Bariatric surgery, GLP1-RAs effectively reduce fat mass in obese adults

Among adults with obesity, either bariatric surgery or glucagon-like peptide 1 receptor agonists (GLP-1 RAs), such as semaglutide or tirzepatide, led to substantial fat mass (FM) loss and moderate fat-free mass (FFM) loss, according to a recent study.

“Bariatric surgery and GLP-1 RA medications are currently the most effective weight-loss interventions for people with obesity, especially those with severe obesity and comorbidities,” said the researchers.

“Growing evidence suggests that FM and FFM may have distinct and often opposing effects on mortality. Therefore, it is important to monitor changes in FM and FFM during obesity treatment, aiming to reduce FM while preserving FFM,” they noted.

Hence, the researchers conducted a retrospective cohort study involving 3,066 obese patients, of whom 1,257 (mean age 43.4 years) had bariatric surgery (Roux-en-Y gastric bypass [n=734] or sleeve gastrectomy [n=523]) and 1,809 (mean age 45.4 years) received GLP-1 RAs (semaglutide [n=1,646] or tirzepatide [n=163]). Mean BMIs were 46.8 and 41 kg/m² at baseline, respectively. [JAMA Netw Open 2026;doi:10.1001/jamanetworkopen.2025.53323]

Following treatment, the adjusted mean relative FM reductions were 42.4 percent at 6 months and 49.7 percent at both 12 and 24 months in the surgery group, whereas the GLP-1 RA group showed reductions of 10.3 percent, 17.3 percent, and 18 percent at the corresponding time points.

Similarly, adjusted mean FFM were greatly reduced by 7.8 percent at 6 months, 10.6 percent at 12 months, and 11.7 percent at 24 months in the surgery group compared with 1.8 percent, 3 percent, and 3.3 percent, respectively, in the GLP-1 RA group.

“After both treatments, FM decreased significantly over time, with the patients in the surgery group showing a more marked FM reduction than those in the GLP-1 RA group,” said the researchers.

The mean FFM to FM ratio improved significantly from baseline to 24 months in both the surgery (from 1 to 2) and GLP-1 RA (from 1.2 to 1.5) groups, but with the surgery group consistently maintained a higher ratio throughout the 24-month treatment period, the researchers noted.

Across all patient subgroups, including sex, race, baseline BMI, diabetes history, and GLP-1 RA treatment duration, a similar trend of significant reductions in FM and increases in the FFM to FM ratio was observed in both surgical and nonsurgical groups.

However, males showed better FFM preservation than females, especially after GLP-1 RA treatment, the researchers noted.

“This study suggests that both bariatric surgery and newer GLP-1 RAs were associated with significant reductions in FM, modest reductions in FFM, and an increase in the FFM to FM ratio over 24 months,” said the researchers.