An anthropometric index of weight and height

Body Mass Index (BMI) is an anthropometric index of weight and height that is defined as body weight in kilograms divided by height in meters squared (Keys et al., 1972).

BMI is the commonly accepted index for classifying adiposity in adults and it is recommended for use with children and adolescents.

   A screening tool

Like weight-for-stature, BMI is a screening tool used to identify individuals who are underweight or overweight. BMI is NOT a diagnostic tool (Barlow and Dietz, 1998).

For example, a child who is relatively heavy may have a high BMI for his or her age or high weight-for-stature. To determine whether the child has excess fat, further assessment would be needed and that might include skinfold measurements. To determine a counseling strategy, assessments of diet, health, and physical activity are needed.

For children, BMI is gender specific and age specific (Hammer et al., 1991; Pietrobelli et al., 1998). Because BMI changes substantially as children get older, BMI-for-age is the measure used for children ages 2 to 20 years.

   An indirect measure of body fatness

BMI is not a direct measure of body fatness. However, BMI parallels changes obtained by direct measures of body fat such as underwater weighing and dual energy x-ray absorptiometry (DXA). BMI can be considered a proxy for measures of body fat.