Body mass index and body composition changes in transgender people undergoing gender-affirming hormone therapy: a systematic review and meta-analysis.

Gender-affirming hormone therapy (GAHT) uses sex steroid hormones to induce desired physical changes, improving the quality of life of transgender individuals. While generally considered safe, its effects on body composition and adipose tissue remain a topic of debate. The aim of this review was to verify whether GAHT is associated with weight gain and body composition in transgender individuals. This is a systematic review with meta-analysis (April-September 2022, updated March 2025) following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, including cohort, case‒control, and clinical trial studies from four databases. The outcomes analyzed included body mass index (BMI), body fat (BF), lean mass (LM), and waist circumference (WC). Among the 1,896 identified studies, 29 were included in the systematic review, and 28 were included in the meta-analysis. GAHT increased BMI in assigned male at birth (AMAB) individuals (0.55 kg/m², 95% CI: 0.14-0.97) and assigned female at birth (AFAB) individuals (0.92 kg/m², 95% CI: 0.55-1.29). The AMAB participants presented a reduction in LM (-1.81 kg, 95% CI: -3.15, -0.47) and an increase in BF (4.27 kg, 95% CI: 3.15-5.39), whereas the AFAB individuals presented an increase in LM (4.98 kg, 95% CI: 4.06-5.91) and a decrease in BF (-2.13 kg, 95% CI: -3.52, -0.75). No significant changes in WC were observed in either group. According to the GRADE assessment, the certainty of evidence was moderate for BMI and low to very low for changes in waist circumference, lean mass, and fat mass. GAHT is associated with increased BMI and body composition changes. These alterations align with the expected outcomes for transgender individuals and do not appear to be directly linked to cardiovascular risks.