Normal-Weight Obesity and Hidden Cardiometabolic Risk in Young Adults: Implications Beyond BMI-Based Classification

BMI is widely used for obesity classification, yet it does not adequately reflect adiposity distribution and related metabolic risk. Normal-weight obesity (NWO), defined as excess adiposity despite normal BMI, has emerged as a clinically relevant phenotype associated with increased cardiometabolic risk. However, its prevalence and implications in young populations remain insufficiently characterized.

To evaluate the prevalence of normal-weight obesity and its association with cardiometabolic risk markers in a cohort of young adults undergoing occupational health assessments.

A cross-sectional study was conducted in 12,874 adults aged 22-30 years undergoing routine occupational health assessments. NWO was defined using a strict criterion (normal BMI with a waist-to-height ratio ≥ 0.5) and an expanded definition including additional adiposity markers derived from body fat percentage and visceral fat estimates. Anthropometric, adiposity-related, biochemical, and lifestyle data were collected using standardized protocols. Multivariable logistic regression models adjusted for age and sex were used to assess associations between NWO and cardiometabolic risk markers.

Among individuals with normal BMI (n = 9290), the prevalence of NWO was 1.79% (n = 166) using the strict definition and 2.30% (n = 214) with the expanded definition. Compared with metabolically healthy normal-weight individuals, those with NWO exhibited higher triglycerides, fasting glucose, and atherogenic lipid indices, along with lower HDL cholesterol (all p < 0.05). In multivariable analyses, NWO was independently associated with elevated triglycerides (OR 4.99; 95% CI 2.90-8.58), an unfavorable triglyceride-to-HDL ratio (OR 7.44; 95% CI 5.19-10.65), and impaired fasting glucose (OR 3.87; 95% CI 2.19-6.82). Associations were consistent across sensitivity and sex-stratified analyses.

Normal-weight obesity is present in a measurable proportion of young adults and is associated with an unfavorable cardiometabolic profile despite normal BMI. The triglyceride-to-HDL ratio was consistently associated with normal-weight obesity and showed marked differences across adiposity-defined phenotypes. These findings highlight the limitations of BMI-based classification alone and suggest that additional anthropometric and metabolic markers may help identify individuals with less favorable cardiometabolic characteristics.