Abstract
Objective: Test whether the efficacy of Project Health, an obesity/eating disorder prevention program, is improved by delivering it in single-sex groups and adding food response inhibition and attention training. Method: High-risk young adults (N = 261; M age = 19.3, 74% female) were randomized to (1) single-sex or (2) mixed-sex groups that completed food response inhibition and attention training or (3) single-sex or (4) mixed-sex groups that completed sham training with nonfood images in a 2 × 2 factorial design. Results: There was a significant sex-composition by training-type by time interaction; participants who completed single- or mixed-sex Project Health groups plus food response and attention training showed significant reductions in body fat over a 2-year follow-up, though this effect was more rapid and persistent in single-sex groups, whereas those who completed single- or mixed-sex Project Health groups plus sham training did not show body fat change. However, there were no differences in overweight/obesity onset over the follow-up. The manipulated factors did not affect eating disorder symptoms or eating disorder onset, but there was a significant reduction in symptoms across the conditions (within-condition d = -0.58), converging with prior evidence that Project Health produced larger reductions in symptoms (within-condition d = -0.48) than educational control participants. Average eating disorder onset over the 2-year follow-up (6.4%) was similar to that observed in Project Health in a past trial (4.5%). Conclusions: Given that Project Health significantly reduced future onset of overweight/obesity in a prior trial and the present trial found that body fat loss effects were significantly greater when implemented in single-sex groups and paired with food response and attention training, there might be value in broadly implementing this combined intervention.