Weight Gain Common With Testosterone in Trans Men

Miriam E. Tucker

September 03, 2021

Obesity and weight gain are common during gender-affirming hormone therapy (GAHT) in transgender individuals, particularly among trans males, new research finds.  

The doctors followed 247 trans female and 223 trans male individuals from baseline through nearly 5 years of gender-affirming hormone therapy. The prevalence of obesity was high in the trans male group at baseline.

Rapid weight gain occurred within the first few months of GAHT initiation in trans males, while weight gain occurred later in trans females.

"The rapid weight gain that trans men saw within the first 2 to 4 months of starting the testosterone suggests that it is related to the testosterone. Testosterone is known to increase muscle mass and cause fluid retention," explained the study's senior author, Michael S. Irwig, MD, of Beth Israel Deaconess Medical Center, in an interview with Medscape Medical News.

On the other hand, Irwig said, "the lack of weight changes in most trans women tells me that the spironolactone and estrogen didn't really have much of an effect on their weight since it didn't change in the first 1 to 2 years. When they gained weight after that it could be just due to aging and other factors not related to the hormones."

In any case, Irwig noted, the clinical solution is to apply the same lifestyle modification and risk factor reduction to transgender individuals as to any other patient with excess weight.

"Hormones are generally such an important part of a transgender person's life that not taking the hormones is not an option, even if it may cause weight gain," he said.

"Even with a possible increased heart disease risk, people are going to say it's a risk they're willing to take because the hormones give them what they need. So, the key is really to make sure all those risk factors are controlled...If their weight is excessive, make sure they're exercising, refer them to a weight management program. It really is general primary care stuff not to be neglected," Irwig continued.

However, he added that there may be more urgency in the trans male population that starts on GAHT because the weight gain can be fairly dramatic. In this study, weight gain was more than 5.4 kg (12 lb) within 11 to 21 months of starting therapy in 21% of participants overall and in about a third of trans men.

"That's a significant amount of weight...and we don't know what happens after that."

Baseline Obesity Rates High, Further Increases in Trans Males

In this observational study, the largest and longest of its kind to date, 470 transgender individuals were treated at an academic medical center and nonprofit community health center in Washington, DC, from 2007 through mid-2015. Several measures of body weight were used.

Participants were a mean age of 27.8 years, 27% were non-White, and 16% were Latinx. At baseline, 39% of trans males and 19% of trans females had a body mass index (BMI) ≥ 30 kg/m2, report Mabel Kyinn, MD, The George Washington School of Medicine & Health Sciences, Washington, DC, and colleagues in the study, published in the International Journal of Obesity.

Trans males took testosterone (mostly intramuscular), while trans females took a combination of estrogen (mostly oral estradiol) and an antiandrogen (> 90% spironolactone over the first 2 years of the study, declining thereafter). Follow-up continued through 57 months.

Among the trans male patients, within the first 2-4 months of starting GAHT, mean body weight increased by 3%-4%, with a mean weight gain of about 2.4 kg (5.3 lb).

Obesity prevalence (BMI ≥ 30 kg/m2) rose from 39% to 44%. Mean body weight stabilized after that, but rose again by another 3.3 kg (7.3 lb) after 34 months of testosterone therapy.

At that point, 52% had a BMI ≥ 30 kg/m2.

Weight gain was greater among those aged 17-29 years at GAHT initiation compared with those aged ≥ 30 years.

Among trans females, body weight and BMI remained relatively stable for the first 21 months of GAHT. After that, there was a significant weight gain of about 2.0-4.9 kg among those aged 17-29 years, but not those aged ≥ 30 years. Mean BMI and obesity rates were higher in the Latinx group than the others.

Don't Be Afraid to Talk to Transgender Patients About Weight

"Body weight and BMI should be routinely monitored before and after the initiation of GAHT. Multidisciplinary weight reduction interventions should be promoted where appropriate," write Kyinn and colleagues.

Irwig said the weight gain in trans male 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." 

Clinicians shouldn't be afraid to raise the issue with patients, he stressed.

"Often weight management services are neglected. There's a lot of stigma and fear of offending patients. A lot of doctors don't want to bring it up," Irwig said.

"But it's such a huge problem and is linked to so many adverse health conditions, including 10% of cancers. If we can get obesity rates down, we can prevent cancers, heart attacks, sleep apnea, hypertension, diabetes...all of these things that are linked to obesity," he noted.  

Irwig has reported no relevant financial relationships.

Int J Obes (Lond). Published online August 16, 2021. Abstract

Miriam E. Tucker is a freelance journalist based in the Washington, DC, area. She is a regular contributor to Medscape, with other work appearing in the Washington Post, NPR's Shots blog, and Diabetes Forecast magazine. She is on Twitter @MiriamETucker.

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