Body Mass Index (BMI) is a number calculated from a person’s weight and height. BMI provides a reliable indicator of body fatness for most people and is used to screen for weight categories that may lead to health problems.

What is a BMI percentile?

After 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).

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 screenings.

Is BMI interpreted the same way for children and teens as it is for adults?

Although the BMI number is calculated the same way 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.For adults, on the other hand, BMI is interpreted through categories that do not take into account sex or age.

What are the health consequences of overweight for children and teens?

Children and teens who are overweight may begin to experience health consequences during their youth as well as putting themselves at risk for weight-related health problems later in life.

Overweight children and teens have been found to have risk factors for cardiovascular disease, including high cholesterol, elevated insulin levels, and elevated blood pressure during childhood. One study showed that approximately 60% of overweight children had a least one cardiovascular risk factor, such as high cholesterol or high blood pressure; in comparison, only 10% of children with healthy weight had at least one risk factor. Additionally, 25% of overweight children had two or more risk factors.2

Other health consequences include the following potential prob

    * Type 2 diabetes
    * Sleep apnea (not breathing for at least 10 seconds during sleep)
    * Social consequences including poor self-esteem and social discrimination

In addition to the health problems they may experience during their youth, overweight children and teens are at increased risk for various chronic diseases as adults (including hypertension, type 2 diabetes, and coronary heart disease). Overweight adolescents are at greater risk of becoming overweight or obese as adults,4 about one third of all severely obese adults were overweight children.5

Maintaining a healthy weight during childhood and adolescence may reduce the risk of becoming overweight or obese as an adult. Encourage children and teens to keep up healthy eating habits, participate in physical activity on most (preferably all) days of the week, and limit television viewing.