Body Composition Changes After Bariatric Surgery or Treatment With GLP-1 Receptor Agonists
Authors' conclusion
In this single-center cohort study, both bariatric surgery and semaglutide or tirzepatide treatment were associated with substantial FM loss, moderate FFM loss, and improved FFM to FM ratio. These findings provide evidence to guide interventions aimed at preserving FFM while promoting fat loss.
Study context
- Population
- Patients aged 18 to 65 years at Vanderbilt University Medical Center with ≥2 bioelectrical impedance analysis measures, no end-stage kidney disease or congestive HF
- Participants
- 3,066 patients
- Exposure
- Bariatric surgery vs GLP-1 RA
- Surgeryn = 1,257
- GLP-1RAn = 1,809
- Outcome
- Relative changes in FFM, FM and FFM to FM ratio, adjusted for age, sex, race, baseline BMI, diabetes history, treatment year and time
- Follow-up
- Over 24 months
Methodological detailssingle-center, electronic health records
- Single-center
- Electronic health records
Main finding
As reported in the abstract
Adjusted mean relative FM reduction
- Surgery, 6 months
- 42.4% (95% CI, 41.5%-43.2%)
- Surgery, 12 months
- 49.7% (95% CI, 48.8%-50.6%)
- Surgery, 24 months
- 49.7% (95% CI, 47.8%-51.5%)
- GLP-1RA, 6 months
- 10.3% (95% CI, 9.5%-11.0%)
- GLP-1RA, 12 months
- 17.3% (95% CI, 16.5%-18.1%)
- GLP-1RA, third time point (printed as 12 months)
- 18.0% (95% CI, 16.4%-19.7%)
Observational data: associations, not effects.
Further findings
Adjusted mean relative fat-free mass (FFM) reduction
- Surgery, 6 months
- 7.8% (95% CI, 7.2%-8.4%)
- Surgery, 12 months
- 10.6% (95% CI, 10.0%-11.2%)
- Surgery, 24 months
- 11.7% (95% CI, 10.4%-12.9%)
- GLP-1RA, 6 months
- 1.8% (95% CI, 1.3%-2.4%)
- GLP-1RA, 12 months
- 3.0% (95% CI, 2.4%-3.5%)
- GLP-1RA, 24 months
- 3.3% (95% CI, 2.1%-4.4%)
- Primary outcome (one of three)
FFM to fat mass (FM) ratio
- Surgery, 6 months
- 1.8 (95% CI, 1.8-1.8)
- Surgery, 12 months
- 2.1 (95% CI, 2.1-2.1)
- Surgery, 24 months
- 2.0 (95% CI, 2.0-2.1)
- GLP-1RA, 6 months
- 1.4 (95% CI, 1.4-1.4)
- GLP-1RA, 12 months
- 1.5 (95% CI, 1.4-1.5)
- GLP-1RA, 24 months
- 1.5 (95% CI, 1.5-1.6)
- Increased significantly in both groups; surgery maintained a higher ratio throughout
- Primary outcome (one of three)
Stratified analyses (sex, race, baseline body mass index (BMI), diabetes, GLP-1RA duration)
- Similar trends; men showed better FFM preservation than women, especially after GLP-1RA
Original publication
Body Composition Changes After Bariatric Surgery or Treatment With GLP-1 Receptor Agonists. JAMA Netw Open. Published 2 January 2026. doi:10.
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