Mechanisms of Weight Loss: Tirzepatide vs Semaglutide

The goal of this clinical trial is to determine if there are differences in the effect of 12 weeks of tirzepatide versus semaglutide on energy balance in adults with obesity and without known diabetes. The main questions it aims to answer are: \- Does tirzepatide have a greater effect on energy expenditure or energy extraction than semaglutide? Participants will: * Take tirzepatide or semaglutide once weekly for 12 weeks * Undergo identical baseline and week 12 study visits (including 24-hour whole room indirect calorimeter testing, MRI scan, body composition, 3-day meal plan and stool collection)