Background Metabolically abnormal but normal weight, also called metabolically obese normal weight, is a body phenotype that is not obese on the basis of height and weight, but is associated with increased metabolic risk than is metabolically healthy normal weight. Metabolically healthy obesity, despite increased body weight, is known to be a benign condition in terms of cardiovascular risk.
Objectives The purpose of this study was to analyze the association between knee osteoarthritis and four body phenotypes defined by the presence or absence of metabolic abnormality and obesity.
Methods This was a cross-sectional study using data from 1494 female participants of the Fifth Korean National Health And Nutrition Examination Survey. Radiographic knee osteoarthritis was defined as Kellgren-Lawrence grade of ≥2. Metabolically abnormal state is defined as presence of more than one abnormality among five metabolic factors: waist circumference ≥80 cm, triglyceride ≥ 150 mg/dL, high density lipoprotein cholesterol <50 mg/dL, systolic blood pressure ≥ 130 mmHg or diastolic blood pressure ≥ 85 mmHg, and fasting glucose ≥ 100 mg/dL. Total body fat was measured using dual x-ray absorptiometry and insulin resistance using homeostasis model assessment of insulin resistance (HOMA-IR). Obesity was defined as a BMI ≥ 27.5 kg/m2. Participants were grouped into one of the four body phenotypes based on the presence or absence of metabolic abnormality and obesity: metabolically healthy normal weight (MHNW), metabolically abnormal but normal weight (MANW), metabolically healthy obesity (MHO), metabolically abnormal obesity (MAO). The association between knee osteoarthritis and the four body phenotypes was analyzed using binary logistic regression analysis.
Results The prevalence of each body phenotype was as follows: MHNW 55.1%, MANW 30.3%, MHO 4.2%, MAO 10.4%. Prevalence of knee osteoarthritis was higher in MANW than in MHNW and in MAO than in MHO (MHNW 36.2%, MANW 51.6%, MHO 56.1%, MAO 69.4%). MANW and MAO were characterized by higher age, systolic blood pressure, fasting plasma glucose and insulin resistance compared to MHNW and MHO, respectively. When adjusted for age, the association between knee osteoarthritis and the four body phenotype was as follows: MHNW odds ratio (OR): 1.00 (reference), MANW OR: 1.37 (95% confidence interval [95% CI] 1.07 - 1.76), MHO OR: 2.66 (95% CI 1.55 - 4.58), MAO OR: 3.35 (95% CI 2.27 - 4.95). When normal body weight was defined as a BMI < 25.0 kg/m2, results were consistent.
Conclusions MANW and MAO were more closely associated with knee osteoarthritis than were weight-equivalent, metabolically healthy counterparts, showing the relative roles of biomechanical and metabolic stress in knee osteoarthritis. The results highlight the large proportion of MANW phenotype, which may be at increased risk of knee osteoarthritis, despite non-obese body weight.
Disclosure of Interest None Declared