activation in the brain's reward center when they saw the unhealthy foods.

"I think it's related to cognitive control," St-Onge explained. "Your guard is somewhat down when you're tired and sleep deprived. Even though you know you probably shouldn't eat certain foods, when you're tired you might just decide to go for it."

Because this study was presented at a medical meeting, the data and conclusions should be viewed as preliminary until published in a peer-reviewed journal.

 From the June 11, 2012, Prepared Foods’ Daily News