236-OR: Short-Term Effects of Semaglutide and Tirzepatide on Body Composition in Patients with Obesity Undergoing a Low-Calorie Diet

Objective: Severe caloric restriction, used for preoperative short-term weight loss, can lead to muscle loss, subsequently worsen glucose tolerance and cause weight regain. This observational study explored the short-term effects of semaglutide (SEMA) and tirzepatide (TZP) on weight loss and body composition in patients with obesity during a 13-day-low-calorie diet.

Methods: Japanese adults with a body mass index ≥ 25 kg/m² who completed our hospital’s diet (800 kcal/day) and exercise therapy between 2019 and 2023 were included. Those who started oral or injectable SEMA or TZP upon admission, and those without a history of glucagon-like peptide-1 (GLP-1) receptor agonists or TZP use, were assigned to the GLP-1 (n = 28) and FREE groups (n = 19), respectively. Changes in body weight and body composition, measured by bioelectrical impedance analysis, before and after hospitalization were compared between the groups using Student t-test and analysis of covariance, respectively.

Results: Significant weight loss occurred in both groups, but no significant difference was observed between them (-4.34% with GLP-1 group vs. -4.63% with FREE group; estimated treatment difference, -0.28%; 95% confidence interval (CI), -1.06 to 0.49; p = 0.464). Fat mass decreased in the GLP-1 group (-10.10% with GLP-1 group vs. -1.93% with FREE group; estimated treatment difference, -8.17%; 95% CI, -1.42 to -14.92; p = 0.019), whereas fat-free mass decreased in the FREE group (0.98% with GLP-1 group vs. -4.58% with FREE group; estimated treatment difference, 5.56%; 95% CI, 0.03 to 0.75; p = 0.025). Analysis within the GLP-1 group suggested a greater body composition improvement with TZP than with SEMA.

Conclusion: A 13-day treatment with SEMA or TZP improves body composition in patients with obesity undergoing severe caloric restriction, with TZP demonstrating a more substantial effect.