What is BMI?
Body Mass Index (BMI)
is a number calculated from a child’s weight and height. BMI is a
reliable indicator of body fatness for most children and teens. BMI does
not measure body fat directly, but research has shown that BMI
correlates to direct measures of body fat, such as underwater weighing.
BMI can be considered an alternative for direct measures of body fat.
Additionally, BMI is an inexpensive and easy-to-perform method of
screening for weight categories that may lead to health problems.
For children and teens, BMI is age- and sex-specific and is often referred to as BMI-for-age.
What is a BMI percentile?
After a BMI is calculated
for children and teens, the BMI number is plotted on the CDC BMI-for-age
growth charts (for either girls or boys) to obtain a percentile
ranking. Percentiles are the most commonly used indicator to assess the
size and growth patterns of individual children in the United States.
The percentile indicates the relative position of the child’s BMI number
among children of the same sex and age. The growth charts show the
weight status categories used with children and teens (underweight,
healthy weight, at risk of overweight, and overweight).
BMI-for-age weight status categories and the corresponding percentiles are shown in the following table.
|Weight Status Category
||Less than the 5th percentile
||5th percentile to less than the 85th percentile
|At risk of overweight
||85th to less than the 95th percentile
||Equal to or greater than the 95th percentile
How is BMI used with children and teens?
BMI is used as a screening
tool to identify possible weight problems for children. CDC and the
American Academy of Pediatrics (AAP) recommend the use of BMI to screen
for overweight in children beginning at 2 years old.
For children, BMI is used to
screen for overweight, at risk of overweight, or underweight. However,
BMI is not a diagnostic tool. For example, a child may have a high BMI
for age and sex, but to determine if excess fat is a problem, a health
care provider would need to perform further assessments. These
assessments might include skinfold thickness measurements, evaluations
of diet, physical activity, family history, and other appropriate health