Body Mass Index Formula

Although the BMI number is calculated using the same body mass index formula for children and adults, the criteria used to interpret the meaning of the BMI number for children and teens are different from those used for adults. For children and teens, BMI age- and sex-specific percentiles are used for two reasons:

The amount of body fat changes with age.

The amount of body fat differs between girls and boys.

The CDC BMI-for-age growth charts take into account these differences and allow translation of a BMI number into a percentile for a child’s sex and age.

Results of the body mass index formula for adults are interpreted through categories that do not take into account sex or age.

Healthy weight ranges cannot be provided for children and teens for the following reasons:

Healthy weight ranges change with each month of age for each sex.

Healthy weight ranges change as height increases.

CDC and the American Academy of Pediatrics (AAP) recommend the use of the Body Mass Index Formula to screen for overweight and obesity in children and teens aged 2 through 19 years. Although BMI is used to screen for overweight and obesity in children and teens, BMI is not a diagnostic tool.

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

The adult calculator provides only the BMI number and not the BMI age- and sex-specific percentile that is used to interpret BMI and determine the weight category for children and teens. It is not appropriate to use the BMI categories for adults to interpret BMI numbers for children and teens.

The interpretation of BMI-for-age varies by age and sex so if two children are not exactly the same age and of the same sex, the BMI numbers have different meanings. Using the Body Mass Index Formula and calculating BMI-for-age for children of different ages and sexes may yield the same numeric result, but that number will fall at a different percentile for each child for one or both of the following reasons:

The normal BMI-related changes that take place as children age and as growth occurs.

The normal BMI-related differences between sexes.

Source: Centers for Disease Control and Prevention

1 Comment »

1. Body Mass Index Formula | Prevent and Decrease Obesity…

   Although the BMI number is calculated using the same body mass index formula for children and adults, the criteria used to interpret the meaning of the BMI number for children and teens are different from those used for adults. For children and teens, …

   Trackback by Lins — 03/08/2009 @ 9:47 am

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