How much of the weight lost was lean mass?
10.9% lean-mass reductionSURMOUNT-1 DXA substudy: 124 tirzepatide and 36 placebo participants; 72 weeks.
At 72 weeks, fat mass fell 33.9% and lean mass 10.9% with pooled tirzepatide doses, versus 8.2% and 2.6% with placebo. About a quarter of the weight lost was lean mass in both groups.
Both fat and lean mass declined. These results do not establish muscle preservation.
The proportion of weight loss attributed to lean mass differs from the percentage of starting lean mass lost.
What might this mean, and what would change the interpretation?
DXA lean mass is not a direct measure of contractile muscle or strength. This was a 160-person substudy, not the full randomized population.
What would clarify this: Muscle function, regional muscle measures and longer-term follow-up.
Findings reviewed · abstract
Checked Sep 15, 2026 against the linked abstract. This reading note is not a formal risk-of-bias appraisal.
The source links a published correction (DOI 10.1111/dom.70050). Correction text was unavailable in this review; values here are from the current abstract.