New Obesity Definition and Clinical Obesity Prevalence for Global Metabolic Bariatric Surgery

Importance: Metabolic bariatric surgery (MBS) is the most effective treatment for severe obesity, yet patient selection and prioritization remain largely based on body mass index (BMI; calculated as weight in kilograms divided by height in meters squared) thresholds rather than clinical conditions. The Lancet Diabetes and Endocrinology Commission recently proposed distinguishing clinical obesity (adiposity with obesity-related organ dysfunction) from preclinical obesity (excess adiposity with preserved function). The implications of this framework for MBS practice have not been evaluated. Objective: To assess the prevalence of clinical and preclinical obesity among MBS candidates and examine their demographic and clinical profiles, perioperative risk, and long-term prognosis. Design, Setting, and Participants: This retrospective, multicenter, cross-sectional study audited data of adults (aged ≥18 years) undergoing primary MBS (laparoscopic gastric bypass or sleeve gastrectomy) between January 1, 2014, and December 31, 2025, at 4 high-volume tertiary centers in the UK, Spain, France, and Brazil. Patients who underwent revisional procedures or multiple bariatric operations within the same year were excluded. Exposures: Classification of obesity as clinical or preclinical using a pragmatic operationalization. Main Outcomes and Measures: The primary outcome was the prevalence of clinical obesity. Secondary outcomes were patterns of organ dysfunction, BMI levels, baseline American Society of Anesthesiologists classification and Charlson Comorbidity Index, estimated 10-year cardiovascular risk (Framingham risk score), and 30-day major postoperative complications (Clavien-Dindo grade ≥3). Comparative analyses between patients with clinical obesity vs those with preclinical obesity were performed only within each individual cohort. No direct statistical comparisons were performed between centers as patient-level data were not shared across cohorts. Results: Among the 2316 patients included, 1709 (73.8%) had clinical obesity (mean [SD] age across cohorts, 45.6 [11.0] to 48.9 [11.7] years; 1149 women [67.2%]) and 607 (26.2%) had preclinical obesity (mean [SD] age across cohorts, 34.7 [10.4] to 40.0 [9.8] years; 486 women [80.1%]). Clinical obesity was the most prevalent category across all centers (from 62.7% in the Brazilian cohort to 79.3% in the UK cohort). Mean (SD) BMI ranged from 40.2 (4.9) (preclinical obesity in the Brazilian cohort) to 48.5 (9.0) (preclinical obesity in the UK cohort), and BMI levels and BMI category distributions (