Obesity is a growing public health concern associated with increased risk of chronic diseases, including type 2 diabetes and cardiovascular disease. Glucagon-like peptide-1 receptor agonists (GLP-1RAs) have become a key therapeutic option for obesity management, yet real-world evidence describing short-term changes in body composition, particularly with newer agents such as tirzepatide, remains limited. This retrospective study examined changes in body weight, body mass index (BMI), and body composition among adults with obesity receiving GLP-1 receptor agonist therapy within a clinical obesity medicine program that included individualized lifestyle guidance. Thirty-five adults (53.4 ± 7.8 years; BMI 37.2 ± 9.16 kg/m²) receiving tirzepatide were evaluated. Therapy was initiated at 2.5 mg or 5 mg once weekly, with scaffolded dose escalation up to 15 mg based on tolerance and clinical response. Body weight was measured using standard procedures, and body composition was assessed with bioelectrical impedance analysis (InBody770) at baseline and follow-up visits. Linear mixed models and ANOVA were used to examine effects of time, sex, and baseline weight status (p < 0.050).GLP-1RA therapy resulted in significant reductions in body weight (-31.1 kg; -27.8%), BMI (-10.4 kg/m²; -27.8%), body fat percentage (-16.2%; -37.6%), fat mass (-26.4 kg; -54.2%), fat-free mass (-4.5 kg; -7.3%), skeletal muscle mass (-2.8 kg; -8.3%), and total body water (-3.5 kg; -7.7%) (all p < 0.001). Weight loss was predominantly attributable to fat mass, comprising 85.7% (95% CI: 81.9, 89.5) of total weight loss, with smaller contributions from fat-free and skeletal muscle mass. Reductions in extracellular (-2.6 kg; -9.5%) and intracellular water (-1.3 kg; -7.4%) were observed; however, fluid distribution indices did not change significantly over time.Sex-specific analyses showed females experienced greater percentage reductions in fat mass, fat-free mass, skeletal muscle mass, and total body water compared to males, while males exhibited greater reductions in fluid ratios (p < 0.05). Participants with higher baseline BMI demonstrated significantly greater percentage reductions in weight, BMI, fat mass, and body fat percentage compared to those with lower baseline BMI (p < 0.05), although post-treatment values were not significantly different between groups.
GLP-1 Therapies