This record provides bibliographic details and links to the original research. An editorial study breakdown is not available.
What the researchers found
In the SURPASS-3 MRI substudy, tirzepatide reduced thigh muscle fat infiltration more than expected from weight loss alone. Muscle volume decreased proportionally to weight loss. Compared to insulin degludec, tirzepatide showed distinct muscle composition changes.
Why it matters
Weight loss drugs raise concerns about muscle loss. This MRI study suggests tirzepatide's muscle volume changes are typical for the amount of weight lost, and it may actually improve muscle quality by reducing fat within muscle tissue.
The numbers in context
246 participants analyzed (190 tirzepatide, 56 insulin degludec). Tirzepatide: muscle fat infiltration decreased 0.36 percentage points (p<0.0001). Muscle volume decreased 0.64 L (p<0.0001). Muscle volume Z score decreased 0.22 (p<0.0001). Muscle volume changes matched population-based estimates for weight loss. Fat infiltration reduction exceeded estimates (difference -0.42 pp, p<0.0001).
How the study worked
Post-hoc analysis of the SURPASS-3 MRI substudy. Phase 3, randomized, open-label trial comparing tirzepatide (5/10/15 mg weekly) vs. insulin degludec. Thigh MRI at baseline and week 52. Compared observed changes to UK Biobank population estimates (n=2942).
Who was studied
Adults with type 2 diabetes, mean age 56 years, BMI 33.4 kg/m2, 60% male, insulin-naive on metformin
What this study cannot tell us
Post-hoc exploratory analysis. Open-label design. MRI substudy subset only. Cannot determine if muscle quality improvement translates to functional benefits. Funded by Eli Lilly.
Read the original research
Tirzepatide and muscle composition changes in people with type 2 diabetes (SURPASS-3 MRI): a post-hoc analysis of a randomised, open-label, parallel-group, phase 3 trial.
The lancet. Diabetes & endocrinology, 13(6), 482-493
Citation
Sattar, Naveed; Neeland, Ian J; Dahlqvist Leinhard, Olof; Fernández Landó, Laura; Bray, Ross; Linge, Jennifer; Rodriguez, Angel. (2025). Tirzepatide and muscle composition changes in people with type 2 diabetes (SURPASS-3 MRI): a post-hoc analysis of a randomised, open-label, parallel-group, phase 3 trial.. The lancet. Diabetes & endocrinology, 13(6), 482-493. https://doi.org/10.1016/S2213-8587(25)00027-0