Struggling to maintain a healthy body weight? Changing your sleep habits may actually be necessary along with changing your diet, according to new research from the American Thoracic Society.

To determine how sleep affects body weight, researchers evaluated a group of nurses in the Cardiac Health Project at Walter Reed Army Medical Center by observing their sleep habits and categorizing them as either short sleepers—getting fewer than the recommended 8 hours a night—or long sleepers. The results? Short sleepers had an average body mass index (BMI) of 28.3—classified as overweight by BMI measures. Long sleepers, on the other hand, had an average BMI of 24.5, which was safely within the healthy weight range.

“Short sleepers also had lower sleep efficiency, experienced as greater difficulty getting to sleep and staying asleep," says lead investigator Arn Eliasson, MD. Surprisingly, Dr. Eliasson says, the overweight nurses in the study were more active than their normal weight counterparts, taking significantly more steps each day: 14,000 compared with 11,300, a nearly 25% difference. The overweight nurses also expended nearly 1,000 more calories a day—a difference of 3,064 versus 2,080 burned by average weight nurses.

Those additional energy expenditures, however, didn’t manifest in reduced weight. Dr. Eliasson speculates that not getting adequate sleep each night disrupts natural hormonal balances, including reducing the satiety hormone leptin, causing the overweight nurses to crave and eat more foods, resulting in weight gain.

Some of that extra activity, he says, was directly related to high levels of perceived stress, which also made the short sleepers feel less organized, “meaning they would have to make more trips and take more steps to accomplish the same tasks. This might add to their stress and encourage other unhealthy behaviors like stress eating," Dr. Eliasson says.