Group-Based Diet and Physical Activity Weight-Loss Interventions: A Systematic Review and Meta-Analysis of Randomised Controlled Trials

Background: Many weight-loss interventions are delivered in groups but evidence on their effectiveness, and characteristics associated with effectiveness, is limited. We synthesised evidence on (1) design and delivery of group-based weight-loss interventions; (2) effectiveness; and (3) associations between intervention characteristics, change techniques, and effectiveness. Methods: Five online databases were searched to May 2017 for randomised controlled trials (RCTs) of group-based diet and/or physical activity interventions for overweight/obese adults (BMI ≥ 25). Intervention characteristics were synthesised narratively. Mean differences (MD) in weight loss were calculated using a random-effects meta-analysis, and sub-group analyses were conducted to identify moderators of effectiveness. Results: Forty-seven RCTs reporting 60 evaluations of group-based interventions were included. MD in weight loss between intervention and control groups was −3.49 [95% CI −4.15, −2.84], −3.44 [−4.23, −2.85], and −2.56 kg [−3.79, −1.33] at follow-ups closest to 6, 12, and 24 months, respectively. Explicitly targeting weight loss, men-only groups providing feedback and dietary goals were significantly associated with greater effectiveness (p