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ABSTRACT. Background: The purpose of this study was to compare classifications of subjects as underweight, normal weight, or obese by body mass index (BMI) and the ratio of body weight to ideal weight (W/IW). Methods: We performed & theoretical comparison of the 2 indices. We compared classifications of the degree of obesity in 1839 women and 5914 men who were followed up in the primary care clinics of a United States federal hospital. Information was extracted from computerized records. Subjects were classified as underweight (BMI < 18.5 kg/m^sup 2^, W/IW < 0.9), obese (BMI > or = 30.0 kg/m^sup 2^, W/IW > or = 1.2), or normal weight (BMI, W/IW values between the cutoff values for underweight and obesity). W/IW values were computed assuming small, medium, and large skeletal frame for all. We compared the classifications of subjects as underweight, normal weight, or obese by BMI and W/IW. We used Cohen's [kappa] ratio to evaluate the agreement between these classifications. Results: Theoretically, the cutoff values of BMI and W/IW for underweight and obesity are not in agreement. Patient data revealed substantial differences in the classifications of subjects as underweight, normal weight, or obese. [kappa] ratios ranged between 0.18 (poor agreement) and 0.71 (reasonable, but not high degree of agreement). In general, [kappa] ratios were higher when assuming large or medium skeletal frame versus small frame. Conclusions: There are substantial discrepancies in classifying the subjects of a population as underweight, normal weight, or obese by BMI or W/IW. These discrepancies may cause confusion when 2 or more indices are used simultaneously to classify the degree of obesity. (Journal of Parenteral and Enteral Nutrition 27:340-348, 2003)
The incidence of obesity is increasing.1 Obesity increases the risk of type II diabetes mellitus, hypertension, or cardiovascular disease2 and the risk of death.3 Evaluation of obesity is, therefore, an important public health issue. The degree of obesity in populations is usually assessed by formulas relating body weight to height, the so-called height-weight indices.4 Height-weight indices include the body mass index (BMI) and different formulations of ideal weight.
BMI is calculated from weight and height as kg/m2,5 and has been used to classify the degree of obesity in major guidelines.1,6 The guidelines of the United States National Institutes of Health...