Clinical Obesity Beyond BMI Identifies a Large High-Risk Subgroup in United Kingdom 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 compares 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, whereas clinical obesity was further characterized by obesity-related organ dysfunction. Prevalence, disease burden, incident outcomes, and predictive performance were assessed across obesity categories. Data were collected during 2006-2010 and analyzed in 2026.

The prevalence of BMI-defined obesity was 23.92%, whereas the prevalence of obesity increased to 67.58% under the new criteria, with clinical obesity accounting for 62.70% of the total population. Among individuals with a nonobese BMI, 173,698 met the criteria for clinical obesity and exhibited a higher cardiometabolic burden. Compared with individuals classified as nonobese according to both BMI and the new criteria, participants with a nonobese BMI but clinical obesity had increased risks of incident Type 2 diabetes (hazard ratio=3.18, 95% CI=3.04, 3.33), nonalcoholic fatty liver disease (hazard ratio=2.01, 95% CI=1.91, 2.13), chronic renal failure (hazard ratio=1.52, 95% CI=1.46, 1.59), heart failure (hazard ratio=1.37, 95% CI=1.31, 1.44), and thrombosis (hazard ratio=1.36, 95% CI=1.28, 1.45). Disease burden and multimorbidity were higher among individuals with clinical obesity, particularly among those with a nonobese BMI. Although alternative obesity frameworks modestly improved discrimination for selected outcomes, predictive performance remained broadly comparable to BMI-based classification.

Defining obesity on the basis of abnormal adiposity and obesity-related organ dysfunction may increase the estimated population burden of obesity compared with definition by BMI alone. Individuals with nonobese 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.