The ideal weight for a child is based not only on weight but also on height, age and gender. As with adults, body-mass index, or BMI, is used to determine a child's weight status. But instead of using this value alone, a comparison is made with children of the same age and gender. This is known as BMI for age, which establishes whether the child is underweight, at a healthy weight, overweight or obese.
BMI for Age
BMI for age is somewhat similar to BMI for adults, since a child's weight in pounds and height in inches are used to calculate the value.
BMI-for-Age = [weight / (height x height)] x 703
The value is then placed on a growth chart. A growth chart is used because BMI is both age- and sex-specific for children and teens, according to the Centers for Disease Control and Prevention. Within a growth chart, the percentile, not the numeric value of body-mass index, helps to classify the weight status of the child.
BMI Percentiles
For any given age, a child's BMI places him within a percentile. For a child to be a healthy weight for his height, age and gender, he must fall within the 5th and 84th percentiles. Below 5th percentile is considered underweight; the 85th to 94th percentiles are considered overweight; and above the 94th percentile is classified as obese.
Reasons for Percentile Rankings
The CDC explains that a children's ideal body fat changes with age, as does body-mass index. Also, a girl's ideal body fat is much different from a boy's. For example, at age 8, a boy with a BMI of 20 is considered obese, while an 8-year-old girl is classified as overweight with the same BMI. An 11-year-old boy with a BMI of 20 is classified as overweight, while an 11-year-old girl with the same BMI is classified as healthy weight. By the age of 13, a BMI of 20 places both boys and girls at a healthy weight.
Function
Although the percentiles offer classifications for weight, they're actually screening tools. Additional assessments are necessary to truly discern whether a child is overweight or obese. Skinfold-thickness measurements coupled with a medical history, dietary habits, activity levels and growth pattern are also taken into consideration when determining weight status.
Significance
Obesity places a child at a higher risk of developing high blood pressure, high cholesterol, diabetes, sleep apnea, asthma and liver disease. A weight-loss or weight-management program is typically used to treat such a condition, depending on the age of the child.
Treatment
Children under the age of 7 are often placed on a weight-management program. This program isn't aimed at weight loss. It's actually geared to help the child maintain his current weight until his height increases to the point where his BMI is healthy. After age 7, children are generally put on a weight-loss program, which should be supervised by a medical professional.
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