Time Course of Body Composition Changes in Transgender Adolescents During Puberty Suppression and Sex Hormone Treatment

Context Transgender adolescents can undergo puberty suppression (PS) and subsequent gender-affirming hormone therapy (GAHT) but little information is available on the expected rate of physical changes.Objective To investigate the time course of body composition changes during PS and GAHT.Methods In this study, retrospective data of 380 trans boys and 168 trans girls treated with PS prior to GAHT from a gender identity clinic were included. Total lean and fat mass Z-scores using birth-assigned sex as reference were determined using dual-energy X-ray absorptiometry.Results In trans boys, lean mass Z-scores decreased (-0.32, 95% CI -0.41; -0.23) and fat mass Z-scores increased (0.31, 95% CI 0.21; 0.41) in the first year of PS and remained stable thereafter. Lean mass Z-scores increased (0.92, 95% CI 0.81; 1.04) and fat mass Z-scores decreased (-0.43, 95% CI -0.57; -0.29) only during the first year of testosterone,. In trans girls, both lean and fat mass Z-scores gradually changed over 3 years of PS (respectively -1.13, 95% CI -1.29; -0.98 and 1.06, 95% CI 0.90; 1.23). In the first year of GAHT, lean mass Z-scores decreased (-0.19, 95% CI -0.36; -0.03) while fat mass Z-scores remained unchanged after 3 years (-0.02, 95% CI -0.20; 0.16).Conclusion Compared with peers, trans girls experienced ongoing lean mass decrease and fat mass increase during 3 years of PS while in trans boys smaller changes were observed that stabilized after 1 year. A large increase in lean mass Z-scores occurred only during the first year of testosterone treatment. In trans girls, body composition changed only slightly during GAHT. This information can improve counseling about treatment effects.