Combined diet and physical activity effects on health-related outcomes in people with overweight or obesity: an overview of systematic reviews.

Background: This overview synthesized evidence from systematic reviews (SRs) of combined physical activity (PA) and diet interventions versus diet-only or PA-only approaches on obesity-related anthropometric, cardiometabolic, and physical fitness outcomes, and identified program features linked to better effects. Methods: We conducted an Overview of SRs following Cochrane guidance and PRIOR standards. Five databases were searched until June 13, 2024, and Google Scholar was updated on January 25, 2025. Eligible SRs synthesized randomized controlled trials of combined PA and diet interventions in people with overweight or obesity. We extracted key intervention characteristics, outcomes, and meta-analytic estimates where available. Methodological quality was assessed with AMSTAR 2, and overlap was quantified using the corrected covered area (CCA). Results: Thirty-two SRs (19 meta-analyses) met inclusion criteria. In adults, combined PA and diet interventions generally outperformed single-component comparators for reducing weight, BMI, waist circumference, and fat mass, and improving cardiorespiratory fitness. More favorable and sustained effects were most often reported in programs lasting ≥6-12 months with frequent, structured contact and supervised, resistance-inclusive exercise. In children and adolescents, face-to-face and family-engaged programs produced the most consistent improvements in BMI/BMI-z, but effects often attenuated 6-12 months after program end without maintenance. In older adults, combined programs reduce fat mass while preserving lean mass, strength, and function. Across diverse settings (including type 2 diabetes, workplaces, and digital delivery), combined interventions improved glucose control, insulin resistance, lipids, and inflammation, and some benefits occurred even without additional weight loss. Long-term lifestyle programs reduced incident type 2 diabetes by about half. Review quality varied (31% high; 69% low/critically low) and overlap between SRs was minimal (CCA 0.0-0.6%). Conclusion: Combined PA and diet interventions tended to outperform diet-only and PA-only approaches. The most consistent and durable benefits were linked to longer duration, higher contact, supervision, resistance training, and family engagement in youth, underscoring maintenance planning. These findings support prioritizing structured lifestyle programs, including scalable hybrid/digital delivery models, while interpreting effects cautiously given the predominance of low-quality SRs. Future research should improve rigor, standardize outcomes, report intervention dose and behavior-change methods, include longer follow-up, and improve representation of underserved groups.