Body recomposition in adults: mechanisms, modulators, and practical algorithms for simultaneous skeletal muscle mass gain and fat mass loss

BACKGROUND: Body recomposition is the concurrent increase in fat-free mass (FFM) or skeletal muscle mass and decrease in fat mass (FM) within the same intervention period. Although hypertrophy is commonly pursued in energy surplus and FM loss in energy deficit, controlled trials indicate that recomposition can occur when progressive resistance training (PRT), adequate protein intake, and an appropriate energy prescription are combined. METHODS: We conducted a structured narrative review of randomised trials, meta-analyses, and selected mechanistic studies in adults, with emphasis on FFM, FM, strength, and performance outcomes. Device heterogeneity was considered when interpreting evidence, with greatest weight placed on four-compartment and dual-energy X-ray absorptiometry (DXA) outcomes. RESULTS: PRT combined with higher protein intake, typically ~1.6-2.4 g/kg/day and higher relative intakes during energy restriction or leanness, is the most consistent strategy for recomposition. Effects are largest in untrained individuals and those with higher adiposity, smaller in trained or lean athletes, and still feasible in older adults when anabolic resistance is addressed with supervised PRT and sufficient protein. Moderate deficits, carbohydrate allocation around key sessions, sleep, and recovery support FFM retention or accretion while facilitating FM loss. Practical applications: Programmes should pair progressive overload with protein-centred diets, modest energy deficits, and periodic monitoring of body composition and performance. CONCLUSIONS: Body recomposition is feasible but context-dependent; expected changes are generally modest in trained or lean populations and require individualised adjustment.