Apitegromab trial shows 55% greater lean mass retention
Apitegromab helped people losing weight with tirzepatide retain more lean body mass in a 24-week phase 2 trial, according to researchers in the US. The study found 55% greater retention of lean mass, while total weight loss stayed similar in both groups.
Nature Medicine trial
Researchers randomly divided 102 participants into two groups, with 51 given apitegromab alongside tirzepatide and 51 given placebo with tirzepatide. The participants receiving apitegromab lost 1.6kg of lean mass on average, compared with 3.5kg in the placebo group.
That 1.6kg represented 14.6% of total weight loss. Most of the participants were women, and the trial was funded by Scholar Rock, the producer of apitegromab.
Muscle strength concerns
Apitegromab is a monoclonal antibody that blocks myostatin, a protein involved in inhibiting muscle growth. Studies suggest that 25-40% of total weight loss from GLP-1 based drugs can come from a reduction in lean body mass, which includes muscle.
Alexander Miras, an obesity expert at Ulster University, called the findings very important and said the medication may help reduce the effects of GLP-1-based drugs on muscle strength. He said, “This means that [people] may be less able to lift heavy weights, for example, or walk up a hill” and added, “This new medication may help reduce the effects of GLP-1-based drugs on muscle strength and therefore improve functionality even further compared to someone not on the new medication who is just taking tirzepatide.”
Naveed Sattar on activity
Naveed Sattar, a cardiometabolic medicine expert at the University of Glasgow, said, “This is an early-stage trial that suggests novel drugs can help mitigate muscle mass loss with prescribed tirzepatide. However, it’s too early to say whether this actually benefits peoples health or ability to move or function better”
He also said, “In the meantime, people prescribed these drugs should be supported to increase their physical activity, as this can help maintain muscle mass in a physiological way. Importantly, activity should also be framed as something enjoyable and sustainable, rather than purely as a medical add‑on,”
The side-effects were similar in both groups, and most were mild. Because the study was small and short in duration, the result points to a possible way to limit lean mass loss during weight loss treatment, but not yet to a proven long-term change in health or function.
