The Study
GDF8 and activin A are the key negative regulators of muscle mass in postmenopausal females: a randomized phase I trial
This study gave a special medicine to a small group of healthy women and saw that their muscles got bigger and fat got smaller. Because they randomly gave some the medicine and some nothing, we can guess the medicine caused the change—but only in these women, and only for a few months.
Analysis score
Maximum 90 for a randomized controlled trial.
Where the score came from
Scientists gave healthy older women two special antibodies that block two proteins (GDF8 and activin A) that normally keep muscles small and fat high.
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 582 / 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.
- 1A 6% muscle gain is meaningful — it’s like gaining the muscle mass of a small apple in your thigh, without exercise.
- 2Fat loss is also notable, suggesting this could help with obesity or aging-related muscle loss.
- 3After one dose, thigh muscles grew by about 6% and body fat went down.
- 4When they gave the antibodies multiple times, muscles kept growing — but only while the treatment continued.
- 5After stopping, muscles returned to normal.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
Nature Communications
Year
2025
Authors
Dinko Gonzalez Trotter, Stephen Donahue, Chris Wynne, Shazia Ali, Prodromos Parasoglou, Anita Boyapati, K. Mohammadi, Bret J. Musser, Pretty Meier, Jason W. Mastaitis, Mark W. Sleeman, David J. Glass, E. Gasparino, Jesus Trejos, John D Davis, Boaz Hirshberg, R. Pordy, G. Yancopoulos, G. Herman
Related Content
Claims (9)
Myostatin is a protein in the body that reduces the growth of skeletal muscle.
Myostatin-inhibiting antibodies increase muscle mass in animals by blocking biological signals that normally restrict muscle growth.
Bimagrumab, a specific antibody, decreases body fat without requiring the presence or activity of GLP-1 receptor agonists.
In healthy postmenopausal women, injecting antibodies that block GDF8 and activin A for 12 weeks increases thigh muscle volume, and this increase disappears by 28 weeks after stopping the injections.
In healthy postmenopausal women, blocking the proteins GDF8 and activin A with specific antibodies increases muscle mass and decreases fat mass in proportion to the amount of antibody present in the blood.
A single injection of two specific antibodies in healthy postmenopausal women aged 45–70 increases thigh muscle volume by about 6% and reduces total and abdominal fat mass over 8 weeks, demonstrating that GDF8 and activin A are key regulators of human muscle and fat mass.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.