Body composition changes at different stages of therapy for transgender boys vs. girls
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Key takeaways:
- Transgender boys experience a large increase in lean body mass in the first year of testosterone therapy.
- Transgender girls have greater body composition changes during puberty suppression.
Transgender girls see most of their body composition changes occur during puberty suppression, whereas transgender boys experience greater body composition changes during gender-confirming testosterone therapy, according to study data.
In an analysis of data from adolescents undergoing gender-confirming treatment at the Center of Expertise on Gender Dysphoria at the Amsterdam University Medical Center from 1972 to 2018, researchers examined body composition changes over 3 years for youths during puberty suppression and hormone therapy. The researchers found body composition changes occur at different stages of treatment for transgender boys and transgender girls.
“Providers can use the results from the study when counseling adolescents about the effects of hormonal treatment,” Sabine E. Hannema, MD, PhD, a pediatric endocrinologist at Amsterdam University Medical Center, told Healio. “This should help to ensure that adolescents have realistic expectations about the magnitude and time course of changes in body composition.”
Hannema and colleagues obtained data from youths younger than 18 years when puberty suppression began who had at least one whole-body DXA scan performed during puberty suppression or gender-confirming HT treatment. Whole-body fat mass, lean mass and total mass were measured during DXA scans before the start of treatment and at 1-to-2-year intervals during treatment. Z scores were calculated using National Health and Nutrition Examination Surveys reference data. BMI was assessed using height and weight measured at every visit.
Findings from the study were published in The Journal of Clinical Endocrinology & Metabolism.
More changes during HT for transgender boys
Of 380 transgender boys included in the study, 309 had data available during pubertal suppression. Over 3 years of treatment, BMI standard deviation scale remained relatively stable using female references. Lean mass z score declined by 0.32 points at 1 year before remaining stable at years 2 and 3. Total fat mass z score increased by 0.31 points at 1 year and by 0.47 points from baseline to 3 years.
There were 235 transgender boys in the study who underwent testosterone treatment. In this subgroup, BMI standard deviation score using female references increased by 0.27 points at 1 year, but was comparable to the start of HT treatment at 3 years. Lean body mass z score increased by 0.93 points at 1 year and remained stable thereafter. Fat mass z score decreased by 0.43 points at 1 year and by 0.58 points from baseline to 3 years. At 3 years, fat percentage for transgender boys was comparable to a reference group of cisgender men aged 20 years from NHANES.
“The time course of body composition changes with testosterone was somewhat surprising,” Hannema said. “Because in adolescents the dose of testosterone is gradually increased, we had expected a more gradual increase of lean body mass over several years. We found that lean body mass markedly increased in the first year but changed little in the two subsequent years.”
Transgender girls lose lean mass during puberty suppression
There were 168 transgender girls included in the study, of whom 154 underwent pubertal suppression. The group had no changes in BMI standard deviation score using male references at 3 years. Lean mass z score decreased by 1.13 points and fat mass z score increased by 1.06 points from baseline to 3 years. The decrease in lean mass z score was 0.63 points larger at 3 years among transgender girls who had late puberty compared with those who had early puberty.
Body composition data following gender-confirming estrogen therapy was available for 111 transgender girls. BMI standard deviation score for transgender girls was 0.18 points lower than male references at 1 year and remained stable at 2 and 3 years. Lean mass z score decreased by 0.17 points at 1 year and remained stable at years 2 and 3. Fat mass z score at 3 years was comparable to the start of HT. Transgender girls had a lower fat percentage at 3 years than a reference group of cisgender women aged 20 years from NHANES (29.4% vs. 35.1%).
Hannema noted that variation was observed among individual participants in the study and more studies are needed to determine why gender-confirming treatment led to heterogenous responses.
“We found that the pubertal stage at which individuals had started puberty suppression did not affect outcome and we could not show a relation with hormone concentrations either,” Hannema said. “We would like to investigate what determines this variation in response to hormone treatment between people.”
For more information:
Sabine E. Hannema, MD, PhD, can be reached at s.e.hannema@amsterdamumc.nl.
Perspective
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Joshua D. Safer, MD, FACP, FACE
The study represents important data gleaned from the large experience at Amsterdam University Medical Center. There is a developing literature connecting testosterone in transgender people to athleticism connected to muscle and other tissue changes. That said, testosterone levels within the typical male range are not associated with differences in athleticism for cisgender men. The differences observed are associated with testosterone levels rising from the typical female range toward the typical male range.
Typical hormone regimens for transgender people include adding exogenous testosterone for masculinizing treatment and using exogenous estrogens to centrally suppress testosterone for feminizing treatment. The latter leverages the need for some estrogen for feminization in addition to the central testosterone suppression. For youths, there can be a brief period of gonadotropin-releasing hormone (GnRH) agonist treatment to pause puberty while further planning is considered.
The data from the youths in Amsterdam are consistent with expectations. When testosterone levels are increased, there is a notable change in body composition. Beyond a certain testosterone level, however, changes are difficult to see. Opposite changes are noted when testosterone levels decrease below the typical male range. The rise for the transgender masculine individuals occurs when they initiate testosterone therapy. The testosterone rise is not seen if they start with GnRH agonists alone. However, the fall for transgender feminine individuals does not depend on exogenous estrogen necessarily. GnRH agonists suppress the sex hormone axis and decrease testosterone levels on their own.
More detailed analysis of the specific impact of different treatments on different tissues is an important contribution to our understanding of human biology and will be welcome going forward.
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