Body composition and physical fitness in transgender versus cisgender individuals: a systematic review with meta-analysis

OBJECTIVE: To compare body composition and physical fitness between transgender and cisgender individuals. DESIGN: Systematic review with meta-analysis. DATA SOURCES: PubMed, Web of Science, Embase and SportDiscus. ELIGIBILITY CRITERIA: Inclusion criteria comprised studies of transgender individuals comparing body composition or physical fitness pre-to-post gender-affirming hormone therapy (GAHT) or versus cisgender controls. RESULTS: 52 studies (n=6485) were included. Transgender women had similar relative fat mass (standardised mean difference (SMD) -0.33, 95% CI -0.72 to 0.05, Grading of Recommendations Assessment, Development and Evaluation (GRADE): very low), relative lean mass (SMD 0.19, 95% CI -0.14 to 0.53, GRADE: low), upper-body strength (SMD 0.54, 95% CI -0.95 to 2.02, GRADE: very low), lower-body strength (SMD 0.05, 95% CI -1.31 to 1.40, GRADE: very low) and maximal oxygen consumption (SMD -0.28, 95% CI -0.81 to 0.25, GRADE: very low) in comparison to cisgender women. Transgender men exhibited higher relative fat mass (SMD 0.96, 95% CI 0.28 to 1.64, GRADE: moderate), lower relative lean mass (SMD -6.42, 95% CI -12.26 to -0.58, GRADE: moderate) and lower upper-body strength (SMD -1.46, 95% CI -2.52 to -0.40, GRADE: moderate) than cisgender men. In transgender women, GAHT was associated with increased fat mass and reduced lean mass and upper-body strength over 1-3 years. Transgender men demonstrated reduced fat mass and increased lean mass and strength following GAHT. CONCLUSION: While transgender women exhibited higher lean mass than cisgender women, their physical fitness was comparable. Current evidence is mostly low certainty and has heterogenous quality but does not support theories of inherent athletic advantages for transgender women over cisgender. PROSPERO REGISTRATION NUMBER: CRD42024562210.