Bariatric Surgery Produces Greater Fat Loss and More Favorable Body Composition Than GLP-1 Therapy: JAMA
USA: Researchers have found in a new study that, over two years, bariatric surgery resulted in substantially greater fat-mass reduction compared with GLP-1 receptor agonist therapy. Surgery also led to a higher fat-free mass–to–fat-mass ratio, indicating relatively greater preservation of muscle, bone, and body water.
Researchers have noted that a higher fat-free mass-to-fat-mass ratio may be associated with a reduced mortality risk, suggesting that bariatric surgery offers more favorable body composition benefits than GLP-1 medications.
The findings are from a large real-world analysis published in JAMA Network Open by Zicheng Wang from the Division of Epidemiology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee, and colleagues. The study compared changes in body composition among patients who underwent bariatric surgery with those treated using newer glucagon-like peptide-1 receptor agonists (GLP-1RAs), specifically semaglutide and tirzepatide, over 24 months.
While both bariatric surgery and GLP-1RA therapy are known to induce weight loss, evidence comparing their effects on fat mass and fat-free mass in routine clinical practice has been limited. To address this gap, the researchers examined electronic health record data from a single academic medical center, focusing on changes in fat mass, fat-free mass, and the ratio between the two over time.
The retrospective cohort study included 3,066 adults aged 18 to 65 years. Of these, 1,257 patients underwent first-time bariatric surgery between 2017 and 2022 and had not used GLP-1RAs before or after surgery. The remaining 1,809 patients were treated with semaglutide or tirzepatide between 2018 and 2023. All participants had at least two bioelectrical impedance analysis measurements and no history of end-stage kidney disease or congestive heart failure.
The study led to the following findings:
- After adjustment for age, sex, race, baseline BMI, diabetes history, and treatment timing, clear differences in body composition changes were observed between bariatric surgery and GLP-1RA treatment groups.
- Bariatric surgery was associated with marked reductions in fat mass, with nearly 50% loss achieved by 12 months and maintained through 24 months.
- GLP-1 receptor agonist therapy resulted in more modest fat mass reductions over the same follow-up period.
- Both treatment groups experienced some decline in fat-free mass, including muscle and other lean tissues.
- Fat-free mass loss was relatively small compared with fat mass loss, particularly among patients who underwent bariatric surgery.
- The fat-free mass–to–fat-mass ratio increased significantly in both groups, reflecting an overall improvement in body composition.
- Surgical patients consistently maintained a higher fat-free mass–to–fat-mass ratio at all time points compared with those receiving GLP-1RA therapy.
- Subgroup analyses demonstrated that these patterns were largely consistent across sex, race, baseline BMI, diabetes status, and treatment duration.
- Men showed better preservation of fat-free mass than women, especially among patients treated with GLP-1 receptor agonists.
Overall, the study suggests that while both bariatric surgery and GLP-1 receptor agonists are effective tools for reducing fat mass over two years, bariatric surgery is associated with a more favorable shift in body composition. The authors noted that these findings may help clinicians tailor obesity treatments with a focus not only on weight loss, but also on preserving lean mass and improving long-term health outcomes.
Reference:
Wang Z, Wang L, Zhang X, et al. Body Composition Changes After Bariatric Surgery or Treatment With GLP-1 Receptor Agonists. JAMA Netw Open. 2026;9(1):e2553323. doi:10.1001/jamanetworkopen.2025.53323
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