Approximately 1 in 3 children or adolescents are overweight, the American Heart Association warns, so it's important parents and kids understand what constitutes healthy body weight. The Body Mass Index, a measure of body composition, can determine whether a girl is overweight. Although a girl's BMI is not exactly the same as her body fat percentage, researchers often extrapolate fat percentages using the BMI. Other tools such as calipers can directly calculate a girl's body fat percentage.
Body Mass Index
The BMI is a calculation based upon height and weight. The calculation is the same for everyone, but for kids and teens age 2 to 19, the index takes their age and weight into account. The CDC calls this BMI-for-age. Girls tend to have more body fat than similarly-aged boys, and body fat varies with age. The CDC and other organizations provide online calculators and charts you can use to determine a girl's BMI-for-age.
Healthy Ranges
Generally speaking, a girl's body fat percentage shouldn't be below 15 percent . A British study classified girls aged 7 to 10 as healthy if body fat percentage was between 15 and 25 percent, give or take a point or two. The study classified girls age 11 to 18 as healthy if their fat ranged from about 16 to 30 percent.
Measuring Body Fat
A number of methods exist to test body fat. Calipers, a low-tech approach, have tongs that pinch fat away from muscles. A bioelectrical impedance analysis scale --- a high-tech but low-cost device --- runs an electric current through the body. Many experts consider hydrostatic weighing the best method, but it requires placing a child or adolescent in water. During Dual Energy X-Ray Absorptiometry, two X-rays scan body composition. It's a new and relatively expensive procedure.
Staying Healthy
Overweight girls stand a greater risk becoming unhealthy adults. If a girl's BMI-for-age is above the 95th percentile, skinfold testing may be necessary. Although you may calculate a girl's body fat percentage yourself, only her physician can determine what it means. Girls develop differently than boys, for instance, and a higher body fat level doesn't always mean a girl is unhealthy.
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