Greater lean-body-mass decline with tirzepatide than semaglutide in routine care, revealed by body-composition digital phenotyping
This large-scale observational study used an EHR-linked body-composition "digital phenotyping" pipeline — incorporating large language model (LLM)-based data extraction — to compare lean body mass (LBM) changes in routine clinical care among adults initiating GLP-1 receptor agonists (GLP-1RAs). Of 670,422 first-episode GLP-1RA users (456,742 on semaglutide; 213,680 on tirzepatide), 7,965 had paired pre- and post-initiation body-composition measurements analyzable over 12 months. The study found that tirzepatide was associated with greater relative LBM loss than semaglutide at each time point assessed (3, 6, 9, and 12 months), with excess LBM losses ranging from approximately 1.1% to 2.0%. The authors also identified two GLP-1 "metabotypes": a "Depletive" metabotype (>20% total body weight loss with >5% LBM loss), which was more frequent with tirzepatide (10.3%) than semaglutide (6.7%), and a "Prime" metabotype (>10% total body weight loss with preserved LBM). Key limitations include the observational, real-world design; reliance on LLM-extracted EHR data; potential unmeasured confounding; and the relatively small subset with paired body-composition data relative to the overall cohort.
Why this grade: Although the human sample is large, this is an uncontrolled retrospective observational preprint relying on LLM-extracted EHR data with a small proportion of participants having paired body-composition measurements, limiting causal inference.
Abstract GLP-1 receptor agonists induce substantial weight loss, but the extent to which lean tissue and physical function are preserved in routine care remains poorly understood. Using an EHR-linked body-composition digital phenotyping pipeline with LLM-based extraction, we performed a large-scale longitudinal analysis of 670,422 first-episode GLP-1RA users, including 456,742 treated with semaglutide and 213,680 treated with tirzepatide. Among these, 7,965 individuals with paired pre- and post-initiation body-composition measurements were analyzed over 12 months. Tirzepatide was associated with greater relative lean body mass (LBM) loss than semaglutide at each measured time point, with excess LBM losses of 1.1%, 1.5%, 1.3% and 2% at 3, 6, 9 and 12 months, respectively. A Depletive GLP-1 metabotype , defined as > 20% total body weight (TBW) loss with > 5% LBM loss, was significantly more frequent with tirzepatide than semaglutide during the first year of therapy (10.3% versus 6.7%, p Prime GLP-1 metabotype , defined as > 10% TBW loss with Prime GLP-1 metabotype .
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