Maintaining a healthy body weight is an important first step on the road to sustained health. With childhood obesity on the rise, body mass index, or BMI, is a useful screening tool to identify weight problems in kids and teens, according to the Centers for Disease Control and Prevention. The BMI is a number calculated from a person's weight and height. For kids and teens, that number is then assigned a percentile based on the child's age and sex. A healthy weight falls between the 5th and 85th percentiles.
About BMI
The CDC calls the BMI a reliable indicator of body fatness for kids and teens. It does not measure body fat directly, but the BMI is less expensive and more convenient than more precise methods, such as underwater weighing and dual energy x-ray absorptiometry. Used as a screening tool, the BMI can help detect weight-related health problems in kids, starting at age 2. Regardless of a person's age or sex, the BMI is calculated by multiplying weight in kg and dividing the product by the square of height in meters. For teens, the number derived is then plotted on a graph and assigned a percentile based on age and sex. See the References for a link to the CDC's site for determining BMI percentile for teens.
BMI Percentiles
Four percentile ranges exist, and each is assigned a weight status category. Underweight is less than the 5th percentile, while overweight is from the 85th to less than the 95th percentile. A teenager is considered obese if his weight is at the 95th percentile or above. A healthy weight is anywhere from the 5th percentile to the 85th percentile.
Adults vs. Teens
In adults, a healthy BMI falls between 18.5 and 25. But this range does not apply to kids or teens, notes the CDC, as the amount of body fat changes with age, and it differs between girls and boys. For this reason, the percentile is used, which takes into account a teenager's age and gender. For example, a 10-year-old boy with a BMI of 23 would be classified as obese, but a 15-year-old of the same BMI is in the healthy weight category.
Considerations
Parents often want to know what their child should weigh. Healthy weight ranges are not provided for teens, due to changes in height that occur as a child grows. Because of differences in the onset of puberty between boys and girls, these changes are gender-specific. It is therefore important to determine the percentile that applies to your teen. The CDC recommends that teenagers whose BMI percentile falls above the range considered healthy undergo additional testing to determine body fatness. This may include measurements of skinfold thickness and assessments of diet and physical activity. For further information, talk to your doctor.
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