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

GAHT increased BMI in both AMAB and AFAB transgender individuals.

• AMAB individuals (transgender women) experienced a BMI increase of 0.55 kg/m², 95% CI: 0.14–0.97.
• AFAB individuals (transgender men) experienced a larger BMI increase of 0.92 kg/m², 95% CI: 0.55–1.29.
• GRADE certainty of evidence was moderate for BMI outcomes.
• 28 studies were included in the meta-analysis out of 29 in the systematic review, identified from 1,896 initial studies.

AMAB individuals undergoing GAHT experienced a reduction in lean mass and an increase in body fat.

• Lean mass decreased by 1.81 kg (95% CI: -3.15, -0.47).
• Body fat increased by 4.27 kg (95% CI: 3.15–5.39).
• GRADE certainty of evidence was low to very low for lean mass and fat mass changes.
• These changes reflect feminizing effects expected from estrogen-based hormone therapy.

AFAB individuals undergoing GAHT experienced an increase in lean mass and a decrease in body fat.

• Lean mass increased by 4.98 kg (95% CI: 4.06–5.91).
• Body fat decreased by 2.13 kg (95% CI: -3.52, -0.75).
• GRADE certainty of evidence was low to very low for lean mass and fat mass changes.
• These changes reflect masculinizing effects expected from testosterone-based hormone therapy.

No significant changes in waist circumference were observed in either AMAB or AFAB individuals undergoing GAHT.

• Waist circumference was analyzed as one of the primary outcomes alongside BMI, body fat, and lean mass.
• GRADE certainty of evidence was low to very low for waist circumference changes.
• The lack of significant WC change contributed to the authors' conclusion that GAHT changes do not appear directly linked to cardiovascular risks.

The systematic review and meta-analysis followed PRISMA guidelines and included cohort, case-control, and clinical trial studies from four databases.

• The search was conducted from April–September 2022 and updated in March 2025.
• A total of 1,896 studies were initially identified; 29 were included in the systematic review and 28 in the meta-analysis.
• Outcomes analyzed included BMI, body fat, lean mass, and waist circumference.
• Evidence certainty was assessed using the GRADE framework, yielding moderate certainty for BMI and low to very low certainty for other outcomes.

The body composition alterations associated with GAHT align with expected outcomes for transgender individuals and do not appear directly linked to cardiovascular risks.

• AMAB individuals' increased fat mass and decreased lean mass mirror typical female body composition patterns.
• AFAB individuals' increased lean mass and decreased fat mass mirror typical male body composition patterns.
• The absence of significant waist circumference changes supports the conclusion regarding limited direct cardiovascular risk.
• The authors note that GAHT is 'generally considered safe' while acknowledging ongoing debate about effects on adipose tissue.