Gender-Affirming Hormone Therapy Associated with Changes in Body Weight

In what investigators call the largest and longest study of its kind, new research details how gender-affirming hormone therapy can influence body weight and rates of obesity among transgender and gender-diverse individuals.

A longitudinal, observational study with at least 2 years of follow-up for each of the 470 patients, results provide evidence demonstrating body weight and body mass index (BMI) should be closely monitored by clinicians before and after initiation of gender-affirming hormone therapy and also suggest transmasculine individuals experienced greater rates of obesity and obesity both before and during hormone therapy than transfeminine individuals.

“Our study is the first to describe the associations between gender-affirming hormone therapy and body weight changes for at least 2 years, and to compare the rates of underweight, normal weight, overweight, obesity and severe obesity using measurements taken before and after hormone treatment,” said Michael S. Irwig, MD, an endocrinologist and director of Transgender Medicine at Beth Israel Deaconess Medical Center (BIDMIC), in a statement. “Because high body weight and obesity are so common in our society, clinicians may forget to address this important issue with their patients and miss opportunities to lower their risk for cardiovascular disease and cancer.”

As investigators point out in their study, the increased prevalence of obesity often leads to this comorbidity being an overlooked aspect of management, particularly among those receiving gender-affirming hormone therapy. With the current study, Irwig and colleagues from BIDMC investigators hoped to expand the current knowledge base surrounding obesity rates and weight changes in adults treated with gender-affirming hormone therapy. Through a chart review of transgender and gender diverse patients who were treated with gender-affirming hormone therapy at the George Washington University or the medical staff at Whitman-Walker Health, investigators identified a cohort of 470 individuals for inclusion in their study.

This patient cohort included 247 transfeminine and 223 transmasculine individuals and this group had a mean age of 27.8 years. For inclusion in the study, individuals needed to be 17 years or older, have a non-cisgender gender identity, and have information related to body weight and BMI at baseline and multiple follow-up visits. Investigators pointed out follow-up clinical visits occurred up to 57 months after initiation of gender-affirming hormone therapy. The primary outcomes of interest were changes to body weight and obesity rates after receiving therapy.

Upon analysis, investigators found the mean body weight in the transmasculine group had increased by 2.35 (IQR, 1.15-3.55) kg within 2-4 months of starting gender-affirming hormone therapy. This continued to increase beyond 34 months. In contrast, mean body weight was stable for the first 21 months of hormone therapy among the transfeminine group. However, investigators pointed out mean body weight began to increase following 21 months, with this increase most apparent among transfeminine individuals less than 30 years old.

At baseline, the prevalence of obesity was 39% in the transmasculine group and 25% in the transfeminine group. When assessing prevalence following initiation of hormone therapy, results indicated the prevalence of obesity ranged from 42-52% among the trans masculine group and 21-30% among the transfeminine group. Additionally, weight gains of 5 kg or more were observed among 30% of transmasculine individuals and 21% of transfeminine individuals following 11-21 months of gender-affirming hormone therapy.

“The weight gain in transmasculine individuals is consistent with previous studies, and testosterone is the most likely reason for the weight gain, as it occurred so soon after initiating therapy,” said Irwig. “Among transfeminine individuals, the onset of weight gain so long after initiating therapy indicates that gender-affirming hormone therapy is playing less of a role in weight gain.”

This study, “Weight gain and obesity rates in transgender and gender diverse adults before and during hormone therapy,” was published in the International Journal of Obesity.