Definition of variables

2001 National Cholesterol Education Program (NCEP) / Adult Treatment Panel III (ATP III) [13] and 2005 American Heart Association (AHA) / National Heart, Lung, and Blood Institute (NHLBI) [14] definition of MetS was used. MetS components are: 1) waist circumference (WC) ≥90 cm in men and ≥80 cm in women (Asian-specific waist circumference cut-offs were based on 2006 International Diabetes Federation definition [15]); 2) serum triglyceride (TG) level ≥150 mg/dL or drug treatment for elevated TG; 3) serum high-density lipoprotein (HDL) cholesterol level <40 mg/dL in men and <50 mg/dL in women, or drug treatment for low HDL cholesterol; 4) blood pressure (BP) ≥130/85 mm Hg, or drug treatment for elevated BP; 5) fasting plasma glucose level ≥100 mg/dL, or drug treatment for elevated blood glucose. The World Health Organization proposed body mass index (BMI) cut-off points of 25 kg/m² for obesity in adult Asians [16]. So we defined non-obese weight and obesity as a BMI <25 and ≥25 kg/m², respectively. MONW was defined as meeting the MetS criteria with a BMI <25 kg/m²; MHO was defined as not meeting the MetS criteria with a BMI ≥25 kg/m². The same method was used to define metabolically healthy non-obese weight (MHNW) and metabolically obese obesity (MOO). 2006 International Diabetes Federation (IDF) definition of MetS called MetS-IDF was also used. MONW-IDF, MHO-IDF, MHNW-IDF, and MOO-IDF were defined same manner by using MetS-IDF criteria.

For a sex-based analysis of general subject characteristics, data on the following variables were collected: age, BMI, WC, average monthly household income, education level (≤elementary school, middle or high school, and ≥college), daily total energy intake, daily proportionate energy intake from carbohydrate, protein, and fat, smoking status (never, past, and current), and daily alcohol consumption (one standard drink = 14 g of pure alcohol, adopted from the National Institute on Alcohol Abuse and Alcoholism). The nutritional survey of KNHANES was conducted by trained dietitians using the 24-h dietary recall method. Daily total energy and macro-nutrients intake were calculated using a food composition table published by the Rural Development Administration of Korea [17]. The contribution of each macro-nutrient (carbohydrate, protein, and fat) to energy intake was calculated as the ratio of calories from each macro-nutrient to daily total energy intake. Physical activity was defined according to the metabolic equivalent (MET) and physical activity level (low, moderate, and high), based on the International Physical Activity Questionnaire data processing and analysis guidelines [18]. A history of stroke was based on a self-reported questionnaire asking if the participants had ever been diagnosed with stroke. So the stroke variable was defined as a self-reported physician's diagnosis of stroke.