The Study
GDF8 and activin A blockade protects against GLP-1–induced muscle loss while enhancing fat loss in obese male mice and non-human primates
This study looked at how a special treatment affected the bodies of male mice and monkeys, and found that they lost more fat and kept more muscle when given the treatment. But it didn't randomly assign animals to groups or hide which animals got the treatment, so we can't be sure the treatment caused the changes — maybe something else did.
Analysis score
Maximum 90 for a randomized controlled trial.
Where the score came from
Weight-loss drugs like semaglutide make you lose muscle along with fat. This study tried a new combo treatment that blocks two natural signals that tell your body to shrink muscles.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 514 / 100
Quality score
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
Key takeaways
Summary
Based on the study abstract and findings.
- 1Yes—preserving muscle while losing more fat could make weight loss healthier and more sustainable, reducing rebound weight gain and metabolic risks.
- 2In mice, the combo lost twice as much fat as semaglutide alone.
- 3In monkeys, it built more muscle and lost more fat over 20 weeks, while also improving blood sugar and cholesterol.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
Nature Communications
Year
2025
Authors
Jason W. Mastaitis, Daniel Gomez, J. Raya, Diana Li, Soo Min, Michael Stec, Sandra Kleiner, Toya McWilliams, Judith Y. Altarejos, Andrew J. Murphy, G. Yancopoulos, Mark W. Sleeman
Related Content
Claims (5)
To lose body fat, you must consume fewer calories than you expend, and the size of this calorie deficit has a greater impact on fat loss than whether you do running, weightlifting, or other forms of exercise.
In obese male primates, combining a drug that blocks two specific muscle-regulating proteins with semaglutide leads to greater increases in muscle mass and more fat loss than semaglutide alone, along with improved blood sugar and cholesterol levels after 20 weeks of treatment.
In obese male primates, combining a treatment that blocks two specific proteins (GDF8 and activin A) with GLP-1 therapy leads to larger improvements in blood sugar control and cholesterol levels than GLP-1 therapy by itself.
In obese male mice and non-human primates, blocking two specific proteins (GDF8 and activin A) while using a GLP-1 receptor agonist helps maintain or increase muscle mass and enhances fat loss, leading to better body composition and improved metabolic indicators like lower liver fat and healthier blood lipids.
In obese male mice, combining semaglutide with a treatment that blocks GDF8 and activin A leads to about twice as much fat loss over four weeks compared to semaglutide alone, even when total weight loss is the same, indicating that preserving muscle may help the body remove more fat.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.