Redefining Surgical Outcomes after Metabolic and Bariatric Surgery: An American Society for Metabolic and Bariatric Surgery Narrative Literature Review of Composite Response Metrics and Body Composition

Background Traditional assessment of response to metabolic and bariatric surgery (MBS) has relied predominantly on weight- and BMI-based outcomes. However, these measures, which are important to patients, fail to capture important dimensions of treatment response, including changes in body composition, obesity-related diseases, and health-related quality of life (HRQoL). Objectives To evaluate emerging approaches that incorporate composite response metrics and body composition assessment as outcome measures after MBS, complementing weight and BMI changes, which may not fully capture clinically meaningful improvements. Methods A narrative review of the current literature was conducted to examine composite outcome measures after MBS and body composition changes. Results BMI and conventional weight-based outcomes have limitations in assessing response to MBS and may systematically misclassify outcomes across patient populations. Composite measures such as the Bariatric Analysis and Reporting Outcome System (BAROS), Bariatric Quality of Life Index (BQL), and Swiss-Finnish Bariatric Metabolic Outcome Score (SF-BARI) integrate multiple dimensions of response, including weight loss, improvements in obesity-related disease, complications, and HRQoL. Furthermore, body composition assessment provides clinically meaningful information regarding changes in fat mass, visceral adiposity, lean tissue, and bone mineral density that are not captured by BMI or body weight alone. Conclusions Response to MBS should not be defined solely by weight or BMI change from baseline. A multidimensional framework incorporating composite outcome measures, patient-reported outcomes, and body composition provides a more comprehensive and patient-centered evaluation of MBS outcomes. Future research should focus on standardizing these measures and evaluating their feasibility for integration into routine clinical practice and outcomes reporting.