Retatrutide Slashed Body Fat by Up to 26% in Type 2 Diabetes — and Didn't Lose More Muscle Than Other Drugs
In a phase 2 substudy using DXA scans, retatrutide 8 mg reduced total body fat mass by 26.1% over 36 weeks in people with type 2 diabetes, significantly outperforming both placebo and dulaglutide without disproportionate lean mass loss.
Quick Facts
What This Study Found
Fat mass reduction from baseline at 36 weeks was dose-dependent: 4.9% with retatrutide 0.5 mg, 15.2% with 4 mg, 26.1% with 8 mg, and 23.2% with 12 mg, compared to 4.5% for placebo and 2.6% for dulaglutide. Versus placebo, the 8 mg dose achieved a 21.6 percentage point greater fat reduction (p<0.0001). The 12 mg dose showed slightly less fat loss than 8 mg, though both were highly significant versus placebo.
Importantly, the proportion of lean mass loss relative to total weight loss was comparable to other obesity treatments, providing reassurance that retatrutide's superior weight loss doesn't come with disproportionate muscle loss. Adverse events were mainly gastrointestinal and similar across groups.
Key Numbers
How They Did This
Phase 2, double-blind, placebo-controlled, randomized substudy across 42 US medical centers. 189 adults with type 2 diabetes (BMI 25-50 kg/m²) were enrolled in the body composition substudy. Body composition was measured by dual-energy X-ray absorptiometry (DXA) at baseline and week 36. Participants received once-weekly subcutaneous injections of placebo, dulaglutide 1.5 mg, or retatrutide at various doses (0.5–12 mg). 103 participants completed both DXA scans.
Why This Research Matters
A major concern with GLP-1-class weight loss drugs is that people lose muscle along with fat — so-called 'Ozempic butt' and sarcopenia concerns. This study shows that retatrutide, despite producing more dramatic fat loss than single-target GLP-1 drugs, doesn't cause proportionally more muscle loss. This is critical data because retatrutide adds glucagon receptor agonism (which may promote fat oxidation specifically) and could represent the next generation of obesity treatment.
The Bigger Picture
Retatrutide represents the cutting edge of incretin-based obesity drugs: a triple agonist targeting GLP-1, GIP, and glucagon receptors. This body composition data is pivotal because it addresses the biggest criticism of weight loss drugs — that they burn muscle along with fat. By showing that the lean mass to total weight loss ratio is preserved even at extreme fat loss levels, this study de-risks one of the main concerns about the next generation of multi-receptor agonists. Phase 3 trials (TRIUMPH program) are ongoing.
What This Study Doesn't Tell Us
Only 103 participants completed both DXA scans out of 189 enrolled, representing significant attrition. The 36-week duration may not capture long-term body composition changes. The substudy was not powered as a primary endpoint study. The 12 mg dose showed less fat loss than 8 mg, which is unexpected and may reflect small sample sizes at individual dose levels. Funded by Eli Lilly (retatrutide's manufacturer).
Questions This Raises
- ?Why did the 12 mg dose show slightly less fat loss than 8 mg — is there a ceiling effect, or is this just noise from small sample sizes?
- ?Will resistance exercise combined with retatrutide further preserve lean mass compared to the drug alone?
- ?How does retatrutide's body composition profile compare to tirzepatide (GLP-1/GIP dual agonist) using the same DXA methodology?
Trust & Context
- Key Stat:
- 26.1% fat mass reduction Retatrutide 8 mg reduced total body fat by over a quarter in 36 weeks — far more than placebo (4.5%) or dulaglutide (2.6%) — as confirmed by DXA scanning
- Evidence Grade:
- This is a prespecified substudy of a phase 2 randomized, double-blind, placebo-controlled trial published in The Lancet Diabetes & Endocrinology. The DXA methodology is gold-standard for body composition. However, the substudy had significant attrition (103 of 189 completers) and relatively small group sizes.
- Study Age:
- Published in 2025 with data from a 2021-2022 trial. Retatrutide is currently in phase 3 trials (TRIUMPH program). This body composition data is the most detailed available for any triple-agonist obesity drug.
- Original Title:
- Effects of retatrutide on body composition in people with type 2 diabetes: a substudy of a phase 2, double-blind, parallel-group, placebo-controlled, randomised trial.
- Published In:
- The lancet. Diabetes & endocrinology, 13(8), 674-684 (2025)
- Authors:
- Coskun, Tamer(12), Wu, Qiwei(2), Schloot, Nanette C, Haupt, Axel, Milicevic, Zvonko, Khouli, Courtney, Harris, Charles
- Database ID:
- RPEP-10549
Evidence Hierarchy
Frequently Asked Questions
Does retatrutide cause more muscle loss than other weight loss drugs?
No — that's one of the key findings. Despite reducing body fat by up to 26%, the proportion of lean mass lost relative to total weight lost was similar to other obesity treatments. This means retatrutide's extra weight loss came primarily from fat, not additional muscle, which is reassuring for a drug that produces such dramatic results.
How does retatrutide compare to semaglutide and tirzepatide?
Retatrutide targets three receptors (GLP-1, GIP, and glucagon) compared to semaglutide's one (GLP-1) and tirzepatide's two (GLP-1 + GIP). The glucagon receptor component may promote fat burning specifically. In this study, retatrutide 8 mg reduced fat by 26.1% in 36 weeks — comparable to or exceeding what tirzepatide achieves in longer trials. Direct head-to-head comparisons are still needed.
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Cite This Study
https://rethinkpeptides.com/research/RPEP-10549APA
Coskun, Tamer; Wu, Qiwei; Schloot, Nanette C; Haupt, Axel; Milicevic, Zvonko; Khouli, Courtney; Harris, Charles. (2025). Effects of retatrutide on body composition in people with type 2 diabetes: a substudy of a phase 2, double-blind, parallel-group, placebo-controlled, randomised trial.. The lancet. Diabetes & endocrinology, 13(8), 674-684. https://doi.org/10.1016/S2213-8587(25)00092-0
MLA
Coskun, Tamer, et al. "Effects of retatrutide on body composition in people with type 2 diabetes: a substudy of a phase 2, double-blind, parallel-group, placebo-controlled, randomised trial.." The lancet. Diabetes & endocrinology, 2025. https://doi.org/10.1016/S2213-8587(25)00092-0
RethinkPeptides
RethinkPeptides Research Database. "Effects of retatrutide on body composition in people with ty..." RPEP-10549. Retrieved from https://rethinkpeptides.com/research/coskun-2025-effects-of-retatrutide-on
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Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkPeptides research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.