Changes in regional body fat, lean body mass and body shape in trans persons using cross-sex hormonal therapy: results from a multicenter prospective study

Objective: Cross-sex hormonal therapy (CHT) in trans persons affects their total body fat and total lean body mass. However, it is unknown how separate body regions are affected and whether these changes alter body shape. Therefore, the aim of this study was to determine the effects on body fat and lean body mass in separate body regions and on body shape after one year of CHT. Design and methods: In a multicenter prospective study at university hospitals, 179 male-to-female gender dysphoric persons, referred to as transwomen, and 162 female-to-male gender dysphoric persons, referred to as transmen, were included. All underwent whole-body dual-energy X-ray absorptiometry and anthropometric measurements before and after one year of CHT. Results: In transwomen, increases in body fat ranged from +18% (95% CI: 13%; 23%) in the android region to +42% (95% CI: 37%; 46%) in the leg region and +34% (95% CI: 29%; 38%) in the gynoid region. In transmen, changes in body fat ranged from -16% (95% CI: -19;-14%) in the leg region and -14% in the gynoid region (95% CI: -16%;-12) to no change in the android region (+1%, 95% CI: -3%; 5%). Waist-to-hip ratio (WHR) decreased in transwomen (-0.03, 95% CI: -0.04;-0.02) mainly due to an increase in hip circumference (+3.2 cm, 95% CI: 2.3; 4.0). Transmen have a decrease in hip circumference (-1.9 cm, 95% CI: -3.1;-0.7) resulting in an increase in WHR (+0.01, 95% CI: 0.00;0.02). Conclusions: CHT causes a more feminine body fat distribution and a lower WHR in transwomen and a more masculine body fat distribution with a lower hip circumference in transmen.