Effects of rehydration and nutritional recovery strategies after rapid weight loss on body mass recovery, hydration status, and performance in combat sports athletes: a systematic review and meta-analysis

Background Rapid Weight Loss (RWL) is common in weight-category combat sports, but the extent to which post-weigh-in feeding and rehydration restore body mass, hydration, and exercise performance remains uncertain. Objective To quantify post-weigh-in body-mass regain and hydration status and to evaluate nutritional and rehydration strategies and subsequent exercise performance in combat-sport athletes. Methods This review followed PRISMA 2020 and was registered in PROSPERO (CRD420261438676). PubMed, SPORTDiscus, Embase, and Web of Science were searched from inception to July 2026. English-language human studies involving RWL or weight making followed by recovery were eligible. Comparable continuous outcomes were pooled using random-effects models with modified Hartung-Knapp confidence intervals; heterogeneous strategy and performance outcomes were synthesized using evidence maps and effect-direction methods. Results Forty studies were included in the main post-weigh-in recovery review. Pooled post-weigh-in body-mass regain was 6.23% of body mass (95% CI 3.74–8.71; k = 11; n = 1504; I 2 = 99.2%) and 3.71 kg (95% CI 2.45–4.96; k = 12; n = 1451; I 2 = 98.9%). In five matched cohorts with paired pre-weigh-in and follow-up measurements, RWL was 8.33% of body mass (95% CI 6.17–10.49; n = 179), followed by a median regain of 106.5% of the preceding loss (range 63.2–154.1%). At official weigh-in, pooled mean urine specific gravity (USG) was 1.029 (95% CI 1.025–1.033; k = 3; n = 58; I 2 = 92.7%). Urine osmolality was reported in seven studies and plasma osmolality in four, but these data were not sufficiently comparable for pooling. Twenty-three performance records from 12 studies were too heterogeneous for meta-analysis. No specific nutritional or rehydration approach had sufficiently homogeneous comparative evidence for a strategy-effect meta-analysis. Conclusion Combat-sport athletes commonly regain substantial body mass after weigh-in, but body-mass regain should not be interpreted as complete rehydration or restored performance readiness. Current strategy-specific evidence is insufficient to identify a superior recovery protocol; standardized, adequately powered trials using multidimensional recovery outcomes are needed. Systematic review registration identifier: CRD420261438676.