August 6/Berkeley, Calif./UC Berkeley -- Science has been pretty strong on connecting sleep deprivation to weight gain. Now a new study from UC Berkeley shows one reason might lie in the brain and how it is affected by sleep deprivation.

While the study was small -- 23 people -- it is intriguing. The recruits were monitored for two individual nights, a week apart. On one night, they got a normal night’s sleep (8.2 hours on average). On the other night, they were not allowed to sleep at all. After they had not slept, the study participants showed a much stronger preference for high-calorie foods, such as pizza and doughnuts, over more healthful choices like strawberries and carrots.

In addition, researchers, led by Matthew Walker, a UC Berkeley psychology professor, measured areas of the brain using functional magnetic resonance imaging. The preference for high-calorie foods among the sleep-deprived matched with greater activity in an area of the brain called the amygdala, which the authors say has been “strongly implicated in governing the motivation to eat.” At the same time, those who were sleep-deprived had “significantly reduced activity” in three areas of the brain that have to deal with decision-making.

The sleep-deprived subjects wanted higher-calorie foods and had impaired rational decision-making to overcome those urges.

“This combination of altered brain activity and decision-making may help explain why people who sleep less also tend to be overweight or obese,” said Walker in a release.

In the study, published in the journal Nature Communications, researchers measured the desire for junk food by showing participants pictures of foods and having them rank their desire for each of the 80 foods they were shown. The difference in total calories of foods wanted in the sleep-deprived state vs. the rested state was about 600 calories.

The participants were asked to rate their hunger, and there was no difference between the two sessions, “suggesting that the condition of sleep loss, rather than metabolic need or hunger, acts as a primary factor influencing the observed changes,” the authors write.

Still, more research is needed. Walker and his colleagues point to areas for further investigation. First, instead of showing subjects pictures of food, study participants could be allowed to eat what they want to see if high-calorie food would “normalize the observed brain responses under sleep deprivation,” they write. In addition, the 23 subjects in this study were young, healthy and lean. “An important future challenge will be to examine whether similar alterations caused by sleep deprivation are expressed across a broader age and body mass range.”