Undiagnosed Diabetes in Metabolically Unhealthy Normal Weight Adults: A Cross-Sectional Analysis of National Health and Nutrition Examination Survey Cycle 2017-2020 in the United States.

Background/Objectives: Although body mass index (BMI) is a conventional screening tool for type 2 diabetes mellitus (T2D), its reliability as a sole indicator of metabolic health is controversial, and the metabolic profile of a subset of individuals with normal BMI is indicative of obesity-related complications. This study aimed to estimate the prevalence and predictors of undiagnosed diabetes among Metabolically Unhealthy Normal Weight (MUNW) adults. Methods: Data from the National Health and Nutrition Examination Survey (NHANES) 2017-March 2020 were analyzed. Normal weight adults (BMI 18.5-24.9 kg/m2) were categorized into Metabolically Healthy (MHNW) and Unhealthy (MUNW) phenotypes based on the presence of ≥2 metabolic risk factors, including elevated blood pressure, triglycerides, waist circumference, or low HDL cholesterol. The primary outcome was undiagnosed diabetes, defined as HbA1c ≥ 6.5% or Fasting Plasma Glucose ≥ 126 mg/dL. Results: The study population represented approximately 60 million US adults. The prevalence of undiagnosed diabetes was nearly four times higher in the MUNW group (4.84%) compared to the MHNW group (1.28%). In multivariable logistic regression analysis, age and race emerged as significant predictors. Notably, Asian adults exhibited a significantly higher risk of undiagnosed diabetes (OR 6.10; 95% CI: 1.32-28.2) compared to White adults, independent of metabolic phenotype. Conclusions: Reliance solely on BMI may overlook undiagnosed diabetes in normal-weight adults, particularly those with metabolic clustering or of Asian descent. These findings underscore the importance of multidimensional risk assessment integration into preventive care, optimizing clinical management.