Resistance training as a key strategy for high-quality weight loss in men and women

Background: Preserving fat-free mass (FFM) during weight loss is critical for preventing sarcopenia and maintaining metabolic health. This study examined the effects of resistance training (RT), aerobic exercise (AR), and no exercise (NO) on body composition during a calorie-restricted diet. Methods: This retrospective cohort study included 304 adults (183 men, 121 women; aged 20–74 years; BMI: 18.5–45 kg/m²) who followed a hypocaloric diet and self-selected RT, AR, or NO. The diet was designed to provide an individualized energy deficit of approximately 500 kcal/day, calculated relative to each participant’s measured resting metabolic rate (RMR) and total estimated daily energy expenditure. Body composition was assessed using dual-energy X-ray absorptiometry (DXA), and abdominal circumference (ABC) was measured as a marker of central obesity. Results: Mean follow-up was 5.1 months ± 0.42 months. In men, total weight loss was similar across groups (NO: − 8.5 kg ± 3.2 kg; AR: − 9.0 kg ± 4.2 kg; RT: − 7.7 kg ± 4.2 kg). However, RT produced the greatest reduction in fat mass (RT: − 8.9 kg ± 4.1 kg; AR: − 7.8 kg ± 3.2 kg; NO: − 5.8 kg ± 2.5 kg) and was the only modality associated with an increase in fat-free mass (RT: + 0.8 kg ± 5.0 kg vs. AR: − 1.1 kg ± 2.0 kg and NO: − 2.8 kg ± 1.4 kg). ABC declined in all groups, with larger reductions in RT (− 9.0 cm ± 3.7 cm) and AR (− 8.0 cm ± 3.2 cm) compared with NO (− 6.1 cm ± 2.4 cm). Among women, weight loss was also comparable between groups (NO: − 7.13 kg ± 3.27 kg; AR: − 6.43 kg ± 3.53 kg; RT: − 5.42 kg ± 3.76 kg). RT produced the greatest fat-mass reduction (RT: − 6.36 kg ± 3.82 kg; NO: − 5.47 kg ± 2.64 kg; AR: − 4.10 kg ± 3.17 kg) and was the only modality that increased fat-free mass (RT: + 0.90 kg ± 1.24 kg). Both NO (− 2.94 kg ± 1.40 kg) and AR (− 0.37 kg ± 1.45 kg) experienced FFM loss. The fat mass (FM)-to-weight loss ratio was lowest in the NO group (0.7 ± 0.2), higher in AR (0.86 ± 0.2), and highest in RT (1.1 ± 0.7; p = 0.0002 vs. NO, p = 0.0051 vs. AR). ABC reduction correlated strongly with FM loss (r = 0.84; p = 0.0001), highlighting its utility as a marker of high-quality weight loss. Conclusion: RT enhances weight-loss quality by maximizing FM reduction while preserving or increasing FFM. Incorporating RT into weight-loss programs may improve long-term weight maintenance and mitigate FFM loss.