Rates of Obesity, Weight Gain Up for Transmasculine Individuals

Transmasculine individuals have greater rates of obesity and increased weight gain before and during hormone therapy compared with transfeminine individuals, according to a study published online Aug. 16 in the International Journal of Obesity.

Mabel Kyinn, M.D., from The George Washington School of Medicine & Health Sciences in Washington, D.C., and colleagues conducted a longitudinal study involving 470 transgender and gender-diverse adults (247 transfeminine and 223 transmasculine). Body weight and body mass index were measured at baseline and at multiple follow-up visits during 57 months after initiation of gender-affirming hormone therapy.

The researchers found that in the transmasculine group, the mean body weight increased by 2.35 kg within two to four months of starting gender-affirming hormone therapy and further increased beyond 34 months. In the transfeminine group, for the first 21 months of hormone therapy, mean body weight was stable and then began to increase steadily, especially in those aged younger than 30 years. At baseline, the prevalence of obesity was 25 and 39 percent in the transfeminine and transmasculine groups, respectively. The rates of obesity ranged from 21 to 30 percent and from 42 to 52 percent in the transfeminine and transmasculine groups, respectively, following initiation of hormone therapy. After 11 to 21 months of hormone therapy, weight gain of ≥5 kg occurred in 21 and 30 percent of transfeminine and transmasculine individuals, respectively.

"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," a coauthor said in a statement. "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."