For many women coping with obesity and depression, new research finds that improving your mood might be the link to losing weight.

The new study, which appeared in a recent issue of the journal General Hospital Psychiatry, cites past surveys that show having a body mass index (BMI) of 30 or more—classified as obese—increases a person's risk of depression by a range of 50 percent to 150 percent.

"I expect that the relationship between depression and physical activity goes in both directions," says lead author Dr. Gregory Simon, of Group Health Research Institute, in Seattle. "Increased physical activity leads to improvement in depression and improvement in depression leads to increased physical activity. We see in our study that they go together, but we can't say which causes which."

Simon and his colleagues evaluated 203 women ages 40 to 65 with an average BMI of 38.3. Participants underwent baseline tests to measure their weight, depression score, physical activity, and food intake.

They placed the women into two treatment groups—one focused on weight loss and the other focused on both weight loss and depression. Both interventions included up to 26 group sessions over 12 months, and researchers followed up on participants at six, 12, and 24 months after enrollment.

The researchers found the most significant changes happened in the first six months and then remained stable afterwards. At six months, among the women who had at least a one-half point decrease on the Hopkins Symptom Checklist depression score, 38 percent lost at least 5 percent of their body weight. This compared with 21 percent of the women who lost the same amount but had no decrease—or an increase—in their depression score.

"Most weight-loss programs do not pay enough attention to screening and treatment of depression," says Dr. Babak Roshanaei-Moghaddam, of the psychiatry and behavioral sciences department at the University of Washington, in Seattle. "This study further underscores the importance of screening for depression in such programs that can potentially lead to both physical and psychological well-being."