1 Department of Endocrinology and Center of Expertise on Gender Dysphoria, VU University Medical Center, Amsterdam, The Netherlands; 2 Department of Endocrinology, Ghent University Hospital, Ghent, Belgium; 3 Department of Endocrinology, Oslo University Hospital, Oslo, Norway; 4 Sexual Medicine and Andrology Unit, Department of Experimental, Clinical and Biomedical Sciences, University of Florence, Florence, Italy.

Introduction: Fat distribution is an important secondary sex characteristic, which is generally peripherally or pear-shaped (gynoid) in females and centrally or apple-shaped (android) in males. Total body fat increases in male-to-females (MtFs) and decreases in female-to-males (FtMs) during cross-sex hormone therapy (CSHT), approaching body fat amounts of the desired sex. However, changes in android or gynoid fat distribution might be a better measure for masculinization and feminization than changes in amount of body fat per se. As yet, the exact effects of CSHT on fat in the android- and gynoid region are unknown.

Aim: To investigate the effects of CSHT on android fat, gynoid fat and waist-hip ratio (WHR) in MtFs and FtMs.

Methods: This prospective study (ENIGI) included 108 patients that completed one year of CSHT. 51 MtFs received anti-androgens and estrogen therapy, while 57 FtMs were treated with androgens. At the start and after one year of CSHT anthropometrics were measured and a whole body DEXA was obtained, in which android fat and gynoid fat were measured.

Results: In MtFs an increase of gynoid fat was seen of +0.8 kg (0.6;1.1) from 3.3 to 4.1 kg. Android fat tended to increase with 0.1 kg (−0.02;0.3) from 1.6 to 1.7 kg, but WHR decreased with −0.02 (−0.001;−0.01) from 0.86 to 0.84. In FtMs, gynoid fat decreased with −0.6 kg (−0.4;−0.8) from 4.8 to 4.2 kg. Android fat and the WHR tended to increase with respectively 0.05 kg (−0.06;0.2) from 1.89 to 1.94 kg and 0.02 (−0.01;0.04) from 0.81 to 0.83.

Conclusion: Fat distribution in MtFs changed towards a more female-like fat distribution with an increase in gynoid fat and a trend towards a decreasing WHR. The opposite tended to occur in FtMs with a decrease in gynoid fat and an increase in android fat and WHR.