Pros & Cons of BMI

Body mass index, or BMI, is an easily calculated measure of body fat that correlates well with health risks. Its advantages generally outweigh its limitations. The use of BMI is somewhat controversial in certain cases because of limitations in its treatment of body composition. An important factor in the use of BMI is recognition that it must be interpreted differently for children and adults.

Identification

BMI describes your relative weight for height. The formula is your weight in pounds divided by your height in inches squared then multiplied by 703. A BMI of less than 18.5 represents underweight while a BMI of 18.5 to 24.9 represents a healthy weight, a BMI between 25 and 29.9 represents overweight and a BMI of 30 or greater represents obese. The average BMI of adults in the U.S. is 26.5, according to Eleanor Whitney and Sharon Rolfes in "Understanding Nutrition."

Pros

Measuring BMI is an inexpensive method to screen for weight categories related to health problems, according to the Centers for Disease Control and Prevention. BMI is easy to calculate and correlates closely with independent measures of body fatness for adults. The results are repeatable and consistent.

BMI values of 20 to 25 are associated with the least risk of early death. A BMI of 27 or greater indicates an increased risk of developing health problems, according to Kathleen Mahan and Sylvia Escott-Stump in "Krause's Food, Nutrition, & Diet Therapy."

Cons

BMI does not represent body composition. A bodybuilder with dense bones and muscular build may be labeled as overweight according to BMI classifications when he is clearly not too fat. Elderly persons with low bone density may weigh less than others of the same height. Ethnic differences in body composition may not be reflected in BMI. BMI does not consider how much of your weight is fat and where the fat is located on your body.

The distribution of fat on the body is an important factor to disease risk. Central obesity with fat that accumulates around the abdomen or upper body is a higher risk for heart disease, stroke, diabetes, hypertension and some cancers than is fat that accumulates in the lower body.

Significance

A healthy body weight, according to "Understanding Nutrition," is within the suggested range for height with a fat distribution pattern associated with a low risk of illness or premature death and the absence of risk factors associated with obesity and chronic disease. BMI addresses the height versus weight range and health risk but does not reflect fat distribution.

Considerations

Although BMI is calculated the same way for children and adults, the interpretation for children is different. The amount of body fat in children and adolescents normally changes with age and by gender. Adult categories do not apply to children. Instead, compare your child's BMI with the BMI of other children of the same sex and the same age in months and years on growth charts developed by the Centers for Disease Control and Prevention.

BMI is not intended as a sole diagnostic tool. It is used along with other health markers to assess health status and disease risk.