Your child's Body Mass Index (BMI) is an easy and reliable method of screening for health problems that are correlated with unhealthy weights. It is calculated from your kid's weight, height and age. You can use BMI charts to determine a healthy weight for your child's height. Making sure your child has a healthy BMI is just another important step to help your child be as healthy as possible as he grows older.
How to Calculate a Child's BMI
Calculate your child's BMI by entering his height and weight into one of these formulas:
For metric system calculations, divide his height in centimeters by 100, and then square this number. Then, divide your answer into his weight in kilograms.
weight (kg) / [height (cm/100)]^2
For imperial system calculations, divide his weight in pounds by his height in inches squared. Then multiply your answer by a conversion factor of 703.
weight (lb) / [height (in)]^2 x 703
How to Interpret a Child's BMI
While BMI is calculated in children and adults using the same formula, it is interpreted much differently. For adults, all you need to do is look at a table of BMI ranges to check your weight. For children, who are still growing and may be in various stages of puberty, analysis of BMI is slightly more complicated. The Centers for Disease Control and Prevention (CDC) and the American Academy of Pediatrics (AAP) have developed charts that use age and sex-specific percentiles to interpret BMI. These charts take into account that the amount of body fat is different for boys than girls and that fat changes with age. According to where they fall on the charts, then, children are classified as underweight if they are below the 5th percentile, healthy weight from the 5th to 85th percentile, overweight between the 85th and 95th percentiles and obese if they are in the 95th percentile or higher.
Links to the percentile charts for boys and girls can be found in the Resources section at the bottom of this article.
Health Consequences of Unhealthy Weights in Children
Unhealthy weight in children often becomes an even larger problem later in life, as weight problems exacerbate as your child grows. Therefore, it is important you help your child maintain a healthy weight from a young age, so she can avoid the diseases and conditions associated with being over or underweight later in life. Children and adults who are overweight or obese are at an increased risk of unhealthy conditions such as high blood pressure, diabetes, heart disease, cancer and stroke. Those who are underweight also have an increased likelihood of having heath problems such as a weak immune systems and bones, and malnourishment. Girls who are underweight may not begin to menstruate until they gain a healthy amount of fat.
If your child's BMI is not currently at a healthy percentile, remember that this number can change if your child's lifestyle, diet, or amount of physical activity changes.
Limitations of BMI
BMI is an easy tool for estimating the amount of fat in your body. However, it is not a direct measure of body fatness, since your body weight is comprised of fat as well as muscle. Other tests for weight can be performed on your child to ascertain fat levels with greater accuracy, but it is important to remember that weight is only one factor related to risk for disease. Many other variables may affect your kid's health, so even if you she is at a healthy BMI percentile, she should still see a pediatrician regularly.
Other Methods of Calculating Body Fat
While BMI is an easy way to estimate body fat percentages, it is not the most accurate. If you want to get a better assessment of whether or not your kid has excess fat, there are other tests that can be performed, but you will need to visit your child's pediatrician, who will determine which method is best. Other common tests for measuring fat levels in children include the skinfold thickness test, near-infrared interactance test, and the dual energy X-ray absorptiometry test.
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