A drug that promotes muscle mass could help retain lean body mass when using weight-loss jabs, a study has suggested.
Weight-loss injections, also known as GLP-1 receptor agonists, work by mimicking the natural hormone which regulates blood sugar, appetite and digestion – leading to a decreased calorie intake and, as a result, weight loss.
However, drugs such as Mounjaro and Wegovy not only cause rapid fat loss but lean muscle loss too.
Losing this muscle can not only have a significant impact on a person’s overall strength, but fat tissue burns less fat than muscle and a greater lean muscle mass is linked to a lower risk of type 2 diabetes.
Dr Brendan Gabriel, senior lecturer at the Rowett Institute of Nutrition and Health at the University of Aberdeen, who was not involved in the study, said: “Skeletal muscle is a critical tissue for long-term health. Not only is it necessary for enabling movement and preventing frailty as we age, but it also stores the majority of sugar after we eat, meaning it is a key tissue in preventing diabetes and cardiovascular disease.
“Recent advances in obesity therapies are extremely effective at reducing fat mass. But a substantial portion of weight loss during treatment comes from lean mass, including skeletal muscle.”
Although strength training exercises have been shown to limit muscle mass loss that accompanies significant weight loss, researchers found the use of a monoclonal antibody (a lab-made protein) called apitegromab can help retain lean body mass when taking tirzepatide – the drug found in Mounjaro.
Apitegromab works by blocking myostatin, a protein involved in inhibiting muscle growth.
For the study published in the journal Nature Medicine, researchers in the US divided 102 participants into two groups. One group was given apitegromab alongside tirzepatide, and the other was given a placebo with tirzepatide.
After 24 weeks, total weight loss was similar in both groups, but participants given apitegromab alongside tirzepatide lost on average 1.6kg of lean mass while those given tirzepatide alongside a placebo lost about 3.5kg of lean mass.
However, the study authors highlighted there were some limitations. Most of the participants were women, and the study was small and short.
Experts now say larger and longer trials are needed to test the benefits and safety of the drug.
“Strategies that help preserve lean mass while maintaining the benefits of weight reduction are of considerable interest, but whether they improve longer-term health outcomes remains to be established,” said Dr Marie Spreckley, who works in prevention of diabetes and related metabolic disorders in high-risk groups at the University of Cambridge.
“Preserving lean mass is biologically plausible and potentially beneficial, but larger and longer studies will be needed to determine whether these changes translate into meaningful improvements in strength, physical function, quality of life, or long-term health outcomes.”
