A new study from Vanderbilt Health shows that both modern weight loss drugs and bariatric surgery (weight loss) can improve body composition in obese patients. These treatments lead to significant fat loss, but also slightly less loss of lean mass (including lean muscle).
This balance is important because body composition plays a huge role in long-term health. The higher the percentage of fat mass (FM), the higher the risk of death from obesity-related diseases such as cardiovascular disease. In contrast, the higher the percentage of fat-free mass (FFM), the lower the risk of death.
Why fat loss and muscle maintenance are important
The findings highlight important trade-offs. Losing fat is beneficial, but maintaining lean body mass is also important for overall health and survival. Understanding how these two components change with different treatments remains an active area of research.
The researchers noted that further research is needed to better understand how FM and FFM change after bariatric surgery and treatment with GLP-1 receptor agonists in real-world clinical settings. Their discovery is JAMA network open.
Study design and patient data
The study was led by Dr. Danxia Yu, associate professor of medicine in the Department of Epidemiology, and Jason Samuels, MD, assistant professor of surgery.
Researchers conducted a retrospective analysis using electronic medical records. The study included 1,257 patients between the ages of 18 and 65 who underwent bariatric surgery at Vanderbilt Health between 2017 and 2022. Also included were 1,809 patients treated with the drugs semaglutide or tirzepatide between 2018 and 2023.
Individuals with a history of end-stage renal disease or congestive heart failure were excluded from the analysis.
To assess changes in body composition, the researchers used bioelectrical impedance analysis. This method estimates FM and FFM based on individual characteristics such as height, weight, age, race, gender, history of diabetes, and duration of GLP-1 treatment.
Key findings over 24 months
Over a 24-month period, both treatment approaches produced similar patterns. Patients had a significant decrease in FM with a slight decrease in FFM. At the same time, the ratio of FFM to FM increased, indicating an overall improvement in body composition.
The study also found differences between men and women. Male patients tended to maintain lean mass more effectively over time than female patients.
Research team and funding
The study’s first authors are graduate student Zicheng Wang, MSc, and postdoctoral researcher Lei Wang, PhD, both of whom specialize in epidemiology.
Additional contributors include Xinmeng Zhang and Dr. You Chen (Biomedical Informatics and Computer Science). Brandon Lowery (Vanderbilt Clinical and Translational Research Institute); Lauren Lee Shafer, MD, and Quinn Wells, MD (Cardiovascular Medicine). Dr. Charles Flynn, Brandon Williams, MD, Matthew Spann, MD, and Gitanjali Srivastava, MD (Surgery).
This research was supported in part by National Institutes of Health grants R01DK126721 and R01CA275864.
