Summary: In a SURMOUNT-1 post-hoc analysis in people with obesity but without diabetes, tirzepatide improved both insulin sensitivity and beta-cell function over 72 weeks, with the sensitivity gain driven mostly by weight loss and the beta-cell improvement driven mostly by the drug itself.
PICO Summary
| Element | Detail |
|---|---|
| Population | 2539 adults with BMI ≥27 and prediabetes or normoglycaemia (no type 2 diabetes) in SURMOUNT-1. |
| Intervention | Tirzepatide once weekly for 72 weeks, with beta-cell function and insulin sensitivity modelled from oral glucose tolerance tests. |
| Comparison | Placebo. |
| Outcome | Tirzepatide improved insulin sensitivity and beta-cell function overall and in both prediabetes and normoglycaemia. In regression models, the insulin-sensitivity gain was associated mostly with weight reduction, whereas the beta-cell function gain was associated mostly with tirzepatide treatment, i.e. partly independent of weight loss. |
Expert Commentary
This is an elegant mechanistic dissection, and its most interesting contribution is not that tirzepatide improves insulin sensitivity and beta-cell function, which one would expect, but the attempt to separate why. The modelling suggests a genuine division of labour: improved insulin sensitivity tracked mainly with weight loss, the obvious downstream benefit of shedding adiposity, while the enhancement in beta-cell function tracked mainly with the drug itself, hinting at a direct islet effect of dual GIP/GLP-1 agonism beyond mere weight reduction. That distinction matters for how we think about these agents preventing progression to diabetes in people who currently have none. The caveats are appropriate: this is a post-hoc analysis using model-derived indices from glucose tolerance tests rather than gold-standard clamp or hard diabetes-incidence endpoints, and statistical attribution of mechanism is always softer than it looks. Can I use this with my patients? Supportively. For a patient with obesity and prediabetes, it strengthens the rationale that tirzepatide does more than help them lose weight, it may directly improve the insulin-secreting capacity that determines whether they tip into diabetes. The outcome trials, not this analysis, remain the basis for that claim.
References
Mari A, Stefanski A, van Raalte DH, et al. Tirzepatide treatment and associated changes in β-cell function and insulin sensitivity in people with obesity or overweight with prediabetes or normoglycemia: a post hoc analysis from the SURMOUNT-1 trial. Diabetes Care. 2025;48(9):1622–1627. doi:10.2337/dc25-0763