GLP-1, myostatin and the quality of weight loss
Can Muscle Be Preserved During GLP-1 Weight Loss? What the Trevogrumab Trial Actually Found
Preserving muscle during weight loss is clinically important, particularly after 40 and for people who already have low muscle mass. Trevogrumab reduced imaging-based losses in a phase 2 trial, but lean mass, muscle and function are not interchangeable—and that distinction changes the conclusion.
Why the question matters
Some of the weight lost during obesity treatment comes from fat-free mass. That category includes muscle, but also water, organs and other tissues. The clinical meaning depends on who is losing it, how much is lost, strength and physical function—not only a number from a scale or body-composition test.
What trevogrumab is
Trevogrumab is an investigational monoclonal antibody that blocks myostatin, a protein that restrains muscle growth. COURAGE studied it with semaglutide 2.4 mg in adults with obesity. No regulatory authority has approved the medicine to preserve muscle during weight loss.
The 52-week comparison
In the lower-dose portion, participants received semaglutide with placebo, trevogrumab 25 mg or trevogrumab 75 mg. Dual-energy X-ray absorptiometry, or DXA, showed lean-mass losses of 7.3% with semaglutide alone, 5.8% with 25 mg and 4.2% with 75 mg. This represented relative preservation of 20.5% and 42.5%, respectively.
MRI measured something closer to muscle
A prespecified substudy used magnetic resonance imaging to measure fat-free thigh-muscle volume. At 52 weeks, trevogrumab preserved about 71.8% of this volume with 25 mg and 68.9% with 75 mg relative to the loss seen with semaglutide alone. The finding is promising, but it comes from a subset and does not represent every muscle in the body.
Preserving an image is not proof of preserving function
Neither DXA nor muscle volume alone tells us whether a person became stronger, walked better, maintained independence or reduced falls. Those outcomes matter most, particularly in older or frail adults. The trial supports an effect on body measurements; it has not yet established sufficient functional benefit.
People with low lean mass may require particular attention
A prespecified analysis suggested greater lean-mass loss with semaglutide alone and numerically greater preservation with trevogrumab among participants who started with low lean mass. This helps define the next research question, but it cannot yet be extrapolated to clinical sarcopenia, frail older adults or disability prevention.
Safety and independence of the evidence
At the lower doses, 77% of participants receiving trevogrumab and 82% receiving placebo reported at least one adverse event; nausea, constipation, diarrhoea and vomiting were the most common. The manufacturer sponsored the trial. Results were presented at a congress and reported as accepted for publication, but complete peer-reviewed assessment remained limited when this article was prepared.
The medicine would not replace protein and resistance training
Even if future research confirms clinical benefit, blocking myostatin would not make adequate nutrition, sufficient protein, resistance exercise and follow-up unnecessary. These strategies have broader effects on strength, cardiorespiratory capacity, bone, metabolism and behaviour. Care should be adapted to reduced intake, symptoms, age, training and muscle-loss risk.
What can be concluded today
Trevogrumab suggests that it may be biologically possible to alter the composition of weight lost with a GLP-1 receptor agonist. Evidence is still needed for strength, mobility, quality of life, long-term safety and people who are older or have sarcopenia. For now, it is promising research—not an available treatment.
Personalized care
A plan should fit the person, not the trend.
Scientific references
This page is educational and does not replace individual medical or nutrition assessment.