In a previous study (NCT04081337), 55 participants with obesity participated on a 18-week lifestyle intervention to reduce their body weight, targeting 10% body weight loss. The participants received tirzepatide (15mg after titration) or placebo during the weight loss intervention. Before and after the lifestyle intervention, energy expenditure (48-h room indirect calorimetry) and body weight and composition (dual-X-ray absorptiometry) were measured, thus enabling the assessment of metabolic adaptation. In this study, participants having provided their consent to be re-contacted will be invited to attend the research center 12,18 and 24 months after completing the lifestyle intervention. Body weight and composition will be measured, aiming to explore the association between metabolic adaptation and changes in body weight and composition after a weight loss intervention. In addition, we will explore whether weight and fat mass changes are different between groups, and whether these effects are mediated by metabolic adaptation.