Gender-affirming hormone therapy (GAHT) is a fundamental component of medical transition in transgender men, promoting body composition changes that align physical characteristics with gender identity and alleviate gender dysphoria. In adults, GAHT typically involves testosterone administration, whereas adolescents may receive gonadotropin-releasing hormone agonists to suppress puberty before initiating testosterone. Despite its general safety when appropriately monitored, findings on GAHT-related changes in body composition and potential cardiovascular implications are inconsistent. Accurate assessment of skeletal muscle mass and fat redistribution is clinically relevant, as conventional anthropometric measures may fail to capture these changes. This study evaluates body composition changes after one year of testosterone therapy in transgender men using bioelectrical impedance vector analysis (BIVA), and explores the utility of muscle ultrasound as an accessible tool for monitoring skeletal muscle and potential differences among testosterone formulations.
Gender-affirming hormone therapy (GAHT) is a central component of medical transition in transgender men, and aims to induce body composition changes that align physical appearance with gender identity and reduce gender dysphoria. In adults, GAHT typically consists of testosterone administration, whereas, in adolescents, gonadotropin-releasing hormone agonists (GnRHa) may be used to suppress puberty before initiating testosterone. GAHT has been associated with improvements in psychological well-being, social integration, and quality of life, although evidence remains limited due to the lack of randomized clinical trials. Moreover, body composition changes have been linked to psychological health in this population. GAHT is considered safe when adequately monitored and individualized according to cardiovascular risk profile and pre-existing conditions. However, current evidence regarding its effects on body composition and potential implications for cardiovascular risk is inconsistent. Clinically, it is particularly relevant to determine the extent to which GAHT supports gains in skeletal muscle mass and fat redistribution, given their influence on body satisfaction and cardiometabolic risk. Importantly, relying on basic anthropometric measures such as body weight may lead to an underestimation of cardiovascular risk by failing to capture changes in key body compartments. Reference techniques such as DXA or magnetic resonance imaging have been used to characterize these changes, although their limited accessibility restricts their routine application in clinical follow-up. In this context, bioelectrical impedance vector analysis (BIVA) and muscle ultrasound emerge as accessible alternatives for assessing skeletal muscle mass. However, the lack of population-specific reference values may hinder interpretation, underscoring the need to develop dedicated standards and validate these methods in transgender populations. To examine the effect of one year of testosterone treatment on body composition in transgender men, different parameters will be assessed using BIVA. Additionally, the utility of muscle ultrasound as a feasible tool for monitoring skeletal muscle during masculinization will be explored, as well as if there are differences in body composition between different types of testosterone formulations.
Study Type
OBSERVATIONAL
Enrollment
70
Participants will be treated with testosterone according to the World Professional Association for Transgender Health (WPATH) guidelines. Pharmaceutical presentation of testosterone will be consensually chosen by participants together with their endocrinologists. This include 1,000 mg of intramuscularly administered testosterone undecanoate every 6 weeks after initiation of GAHT and then every 12 weeks (and, in case of testosterone undecanoate stock-out, with 200-250 mg of intramuscularly administered testosterone cypionate), or 50 mg/day of transdermic testosterone gel (Tgel), according to European guidelines. For adolescents, GAHT may be combined with puberty suppression using gonadotropin-releasing hormone agonist (GnRHa), when indicated, and these agents will be continued in adults if menses persisted despite testosterone escalation.
FISABIO
Valencia, Valencia, Spain
Examine the increase in skeletal muscle mass after one year of testosterone treatment on body composition in transgender men using bioelectrical impedance vector analysis.
To assess if there is a significant skeletal muscle mass gain after one year of testosterone treatment, skeletal muscle mass will be predicted using predictive equations with both resistance and resistence measured using bioelectrical impedance vector analysis. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (\<0.05) with a 95% confidence interval.
Time frame: 5 years
Explore the utility of muscle ultrasound as a feasible tool for monitoring skeletal muscle during masculinization hormonal treatment
Muscle ultrasound will be performed on a subsample using a DP-50 Expert Mobile Ultrasound System (Mindray®) equipped with a 5-10 MHz linear transducer. Examinations will be conducted at baseline, 6 months, and 12 months. Participants will be positioned supine with legs extended and instructed to refrain from exercise for at least 30 minutes before testing. Images will be obtained at the midpoint between the anterior superior iliac spine and the patella. Bilateral quadriceps muscle thickness (right and left; RQU and LQU) will be measured as the distance between the superficial and deep aponeuroses. Thickness of the rectus femoris and vastus intermedius will be recorded along the transverse axis. To check if RQU and LQU can predict skeletal muscle mass gain, regression models will be performed (square R coefficient \> 0,6). Acceptable sensitivity and specificity from RQU and LQU as predictors of skeletal muscle mass will be considered if their values are above 70%.
Time frame: 5 years
Assess significant changes in skeletal muscle mass gain according to type of testosterone formulation used
Skeletal muscle mass gain will be assessed by calculating the difference between final and baseline values obtained from body composition evaluations. Significant differences between types of testosterone formulations will be considered when notable differences in mean values between groups are observed, as determined by a p-value \< 0.05 using multiple pairwise comparisons followed by post hoc analysis, with a 95% confidence interval.
Time frame: 5 years
Evaluate significant changes in visceral fat after one year of testosterone treatment
Visceral fat will be measured by bioelectrical impedance. It is considered to be high when \> 1,1 L. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (\<0.05) with a 95% confidence interval.
Time frame: 4 years
Quantify skeletal muscle mass gain through one year of testosterone treatment
Quantification of skeletal muscle mass gain will be performed by calculating the difference between baseline (prior to treatment) and final (after one year of treatment) values obtained from bioelectrical impedance analysis. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (\<0.05) with a 95% confidence interval.
Time frame: 4 years
Assess significant changes in high-sensitivity C-reactive protein (hs-CRP) as an inflammatory parameter after one year of testosterone treatment.
Participants will be considered to have achieved an improvement in high-sensitivity C-reactive protein levels if they normalize its value (normality values defined between 0 and 1.69mg/dl).
Time frame: 4 years
Evaluate if there is a significant reduction after one year of testosterone treatment in HOMA-IR levels.
The Homeostatic Model Assessment (HOMA-IR) index is calculated by multiplying fasting plasma insulin by fasting glucose and dividing the result by a constant (405 when glucose is expressed in mg/dL). Participants will be considered to have achieved an improvement in high-sensitivity C-reactive protein levels if they normalize its value (normality values defined between 0 and 3,8).
Time frame: 4 years
Analyze the changes in ApoB/ApoA1 ratio after one year of gender-affirming hormone therapy.
ApoB and ApoA1 ratio will be calculated using both parameters, in order to assess if there are significant changes in lipid profile in transgender men using testosterone treatment. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (\<0.05) with a 95% confidence interval.
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Time frame: 4 years
Evaluate significant changes in anti-mullerian hormone levels after one year of testosterone treatment.
A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (\<0.05) with a 95% confidence interval.
Time frame: 4 years
Evaluate the changes in inhibin B levels after one year of gender-affirming hormone therapy.
A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (\<0.05) with a 95% confidence interval.
Time frame: 4 years
Evaluate significant changes in hand grip strength after one year of testosterone treatment.
Hand grip strength will be measured using a Jamar® Plus+ digital dynamometer in the non-dominant hand. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (\<0.05) with a 95% confidence interval.
Time frame: 5 years