The CDC’s Healthy Weight web resources are great for getting in-depth about Body Mass Index information. Here, we’re just trying to break it down into an easily consumed post that allows you to be informed about what BMI and percentiles are if you aren’t familiar with them.
Let’s begin with definitions:
Body Mass Index (BMI) is a number calculated from a child’s weight and height and is a reliable indicator of body fatness for most children and teens.
Be aware that BMI does not measure body fat directly, but correlates to direct measures of body fat. BMI is more or less an inexpensive and easy-to-perform alternative for direct measures of body fat that can help to screen for weight indicators that may lead to health problems. BMI for children is specific to age and sex so be sure to choose the correct BMI measurement chart for your child.
BMI Percentile is how the measured child or teen fares among other girls or boys of the same age.
A child’s BMI is plotted on a CDC BMI-for-age growth chart (for the appropriate sex) so that their percentile ranking can be identified. The growth charts also show what weight categories are considered underweight, healthy weight, overweight or obese. Percentiles are the most commonly used indicator in assessing size and growth patterns of individual children in the U.S.
Here are the BMI-for-age weight status categories and corresponding percentiles:
- Underweight – Less than the 5th percentile
- Healthy weight – 5th percentile to less than the 85th percentile
- Overweight – 85th to less than the 95th percentile
- Obese – Equal to or greater than the 95th percentile
So why are BMI and BMI percentiles important?
Why should you care how your child ranks in his or her age group if he or she appears to be quite healthy?
Well, comparing your child’s growth progress can help in determining potential weight-related problems that a child might have. And actually, the CDC and the American Academy of Pediatrics (AAP) recommend using “BMI” to screen for overweight and obesity problems in children – and they recommend starting this at 2 years of age.
BMI is a screening tool not a diagnostic tool. For example, you may see that your child has a high BMI for his age and sex. That in itself doesn’t mean there is a problem. Your pediatrician needs help you learn if you should be concerned about taking skinfold thickness measurements, evaluations of diet, physical activity, family history, and other appropriate health screenings.
So why use BMI and not just go by weight?
A child’s weight changes rapidly – every month is a new measurement. And this depends directly on growth factors that are not consistent for every child – like height. Some shoot up like weeds months before classmates do, but this doesn’t mean the child is unhealthy. Classmates will soon follow in reaching their new heights – at their own pace. So it is more helpful to use the height-weight ratio to screen them for fat levels.
The CDC’s website has a handy BMI calculator for children that can help you to determine if you should have concerns about your child’s weight. There is also an adult version so you can check up on your own height-weight ratio! After all, children aren’t the only Americans whose obesity rate is rising!
One great bit of news is that swimming is an excellent way to help your child control weight. It is fantastic exercise and has a host of other intellectual, mental and long-term physical benefits – and it’s fun exercise so you won’t get any complaints about asking them to swim!
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