Clinical Obesity Beyond BMI Identifies a Large High-Risk Subgroup in UK Adults

BMI is widely used to define obesity but does not capture adiposity distribution and related functional impairment. This study assessed obesity prevalence, disease burden, and incident cardiometabolic risk using the new criteria proposed by The Lancet Commission and compared disease burden across BMI-based and functional classifications.

A population-based cohort study included 436,751 UK Biobank participants cross-classified according to ethnicity-specific BMI thresholds and the new criteria for preclinical and clinical obesity. Obesity was defined using integrated anthropometric and body-composition measures, while clinical obesity was further characterized by obesity-related organ dysfunction. Prevalence, disease burden, incident outcomes, and predictive performance were assessed across obesity categories. Data collected during 2006-2010 and were analyzed in 2026.

BMI-defined obesity prevalence was 23.92%, whereas obesity prevalence increased to 67.58% under the new criteria, with clinical obesity accounting for 62.70% of the total population. Among individuals with non-obese BMI, 173,698 met criteria for clinical obesity and exhibited higher cardiometabolic burden. Compared with individuals classified as non-obese according to both BMI and the new criteria, participants with non-obese BMI but clinical obesity had increased risks of incident T2D (HR 3.18, 95% CI 3.04 to 3.33), NAFLD (2.01, 1.91 to 2.13), CKF (1.52, 1.46 to 1.59), HF (1.37, 1.31 to 1.44), and thrombosis (1.36, 1.28 to 1.45). Disease burden and multimorbidity were higher among individuals with clinical obesity, particularly among those with non-obese BMI. Although alternative obesity frameworks modestly improved discrimination for selected outcomes, predictive performance remained broadly comparable with BMI-based classification.

Defining obesity based on abnormal adiposity and obesity-related organ dysfunction may increase the estimated population burden of obesity compared with BMI alone. Individuals with non-obese BMI but clinical obesity represent a clinically meaningful high-risk subgroup with markedly elevated cardiometabolic risk. These findings support the clinical utility of multidimensional obesity definitions beyond BMI-based classification.