Patients using popular weight loss drugs and those undergoing bariatric surgery experience nearly identical changes to their body composition, according to a study published in JAMA Network Open. Researchers at Vanderbilt University Medical Center found that while these treatments successfully reduce fat, they simultaneously trigger a decline in muscle mass.
The study, led by Dr. Danxia Yu and Dr. Jason Samuels, analyzed electronic health records from over 3,000 patients treated between 2017 and 2023. The data compared 1,257 bariatric surgery patients against 1,809 individuals treated with GLP-1 receptor agonists, such as semaglutide and tirzepatide.
Balancing fat loss with muscle health
Maintaining lean muscle is essential for long-term health and protection against early death, even as patients shed excess fat. While the study results indicate an overall improvement in body composition—defined by a higher ratio of lean mass to fat mass—the depletion of muscle remains a clinical concern.
Researchers utilized bioelectrical impedance analysis to track these changes over 24 months. The findings showed that both medical and surgical interventions consistently resulted in substantial fat loss accompanied by a smaller, yet consistent, reduction in fat-free mass.
The data also revealed a disparity between genders. Male patients demonstrated a higher capacity to preserve fat-free mass throughout their treatment compared to their female counterparts.
Dr. Yu and Dr. Samuels emphasized that these findings provide a clearer picture of how modern obesity treatments function in real-world clinical settings. They noted that further research is required to understand the long-term health consequences of this specific shift in body composition. The study was supported by grants from the National Institutes of Health.
