This prospective cohort study investigates the effects of tirzepatide versus liraglutide on bone turnover markers and body composition in adults with class 3 obesity, characterised by Body Mass Index (BMI) ≥40 kg/m². Participants will be followed for 6 months with assessments at baseline, 3 and 6. The primary outcome is the change in bone resorption marker C-terminal telopeptide of type I collagen (CTX) at 3 months. Secondary outcomes include changes in body weight, BMI, bone mineral density (BMD), and body composition. The study aims to clarify the differential impact of weight loss achieved through tirzepatide versus liraglutide on bone metabolism and body composition in adults with obesity.