BMI in Kids

Because children's weight changes so quickly throughout their growth cycles, the U.S. Center for Disease Control (CDC) measures their fitness using the Body Mass Index, commonly referred to as BMI. Considering a child's BMI will allow a medical professional to determine if he or she is over- or underweight compared to other children of a similar height and age.

Measurement

A child's BMI is determined by comparing his body weight and height. In math terms, body mass equals 703 times the quotient of a child's body weight divided by the square of his or her height. BMI can also be calculated more easily through a BMI chart, located in many doctors' offices. Once the BMI has been calculated, it can be compared against another chart that reports BMIs of other children in the child's height, age and gender category.

Healthy BMI

A healthy BMI is located between the 5th and 95th percentile on the CDC clinical growth charts and varies greatly depending on a child's age. An idea of average BMI can be determined by looking at the 50th percentile. For example, average BMIs for children ages five to eight are between 15 and 16. At age 11, the average goes above 17, and at age 13 it goes above 18. The CDC stresses that all of these numbers only point to the average child for a certain age; having a higher BMI may just mean that a child is big for his age and may not necessarily be an indicator of bad health, nor does an average or low BMI alone indicate good health.

Limitations

Because a child's body composition and health cannot be determined by considering weight alone, the CDC strongly recommends against using BMI growth charts as a sole diagnostic device. By considering a child's general health, body type, whether or not the child has had a recent growth spurt and how active the child is, a doctor can reach a better conclusion as to her level of fitness compared to other children of the same age.

Recommendations

Parents who are concerned about childhood obesity can take a number of measures to ensure that their children have healthy BMIs. According to a study released by Oregon University in January 2010, children are more physically active when their parents attend and support their athletic endeavors. Parents should also watch their own weight; children of obese parents are twice as likely to become obese themselves. Lastly, parents can provide healthy food options for their children at the dinner table. Eating a wide variety of nutritious, low-fat foods will help a child remain a healthy weight.

History

The BMI is a measurement framework that dates back to the early 1800s. It was invented by a Belgian named Adolphe Quetelet, who was creating the study of "social physics," which today would translate into the study of human fitness. It became popular in the 1972 following a paper published by Ancel Keys, who stated that BMI was the best way to easily determine if a person had an appropriate amount of body fat. The National Center for Health Statistics adopted it as a measurement tool for children's health in 1977. Today it is used by physicians to help assess the health of people of all ages.