Effects of 6-month treatment with the GLP-1 receptor agonist liraglutide on 24-hour energy metabolism and body composition in adults with obesity

Purpose Glucagon-like peptide 1 receptor agonists (GLP-1 RAs) are effective drugs for weight loss and management of obesity-related comorbidities. Their role in 24-hour energy metabolism remains unclear. This study evaluated the effect of liraglutide treatment on 24-hour energy metabolism and body composition in a real-life clinical setting. Methods This prospective study enrolled 11 patients with obesity (8 females; mean age 49 ± 9 years; weight 103 ± 18 kg) treated with liraglutide for 6 months at clinically titrated doses at the Obesity and Lipodystrophy Center, University Hospital of Pisa. Measurements of 24-hour energy expenditure (24hEE), 24-hour sleeping metabolic rate (24hSMR), and substrate oxidation (carbohydrates, lipids, proteins) were obtained via whole-room indirect calorimetry prior to start the therapy (V1) and after 6 months (V2). Body composition was assessed by Dual-Energy X-ray Absorptiometry (DXA) at V1 and V2. Results At V2, participants showed significant weight loss (− 10.5 kg, p < 0.001), primarily driven by a decrease in total fat mass (− 8.7 kg, p < 0.001), with a marked reduction in trunk fat mass (− 5.1 kg, p < 0.001). A modest yet statistically significant reduction in total lean soft tissue was also observed (− 1.7 kg, p = 0.02). No changes in 24hEE and 24hSMR could be detected. Fat oxidation increased (+ 352 kcal/d, p = 0.03), while carbohydrate oxidation decreased (− 422 kcal/d, p = 0.003), and protein oxidation remained stable. Conclusion Liraglutide induces significant weight loss in patients with obesity, primarily through fat mass reduction, while largely preserving lean soft tissue. These changes are accompanied by a shift toward fat oxidation, without relevant variations in 24hEE.