Defining Obesity Under the Lancet Commission Criteria: Metabolic Syndrome–Anchored Body Fat Percentage Thresholds in Korean Adults

AIMS: The revised Lancet Commission framework prioritizes excess adiposity over body mass index (BMI) alone for diagnosing obesity, emphasizing population-specific body fat assessments. However, body fat percentage (BFP) thresholds reflecting adiposity-defined obesity remain limited, particularly by sex and age in Asian populations. This study aims to compare BMI- and adiposity-defined obesity classifications and derive sex- and age-specific BFP thresholds in Korean adults. MATERIALS AND METHODS: Data from 18 254 adults who underwent routine health examinations were analysed, with BFP assessed using multifrequency bioelectrical impedance analysis. Adiposity-defined obesity was classified per Lancet Commission criteria using waist circumference, waist-to-height ratio and BMI. BFP thresholds were derived from logistic regression as the values at which the predicted probability of metabolic syndrome matched its observed prevalence among individuals with adiposity-defined obesity. Confidence intervals (CIs) were estimated using bias-corrected and accelerated bootstrap. RESULTS: Adiposity-defined obesity was more prevalent than BMI-defined obesity, with discordance increasing with age, particularly among women. Overall, 6.6% were classified as obese solely by adiposity-based criteria, rising to 11.1% in men and 15.8% in women aged ≥ 65 years. Overall BFP thresholds were 27.8% (95% CI, 27.4%-28.2%) for men and 39.5% (38.9%-40.2%) for women, with minimal age variation in men but reaching 41.0% (38.8%-43.9%) among women aged ≥ 65 years. CONCLUSIONS: Adiposity-defined obesity identifies phenotypes missed by BMI, particularly in older adults. BFP thresholds derived from adiposity-defined obesity vary substantially by sex and age. These findings support adiposity-centred diagnostic approaches and provide sex- and age-specific BFP thresholds for Korean adults.