Metabolic Syndrome in Normal-Weight Americans New definition of the metabolically obese, normal-weight individual MARIE-PIERRE ST-ONGE, PHD 1 IAN JANSSEN, PHD 2,3 STEVEN B. HEYMSFIELD, MD 1 OBJECTIVE — To determine the prevalence rates and likelihood of the metabolic syndrome and its individual components in normal-weight and slightly overweight individuals (BMI 18.5– 26.9 kg/m 2 ). RESEARCH DESIGN AND METHODS — There were a total of 7,602 adult partici- pants of the Third National Health and Nutrition Examination Survey, a nationally representa- tive cross-sectional survey. Prevalence and odds ratios (ORs) of the metabolic syndrome, defined according to National Cholesterol Education Program Adult Treatment Panel III criteria, were computed according to 2.0- to 2.5-unit increments in BMI. RESULTS — Depending on ethnicity and sex, the prevalence of the metabolic syndrome increased in a graded fashion from 0.9 –3.0% at BMI 18.5–20.9 kg/m 2 to 9.6 –22.5% at BMI 25.0 –26.9 kg/m 2 . Compared with men with BMI 18.5–20.9 kg/m 2 , the odds for the metabolic syndrome were 4.13 (95% CI 1.57–10.87) for men with BMI 21–22.9 kg/m 2 , 5.35 (2.41–11.86) for men with BMI 23–24.9 kg/m 2 , and 9.08 (4.23–19.52) for men with BMI 25–26.9 kg/m 2 after controlling for age, ethnicity, education, income, physical activity, smoking status, and alcohol and total fat, saturated fat, carbohydrate, and fiber intakes. The corresponding ORs in women were 4.34 (2.08 –9.07), 7.77 (3.95–15.26), and 17.34 (9.29 –32.38). CONCLUSIONS — Individuals in the upper normal-weight and slightly overweight BMI range have a relatively high prevalence and are at increased risk of having the metabolic syn- drome. Therefore, screening in individuals with normal or slightly elevated BMI is important in the prevention of diabetes and cardiovascular disease. Diabetes Care 27:2222–2228, 2004 T he concept of the metabolically obese, normal-weight (MONW) in- dividual was originally developed 20 years ago (1,2); however, a formal definition has not been developed. When it was originally introduced, it was sug- gested that MONW individuals were those whose BMI (weight in kilograms di- vided by the square of height in meters) was considered normal but who had any one of the following metabolic disorders that could be improved via caloric restric- tion: type 2 diabetes, hypertension, and hypertriglyceridemia (1). The metabolic syndrome is a constel- lation of diabetes (3), hypertension, and dyslipidemia risk factors that are easily and routinely assessed by physicians. The Third Report of the National Cholesterol Education Program Expert Panel (Adult Treatment Panel III) not only draws atten- tion to the importance of the metabolic syndrome but also provides the first prac- tical definition of this syndrome (4). We propose that individuals whose BMI is within the normal to slightly elevated range, 18.5–26.9 kg/m 2 , but who also ful- fill the criteria for the metabolic syndrome be classified as MONW. A previous study reported that 24% of the U.S. population had the metabolic syndrome (5) but did not report the prev- alence of this syndrome among individu- als within the various BMI categories. Although Park et al. (6) have shown the prevalence of the metabolic syndrome across broad BMI categories, they have not examined each metabolic syndrome component individually and did not demonstrate the risk of having the meta- bolic syndrome across the normal-weight range. The main objective of this trial was to examine the prevalence of the metabolic syndrome and each of its components in the U.S. population, specifically focusing on individuals who had normal BMI and those who were slightly overweight. RESEARCH DESIGN AND METHODS — Between 1988 and 1994, a representative sample of the U.S. population participated in the Third Na- tional Health and Nutrition Examination Survey (NHANES III). NHANES III was conducted by the National Center for Health Statistics to estimate the preva- lence of major diseases, nutritional disor- ders, and risk factors for these diseases (7). The complex sampling plan used a stratified, multistage, probability cluster design. The total sample included 33,199 subjects. Full details of the study are avail- able elsewhere (7). Participants gave in- formed consent, and the protocol was approved by the National Center for Health Statistics. ●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●● From the 1 Institute of Human Nutrition, Obesity Research Center, Columbia University, New York, New York; the 2 School of Physical and Health Education, Queen’s University, Kingston, Ontario, Canada; and the 3 Department of Community Health and Epidemiology, Queen’s University, Kingston, Ontario, Canada. Address correspondence and reprint requests to Marie-Pierre St-Onge, Department of Nutrition Sciences, University of Alabama at Birmingham, 1675 University Blvd., Webb 232, Birmingham, AL 35226. E-mail: britainr@uab.edu. Received for publication 21 January 2004 and accepted in revised form 26 May 2004. Abbreviations: MONW, metabolically obese, normal weight; NHANES III, Third National Health and Nutrition Examination Survey. A table elsewhere in this issue shows conventional and Syste `me International (SI) units and conversion factors for many substances. © 2004 by the American Diabetes Association. Metabolic Syndrome/Insulin Resistance Syndrome/Pre-Diabetes O R I G I N A L A R T I C L E 2222 DIABETES CARE, VOLUME 27, NUMBER 9, SEPTEMBER 2004