You start testosterone replacement therapy (TRT) expecting more energy, a higher libido, and easier weight loss. A month in you’re starting to feel the first two, but instead of leaning out, you’ve gained weight. Is the uptick on the scale a side effect of testosterone, or is something else at play?
Taking testosterone can help increase lean muscle mass and decrease fat mass, but it isn’t a one-way ticket to weight loss. “If you were to just take testosterone and do nothing, you’d probably gain weight,” says urologist Thomas Masterson, M.D.
Here’s how testosterone affects your metabolism—and what you can do to stay on track.
About the Experts
Justin Dubin, M.D., is a urologist and men’s health specialist in South Florida.
Thomas Masterson, M.D., is an assistant professor of urology at the Desai Sethi Urology Institute in the Miller School of Medicine at the University of Miami.
Amy Pearlman M.D., is a board-certified urologist and men’s health specialist in Coral Gables, Florida.
Starting TRT can sometimes make it seem like you’re gaining weight rather than losing it. But before you panic, know this: Your body is adjusting to increased testosterone levels, which can initially affect your baseline testosterone and estrogen levels—and your body composition— in unexpected ways (1).
“When my patients gain weight on TRT, it’s usually due to water retention, increased muscle mass, and sometimes increased hunger, leading to increased food intake,” says urologist Amy Pearlman, M.D.
The numbers on the scale don’t tell the entire story. Pearlman says your “weight gain” might not be fat gain at all. You could have gained lean muscle or have water weight gain.
Muscle mass
Muscle is denser than fat, so it weighs more by volume. TRT stimulates muscle growth, so while your clothes may be looser, the scale might not budge—or could even go up (2). That doesn’t mean you’re not losing fat (2). Testosterone ignites protein synthesis, strengthening muscle fibers and increasing lean mass (3)
A systematic review found that obese men treated with TRT gained an average of 4.4 pounds of muscle in a 6-month time period while also experiencing a drop in low-density lipoprotein (LDL), or “bad” cholesterol (4). Testosterone ignites protein synthesis, strengthening muscle fibers and increasing lean mass (3).
A systematic review found that obese men treated with TRT gained an average of 4.4 pounds of muscle in a 6-month time period while also experiencing a drop in low-density lipoprotein (LDL), or “bad” cholesterol (4).
Pairing TRT with strength training and a high-protein, low-carb diet can accelerate muscle growth and body recomposition (5). As Masterson points out, “testosterone by itself isn’t a silver bullet. You still have to exercise and consider your diet to meet weight loss and muscle gain goals.”
Fast, Easy, Affordable
Hone’s at-home testosterone assessment is the simplest way to uncover whether your levels are low. If you qualify for treatment, TRT can be sent right to your door.
A 2015 study in the Journal of Obesity revealed that water retention tends to increase within the first 3 to 6 months of starting TRT (6). One reason? The body converts some testosterone into estradiol, a form of estrogen, through an enzyme called aromatase (7).
While estrogen is thought of as a women’s hormone, men need it to help regulate sex drive, sperm production, and erectile function (8). However, it can cause water retention (9).
Another culprit: increased appetite. TRT can ramp up hunger, leading to higher food intake and, in turn, more fluid retention.
Body composition
Fat tissue contains aromatase, the same enzyme that converts testosterone to estradiol (10). The more body fat you have, the greater the likelihood of this conversion—sometimes leading to estrogen-related side effects like gynecomastia (aka “man boobs”). In fact, 10-25% of men on TRT experience breast tenderness or enlargement due to excess estrogen (10, 11).
“If the TRT results in an elevated estradiol and my patient has symptoms of hyperestrogenism, including breast/nipple tenderness, I will reduce the TRT dose,” Pearlman says.
Working out and having healthier eating habits are necessary to change body composition, says urologist Justin Dubin, M.D.
The Benefits of Testosterone Replacement
Studies show testosterone replacement therapy can help improve insulin resistance and cholesterol levels, and reduce body fat all of which can help with weight loss (11). And research shows that losing weight can reduce the risk of heart disease, stroke, and type 2 diabetes (12). TRT can also improve erectile dysfunction, increase sex drive, improve mental health, and boost bone density (9).
Symptoms of Low Testosterone
Men who have low testosterone experience low sex drive, erectile dysfunction, fatigue, and hair loss. Dubin notes that men with low testosterone likely won’t have as much energy either. “This can make it more difficult to get motivated to exercise regularly and lose weight,” he says. “It’s a cyclical problem.”
Bottom Line
TRT supports weight loss, but it can also push the number on the scale higher. This “weight gain” is likely due to increased muscle mass or water retention. To ensure that any weight gain is muscle—not fat—pair TRT with a solid nutrition and exercise plan. Strength training, a high-protein diet, and regular movement can help maximize TRT’s benefits while minimizing unwanted weight gain.
David Hopper is a freelance writer and editor with over 15 years of experience. He has worked as a reporter and copy editor at several newspapers and online media outlets. In recent years, he has focused on health journalism, primarily writing about men’s health and sexual health topics.
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