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.