Muscle Growth Drug Could Preserve Lean Tissue During Weight Loss Treatments

The Lead

A new study reveals that apitegromab, a drug promoting muscle growth, could significantly reduce the loss of lean body mass when using popular weight-loss medications like tirzepatide (found in Mounjaro). This breakthrough addresses a significant concern with current weight-loss treatments that cause patients to lose muscle along with fat.

The Scientific Breakthrough

GLP-1 based weight-loss jabs such as Wegovy and Mounjaro have proven highly effective for people who are overweight or obese, but studies show 25-40% of total weight loss comes from reduction in lean body mass – non-fat components including muscle. This matters because lean body mass is important for physical strength, burns more calories than fat tissue, and is linked to a lower risk of type 2 diabetes.

Apitegromab works by blocking myostatin, a protein involved in inhibiting muscle growth. In a small trial, researchers in the US randomly divided 102 participants into two groups: 51 received apitegromab alongside tirzepatide, while the other 51 received a placebo with tirzepatide.

The Clinical Trial Results

After 24 weeks, the trial revealed that total weight loss was similar between the two groups. However, participants given apitegromab alongside tirzepatide lost on average 1.6kg (3.5lb) of lean mass (14.6% of total weight loss), while those given tirzepatide with a placebo lost an average of 3.5kg of lean mass. This means apitegromab was associated with a 55% greater retention of lean mass relative to placebo.

The study had limitations, including that most participants were women and the trial was small and short in duration. However, the number of people experiencing side-effects was similar between the two groups, with most deemed to be mild.

The Implications for Weight Loss Treatment

Prof Alexander Miras, an obesity expert at Ulster University not involved in the work, described the findings as very important. While GLP-1s have been associated with improved "functionality" – making everyday activities easier – they've also been linked to loss in muscle mass and strength. This new medication may help reduce these effects and improve functionality even further.

Prof Naveed Sattar, a cardiometabolic medicine expert at the University of Glasgow, emphasized that larger-scale and longer trials are needed to confirm safety and actual health benefits. In the meantime, he recommended that people prescribed weight-loss drugs should be supported to increase physical activity, which can help maintain muscle mass in a physiological way.

The Future of Weight Loss Therapies

The findings suggest a promising direction for weight-loss treatments that preserve muscle mass while reducing fat. As the popularity of GLP-1 based medications continues to grow, addressing muscle loss could become an important focus for pharmaceutical companies and healthcare providers.

Future research will need to confirm the long-term safety and effectiveness of combining apitegromab with weight-loss medications. If successful, such combinations could become standard practice, potentially improving patient outcomes and quality of life during weight loss journeys.