SUN-534 Effect of Cross-Sex Hormone Therapy on Body Composition, Visceral Adipose Tissue, and Bone Mineral Density in Transgender Men

In transgender men (FtM), testosterone therapy may induce changes in different body compartments. The aim of this study was to evaluate body fat and muscle mass, visceral adipose tissue and bone mineral density in FtM transgender individuals receiving cross-sex hormone therapy (CSHT). Sixty two FtM were included in the protocol and performed laboratory tests and dual energy X-ray absorptiometry (DXA) after 3 months of standard CSHT. The median age was 27.0 (21.5-35) years, BMI 25.8 (23.3-32.2) kg/m², and 53% of them had previously used testosterone therapy. Transgender men were compared with 23 natal men controls. Testosterone median levels were 2.03 ng/dl (0.29—5.12) and 4.75 ng/dl (3.47-5.48) in FtM and control individuals, respectively. Estradiol and SHBG were 52.8 pg/ml (30.0-96.2) and 25.2 nmol/l (19.4-49.1) in FtM, and 19.8 pg/ml (14.8-29.1) and 27.9 nmol/l (22.0-37.6) in controls. Transgender men were similar to male controls regarding age (p=0.149), weight (p=0.672), BMI (p=0.189), total fat mass (p=0.461), android / gynoid fat ratio (p=0.674), visceral adipose tissue (p=0.311), total lean mass (p=0.065) and L1L4, femoral neck and total hip BMD. Lean mass index (FNIH) was significantly lower in the FtM individuals [0.724 (0.623-0.825) vs. 0.923 (0.609-1.112), p=0.002]. A positive correlation was observed between testosterone levels and total lean mass (r=0.266, p=0.040) and FNIH index (r=0.378, p=0.003), while a negative correlation was found between SHBG levels and total lean mass (r= -0.348, p=0.008), android / gynoid fat ratio (r= -0.426, p=0.001) and visceral adipose tissue (r= -0.363, p=0.008). A subgroup of 23 FtM performed a second densitometry after a mean of 25.3±8.8 months, with the same equipment. No changes were observed regarding testosterone, SHBG and estradiol levels during this period. Significant Increase in the android / gynoid fat ratio [0.44 (0.32-0.52) vs. 0.48 (0.34-0.54); p=0.017] and decrease of the gynoid fat [43.4±8.3% vs 41.3±8.8%, p=0.05) were observed after CSHT. BMD remained stable along the time. Visceral adipose tissue varied from 522cm³ (117-988) to 612cm³ (271-1.172, p=0.054) after CSHT. In conclusion, preliminary results from this pilot study suggest that lean and fat mass parameters in FtM under CSHT are similar to natal men controls and that testosterone therapy is effective, but might increase abdominal and visceral fat in transgender men. Further studies with larger sample size are needed in order to confirm these findings.