New drugs for the treatment of obesity: do we need approaches to preserve muscle mass?

The development of drugs targeting Nutrient Stimulated Hormone receptors has ushered in a dramatic change in our approach to weight management because of their ability to achieve weight losses of 10%, 20%, even 30% in significant numbers of patients. Additionally, disease modifying properties of these medications are compelling. Indications now include cardiovascular risk reduction, obstructive sleep apnea and diabetes management, and emerging evidence supports efficacy for heart failure and chronic kidney disease. These medications would need to be taken long term and the population being treated will be older than the traditional weight management patient. Emerging evidence cautions that the loss of excessive lean mass with some of the newer medications may be problematic. This is not a concern for most patients who will need the medications, but it is a concern in an older population, since loss of muscle and bone accelerates and progresses past age 60. Of weight lost with semaglutide, approximately 45% is from lean mass, while with tirzepatide, it is 25%. Going forward, combining another NuSH such as glucagon or amylin with the GLP-1 receptor agonists may lessen loss of lean mass. Another approach under study is the use of MAPi - myostatin-activin pathway inhibitors. Promising results with bimagrumab are spurring investigaton in this area. For the full potential of disease modification to be achieved, it's a given that we must demonstrate safe, long term body composition improvement when the new medications are deployed, especially in the older population. This narrative review discusses the justification for focus on lean mass preservation and reviews the status of relevant drugs in development.