Measuring Overweight and Obesity

The first challenge in addressing overweight and obesity lies in adopting a common public health measure of these conditions. An expert panel, convened by the National Institutes of Health (NIH) in 1998, has utilized Body Mass Index (BMI) for defining overweight and obesity.¹¹ BMI is a practical measure that requires only two things: accurate measures of an individual’s weight and height (figure 1). BMI is a measure of weight in relation to height. BMI is calculated as weight in pounds divided by the square of the height in inches, multiplied by 703. Alternatively, BMI can be calculated as weight in kilograms divided by the square of the height in meters.

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Studies have shown that BMI is significantly correlated with total body fat content for the majority of individuals.¹¹ BMI has some limitations, in that it can overestimate body fat in persons who are very muscular, and it can underestimate body fat in persons who have lost muscle mass, such as many elderly. Many organizations, including over 50 scientific and medical organizations that have endorsed the NIH Clinical Guidelines, support the use of a BMI of 30 kg/m² or greater to identify obesity in adults and a BMI between 25 kg/m² and 29.9 kg/m² to identify overweight in adults.^12,13 These definitions are based on evidence that suggests health risks are greater at or above a BMI of 25 kg/m² compared to those at a BMI below that level.¹² The risk of death, although modest until a BMI of 30 kg/m² is reached, increases with an increasing Body Mass Index.¹

In children and adolescents, overweight has been defined as a sex- and age-specific BMI at or above the 95th percentile, based on revised Centers for Disease Control and Prevention (CDC) growth charts (figures 2 and 3).¹⁴ Neither a separate definition for obesity nor a definition for overweight based on health outcomes or risk factors is defined for children and adolescents.¹⁵

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Developed by the National Center for Health Statistics in collaboration with the National Center for Chronic Disease Prevention and health Promotion (2000)

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Developed by the National Center for Health Statistics in collaboration with the National Center for Chronic Disease Prevention and health Promotion (2000)