The formula for calculating the BMI of children ages 2–20 is the same as the formula used in calculating adult BMIs, but the results are interpreted differently.
Interpretation of BMI for children takes into consideration that the amount of body fat changes as children grow and that the amount of body fat is different in boys and girls of the same age and weight.
Instead of assigning a child to a specific weight category based on their BMI, a child’s BMI is compared to other children of the same age and sex.
Children are then assigned a percentile based on their BMI. The percentile provides a comparison between their weight and that of other children the same age and gender.
For example, if a girl is in the 75th percentile for her age group, 75 of every 100 children who are her age weigh less than she does and 25 of every 100 weigh more than she does. The weight categories for children are:
-Below the 5th percentile: Underweight
-5th percentile to less than the 85th percentile:
Healthy weight 85th percentile to less than the
-95th percentile: At risk of overweight
-95th percentile and above: Overweight
The BMI was originally designed to observe groups of people. It is still used to spot trends, such as increasing weight in a particular age group over time. It is also a valuable tool for comparing body mass among different ethnic or cultural groups, and can indicate to what degree populations are undernourished or overnourished.
When applied to individuals, the BMI is not a diagnostic tool. Although there is an established link between BMI and the prevalence of certain diseases such as type 2 diabetes, some cancers, and cardiovascular disease, BMI alone is not intended to predict the likelihood of an individual developing these diseases.
The National Heart, Lung, and Blood Institute recommends that the following measures be used to assess the impact of weight on health:
-BMI
-Waist circumference (an alternate measure of body fat)
-Risk factors for disease associated with obesity. These include high blood pressure, high LDL or ‘‘bad’’ cholesterol
-Low HDL or ‘‘good’’ cholesterol
-High blood glucose (sugar)
-High triglycerides
-Family history of cardiovascular disease
-Low physical activity level
-Cigarette smoking
The BMI gives healthcare professionals a consistent way of assessing their patients’ weight and an objective way of discussing it with them. It is also useful in suggesting the degree to which the patient may be at risk for obesity-related diseases.
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BMI calculations for adults
