Introduction: Cross-sex hormone therapy is part of the treatment of individuals with gender dysphoria and affects several factors such as body composition and thereby cardiovascular risk. However, little is known about the specific effects on body weight and fat percentage in the first year of treatment.
Aim: The aim of this study is to examine the effects of cross-sex hormones on body weight and total fat percentage during the first year of treatment.
Methods: This prospective study (part of the ENIGI project) included 140 patients that completed one year of treatment. 70 male-to-female individuals (MtFs) received cyproteronacetate (50 mg/day). Of them, 31 MtFs were treated with an estradiol patch (200 μg/week) and 39 MtFs received estradiol valerate (24 mg/day). 70 female-to-male individuals (FtMs) were treated, of which 39 FtMs got testosterone esters intramuscular (250 mg/2 weeks) and 4 FtMs received testosterone undecanoate intramuscular (1000 mg/12 weeks). 27 FtMs were treated with testosterone gel (50 mg/day). At the start and after 12 months of treatment their body weight was measured and a DEXA was obtained.
Results: At baseline the mean body weight of the MtFs was 77.5 kg (S.D.±16.8), which in one year increased to 79.7 kg (S.D.±17.0) with a mean difference of 2.2 kg (95% CI 0.73.8). Their mean total fat percentage increased with 4.0% (95% CI 3.05.0), from 25.0 to 29.0%. The mean body weight of the FtMs increased from 69.1 kg (S.D.±15.0) to 72.2 kg (S.D.±14.7) with a mean difference of 3.1 kg (95%CI 2.0-4.3). In FtMs, a 4.3% (95%CI −5.3 to −3.3) decrease in total fat percentage was seen, from 34.7 to 30.4%.
Conclusions: Despite an expected increase in fat percentage in MtFs and a decrease in FtMs, total body weight increased in both groups. Further research is needed to elucidate the mechanism of weight gain during cross-sex hormone treatment.