Variation in sensitivity and rate of change in body composition: steps toward individualizing transgender care

Objective: Transgender individuals sometimes report a lack of physical change during hormone treatment, such as alterations in muscle tone or fat distribution. Identifying characteristics of this subgroup could be a step toward individualizing hormone therapy in transgender individuals. Therefore, we study the variation of changes in body composition and characteristics associated with a lack of change. Design and methods: Body composition measures were recorded in 323 transmen and 288 transwomen at every visit from the start of hormone therapy to a maximum of 24 months follow-up. Absence of change was defined as transmen with a decrease in lean body mass or transwomen with a decrease in fat percentage. Results: A lack of change at 24 months was observed in 19 of 94 (20.2%) transmen and in 9 of 96 (9.4%) transwomen. The risk of not achieving change in body composition was related to lower testosterone levels and less suppression of LH in transmen (OR: 0.67, 95% CI: 0.48-0.94 per SD increase in testosterone and OR: 1.36, 95% CI: 1.01-1.83 per SD increase in LH). Conclusions: There is a large variation in body composition changes during hormone therapy, with a substantial proportion of individuals with no measurable effects. In transmen, serum testosterone and LH were associated with a lack of change, but serum hormone levels were not associated with body composition changes in transwomen. The results provide a rationale for individualizing hormone therapy in transmen, by considering individual effects rather than solely relying on a standardized dosage of hormone therapy.