TOPLINE:

Both bariatric surgery and treatment with GLP‑1 receptor agonists were associated with reductions in fat mass over 2 years of follow-up. Although both interventions were linked to reductions in fat-free mass, patients who underwent surgery maintained a higher ratio of fat-free mass to fat mass throughout the follow-up period.

METHODOLOGY:

• Obesity treatments such as bariatric surgery and newer GLP-1 receptor agonists have shown substantial benefits in weight loss. Yet, longitudinal clinical data on how they affect body composition are limited.
• Researchers conducted a retrospective cohort study at a US academic medical center to examine 24-month changes in body composition after either bariatric surgery or treatment with GLP-1 drugs (semaglutide or tirzepatide).
• They included adults aged 18-65 years who underwent first-time bariatric surgery between November 2017 and July 2022 (58.4% Roux-en-Y gastric bypass and 41.6% sleeve gastrectomy) or started semaglutide or tirzepatide between November 2018 and December 2023.
• Body composition was measured using bioelectrical impedance analysis at baseline and follow-up visits.
• The primary outcomes were percentage changes in fat mass and fat-free mass and the ratio of fat-free mass to fat mass over a follow-up duration of 24 months.

TAKEAWAY:

• The analysis included 1257 patients in the bariatric surgery group (mean age, 43.4 years; 82.2% women) and 1809 patients in the GLP-1 group (mean age, 45.4 years; 80.5% women). The mean BMI values at baseline were 46.8 and 41.0, respectively.
• The surgery group had an adjusted mean relative reduction in fat mass of 42.4% at 6 months, and 49.7% at 12 months, and 49.7% at 24 months. The corresponding reductions in the GLP-1 group were 10.3%, 17.3%, and 18.0%.
• The adjusted mean relative reduction in fat-free mass in the surgery group was 7.8% at 6 months, 10.6% at 12 months, and 11.7% at 24 months. The corresponding reductions in the GLP-1 group were 1.8%, 3.0%, and 3.3%. The reductions were significant in women.
• The ratio of fat-free mass to fat mass increased in both groups but remained higher after surgery (surgery group: 1.8 at 6 months, 2.1 at 12 months, and 2.0 at 24 months; GLP-1 group: 1.4 at 6 months, 1.5 at 12 months, and 1.5 at 24 months).

IN PRACTICE:

“[The] findings indicate a favorable shift in body composition after surgical or medical weight loss, providing evidence to inform clinical obesity care and interventions aimed at preserving FFM [fat-free mass] while promoting fat loss during obesity treatment,” the authors wrote.

SOURCE:

This study was led by Zicheng Wang, MS, Vanderbilt University Medical Center in Nashville, Tennessee. It was published online in January 2025, in JAMA Network Open.

LIMITATIONS:

Body composition was measured using bioelectrical impedance analysis, which may be less precise than other measures and could be affected by hydration or recent food and activity. The dose or adherence of GLP-1 medicines was not assessed. The retrospective design may have introduced selection bias and unmeasured confounding.

DISCLOSURES:

This study received support from the National Institutes of Health and the National Center for Advancing Translational Sciences Clinical Translational Science Award Program. One author reported receiving personal fees from Intuitive Surgical. Another author reported receiving advisory fees and grants from various pharmaceutical and diagnostic companies including Novo Nordisk, Eli Lilly, Quest Diagnostics, and Rhythm.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.