Effects of sex steroid hormones on regional fat depots as assessed by magnetic resonance imaging in transsexuals

We investigated prospectively the effect of sex steroids on regional fat de pots and thigh muscle mass in adult transsexuals. Ethinyl estradiol in comb ination with cyproterone acetate, a progestational antiandrogen, was given to 20 male-to-female (M-F) transsexuals, and parenteral testosterone esters were given to 17 female-to-male (F-M) transsexuals. Before and after 12 mo of cross-sex hormone administration, several anthropometric measurements ( weight, skinfolds, body circumferences, and bioimpedance) were performed, a nd transverse magnetic resonance images were obtained at the level of the a bdomen, hip, and thigh to quantify fat depots (subcutaneous and visceral) a nd muscle areas. We observed that treatment with ethinyl estradiol in M-F t ranssexuals induced a significant increase in all subcutaneous fat depots, with a lesser but proportional and significant increase in the visceral fat depot and a decrease in thigh muscle area. Testosterone administration in F-M transsexuals markedly increased thigh muscle area, reduced subcutaneous fat deposition at all levels measured, but slightly increased the visceral fat area. We conclude that sex steroid hormones are important determinants of the sex-specific localization of body fat.