Antibody Helped Patients Retain Lean Mass, Even As Key Health Questions Remain
When people lose weight on GLP-1 medications, they may also lose muscle. But a proof-of-concept drug could help preserve that lean tissue.
When taken at the same time as a powerful weight loss medication, experimental antibody allows patients to maintain lean body massscientists report on June 8 Natural medicine.
The drug has not yet been approved by the U.S. Food and Drug Administration and is available only via intravenous infusions. So it’s not something consumers are likely to get their hands on anytime soon, says study co-author Richard Pratley, a clinician and metabolic disease researcher at the AdventHealth Translational Research Institute in Orlando, Florida. This may be good news for GLP-1 users, but important questions remain.
Scientists don’t know if maintaining lean mass in this way actually translates into better health. They also don’t know the long-term effects or whether these drugs might help people other than GLP-1 users, such as older people whose muscles decline with age. “We need to find out what these drugs are capable of,” Pratley says.
GLP-1 medications can cause drastic and rapid weight loss. But not all the weight lost is fat. About 25 to 40 percent is made up of lean body mass, which includes a person’s muscles, organs and blood. Although patients may lose some muscle when they lose lean mass, it may be less than we think, says Randy Seeley, an obesity researcher at the University of Michigan Medical School in Ann Arbor, who was not involved in the study. Despite what you hear from social media influencers about the importance of maintaining muscle mass when taking Ozempic, he says, for most people, “it’s not a problem that needs to be solved.”
This view is supported by clinical trials of GLP-1 drugs. For most participants, Pratley says, the loss of lean mass doesn’t seem to impact function. “If anything, people tend to become more functional,” he says, “because they can do more things and it’s easier to get around.”
But it’s unclear how data from past clinical trials translates to the broader population of people using weight-loss drugs in real life. There may be people for whom a lean mass-preserving medication could be helpful. In the new study, researchers tested an antibody that inhibits myostatin, a protein that inhibits muscle growth. Removing these brakes should counteract some of the loss of lean mass that accompanies weight loss, the researchers hypothesized.
The drug, apitegromab, has already been tested for another condition, spinal muscular atrophy. For the new study, Pratley’s team tested it in a clinical trial involving 102 people with a body mass index classified as overweight or obese. All participants received weekly injections of tirzepatide, a weight-loss drug, for 24 weeks; half also received a monthly infusion of antibodies. People in both groups lost about the same amount of weight, but those who received the antibody lost half as much lean mass as those who took tirzepatide alone.
The researchers “absolutely demonstrate that they can preserve lean mass,” Seeley says. But for him, the unanswered question is whether this preservation makes sense. There are hints that this might be the case. Participants in the antibody group had slightly better grip strength than their counterparts and performed better on a test measuring leg strength and endurance.
It’s a step in the right direction, Pratley said. But the gains were minor and the number of study participants was small. This is something scientists could explore in future studies, as well as how apitegromab and related drugs work in older and frail people.
The goal is to tailor patients’ medications to their specific needs, Pratley says, finding “the right drug for the right patient at the right time.”
