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Department of Community Health Wright State University School of Medicine Dayton, OH E-mail: shumei.sun{at}wright.edu
Dear Sir:
We appreciate the informative comments by Owen regarding our recently published article (1). The body mass index (BMI; in kg/m2) is very useful in identifying persons at risk of overweight, obesity, and subsequent morbidity and mortality. As a result of this utility and the increased incidence of overweight and obesity among children (2), BMI was included in the Centers for Disease Control and Prevention’s revised growth charts for US children (3). Because of the large collections of stature and weight data in many surveys, BMI is the variable most often selected for analysis. This is especially true because of the limited availability of measured body-composition values in large national surveys. In our study (1), we used data from participants in the Fels Longitudinal Study from as early as the 1950s and were thus limited to measures of stature, weight, and BMI.
The point raised by Owen regarding the association of BMI with total and percentage body fat is important. There is a considerable lack of data relating BMI to body-composition measures in children, adults, and the elderly. We previously reported associations between BMI and total and percentage body fat from more recent underwater weighing data from participants in the Fels Longitudinal Study (4). Additional similar information from other investigators would go a long way in clarifying the use of BMI in quantifying and qualifying the relations between overweight and obesity and measures of total and percentage body fat and the associated health risks. Note that the relation between BMI and percentage body fat in the study (5) referenced by Owen had used estimates of body fatness derived from bioelectrical impedance analysis, which has a high error rate (6).
Our recent study (1) is an update of similar analyses, which were presented earlier (7). The focus of our more recent study (1) was on the relations between BMI values during childhood (derived from the Centers for Disease Control and Prevention’s revised BMI growth charts) and the risk of high BMIs (> 25 and > 30) in adulthood. Our results indicate that BMI values during childhood can predict the risk of overweight and obesity in adulthood. The identification of these risk factors is important so that children at risk of becoming overweight or obese can be treated to prevent these conditions in adulthood. Because this was our focus, we did not consider the association of BMI with body fatness to be relevant within the framework of our study, especially because no body-composition data were included in the analysis. Clearly, more information is needed on the relation between indexes such as BMI and direct measures of body composition at all ages so that associations between these variables can be interpreted clearly.
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