UC San Diego

Overweight and obesity result in serious medical, economic, and psychological consequences. A better understanding of factors that lead to successful weight loss treatment is needed, including mediators and moderators of treatment effects. This study investigated the effect of depression on adherence to a dietary and physical activity behavior change intervention in a sample of overweight and obese men and women. The PACEi Men in Motion (n=441) and Women in Balance (n=401) on-line interventions used similar randomized controlled designs with data collected at baseline, 6, and 12 months. Outcomes included BMI, depression, dietary quality, physical activity and sedentary behavior. Adherence scores reflected the percentage of potential intervention activities completed. Moderator and mediator analyses were performed as described by Baron and Kenny (1986) and Kraemer et al. (2002). A mediating relationship among depression, adherence, and outcome was supported for dietary quality in men; no relationship was found for women. In addition, baseline depression in men was related to lower adherence rates, and, in turn, lower adherence rates predicted poorer outcome for BMI, physical activity, sedentary behavior, and dietary quality. For women, adherence was not affected by baseline depression but lower adherence did predict poorer dietary quality outcomes. However, baseline level of depression in women was found to moderate the intervention effect on dietary changes, where women in the intervention group improved their dietary quality more than the control group, with greater improvements seen in the depressed intervention women. Depressed women in the control group had a slight decrease in diet quality. Baseline level of depression was also found to moderate the intervention effect on sedentary behavior for men. Men in the intervention group reduced their sedentary behavior about the same amount, regardless of depression status at baseline, while in the control group, depressed men decreased their sedentary behavior and non-depressed men had a slight increase. This study provided further evidence for the relationship between adherence and outcome. The relationship between depression and adherence was supported only for men. Overall, the study provided evidence that participating in a dietary and physical activity intervention while experiencing depressive symptoms is not harmful, and may be beneficial in some cases. Screening out participants who are similarly depressed due to concern for their ability to participate may not be warranted. Future studies should investigate strategies to promote adherence to weight loss interventions as a method of enhancing outcomes in addition to examining the effects of treating depression either before or concurrently with weight loss interventions