Experts have called for large-scale trials after a study suggested that a muscle growth drug could significantly reduce the loss of lean body mass in people using slimming injections. While GLP-1-based jabs like Wegovy and Mounjaro are effective for weight loss, concerns have been raised that up to 40% of weight lost comes from lean mass, including muscle, rather than fat alone.
Study Details
Researchers in the US divided 102 participants into two groups: one received the monoclonal antibody apitegromab alongside tirzepatide (the active ingredient in Mounjaro), while the other received a placebo with tirzepatide. After 24 weeks, total weight loss was similar, but the apitegromab group lost an average of 1.6 kg of lean mass (14.6% of total loss), compared to 3.5 kg in the placebo group—a 55% greater retention of lean mass.
Expert Opinions
Professor Alexander Miras, an obesity expert at Ulster University, called the findings important. He noted that GLP-1 drugs improve functionality but can reduce muscle strength. This new medication may help preserve muscle, enhancing everyday activities like lifting weights or walking uphill.
Professor Naveed Sattar from the University of Glasgow emphasized the need for larger, longer trials to confirm safety and benefits. In the meantime, he advised that people on weight-loss drugs should be supported to increase physical activity in an enjoyable and sustainable way to maintain muscle mass.
The study, published in Nature Medicine and funded by Scholar Rock, had limitations including a small sample size, short duration, and predominantly female participants. Side effects were similar between groups and mostly mild.
