Severely obese men and women (body mass index ≥ 35 ≤ 55 kg/m2; Mage =44.8 years, SD=9.3) were randomly assigned to a 6-month physical activity support treatment paired with either nutrition education (n = 83) or cognitive-behavioral nutrition (n=82) methods for weight loss. Both groups had significant improvements in physical activity, fatigue, self-regulation for eating, and fruit and vegetable intake. Compared to those in the nutrition education group, participants in the behavioral group demonstrated greater overall increases in fruit and vegetable intake and physical activity. These group differences were associated with changes that occurred after Month 3. Increased physical activity predicted reduced fatigue, β =-.19, p = .01. A reciprocal relationship between the mediators of that relationship, which were changes in self-regulation and fruit and vegetable intake, was identified. There was significantly greater weight loss over six months in the behavioral nutrition group when contrasted with the nutrition education group. Self-regulation for eating and fruit and vegetable intake were significant predictors of weight loss over both three and six months. Findings enabled a better understanding of psychosocial effects on temporal aspects of weight loss and may lead to more effective behavioral treatments for weight loss.