Effects of Gender-Affirming Hormone Therapy on Body Fat: A Retrospective Case- Control Study in Chinese Transwomen

Background: There is limited data on the effects of gender-affirming hormone therapy on body fat changes in Chinese transwomen. It's unclear whether hormone therapy affects obesity and blood lipid levels in this population.The purpose of this study was to evaluate the effects of gender-affirming hormone therapy and treatment duration on the re-accumulation and distribution of body fat in Chinese transwomen. Methods The study included 40 transwomen who had not received gender-affirming hormone therapy and 59 who had. Body fat distribution and blood lipid levels were measured. The study also stratified participants based on the duration of gender-affirming hormone therapy to assess its impact on body fat distribution. Results After receiving gender-affirming hormone therapy, total body fat increased by 19.65% ( P =  0.02) and the percentage of body fat increased by 17.63% ( P =  0.004). The arm and leg regions showed the most significant increases in fat content (+ 24.02%, P =  0.005 and + 41.47%, P< 0.001, respectively) and percentage (+ 25.19%, P< 0.001 and + 30.39%, P< 0.001, respectively). Total visceral fat content decreased (-37.49%, P =  0.008). There was no significant change in the risk of obesity according to the diagnostic criteria for body mass index ≥ 28 or body fat percentage ≥ 25% or 35%. TC levels (-10.45%, P = 0.011) decreased significantly. Fat distribution and changes in those who received gender-affirming hormone therapy for 1–2 years were significantly different from those who did not receive gender-affirming hormone therapy. Conclusion After receiving gender-affirming hormone therapy, the total body fat, and regional fat increased in Chinese transwomen, and body fat distribution changed from masculine to feminine, especially during the first two years. However, visceral fat content declined, and the increase in total body fat percentage did not lead to significant changes in the incidence of obesity, nor did triglyceride and low-density lipoprotein-cholesterol.