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.

DESIGN: Retrospective cohort study.

SETTING: Gender identity clinic.

PARTICIPANTS: 380 trans boys and 168 trans girls treated with PS prior to GAHT.

MAIN OUTCOME MEASURES: Total lean- and fat mass Z-scores using birth-assigned sex as reference 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. Only during the first year of testosterone, 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). In trans girls, both lean and fat mass Z-scores gradually changed over three years of PS (respectively -1.13, 95%CI -1.29; -0.98 and 1.06, 95%CI 0.90; 1.23). Only 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 three years (-0.02, 95%CI -0.20; 0.16).

CONCLUSIONS: Compared to 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 one 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.