body mass index (bmi)

Info on BMI measurements and how to use them

BMI stands for Body Mass Index and is a measurement of a person’s height and weight in correlation with each other in order to determine body fat.  It’s important to understand that a BMI measurement isn’t an exact figure, however it is a strong indicator of the body fat percentage.  This makes it a good tool for accessing a person’s health in relation to body fat.

Most people are familiar with the adult BMI calculations, but a special Body Mass Index has now been created for children and teens as well, often times referred to as BMI-for-age.  It’s only sensible that kids age 2-19 have their own scale of measurements because they are continuously growing.  This is going to alter the results, which are dependent upon age and sex of the child in addition to their height and weight. 

Important fact: Obsesity in children has been measured at more than 25% total body fat in boys and 32% total body fat in girls.

Though the math involved can get rather complicated, there are now easy to use BMI Calculators, like this one from the Centers of Disease Control that can help you find out a child’s BMI.  It’s best if you have recent height and weight measurements from a physician, but if not using your own measurements will still work.

Once the BMI is calculated it will give you an actual number which is an estimate of body fat percentage.  This number is then applied to a BMI-for-age chart which will give you the percentile range the child falls in.  Again sex of the child is a factor so there are separate charts for boys and girls.  Based on the BMI percentile the child will belong to one of 4 categories:

Underweight:  below 5th percentile
Healthy weight: 5th up to 85th percentile
At Risk of Being Overweight: 85th up to 95th percentile
Overweight: 95th percentile and over

It’s important to understand that simply using weight isn’t a correct indicator of body fat among children.  Their bodies are growing too rapidly and healthy weight is dependent upon many more factors than that one number.  Additionally, body fat changes with age and there is a significant difference in body fat between girls and boys.  However, as mentioned earlier BMI itself isn’t an exact science but it is a strong indicator which makes it more accurate than using just weight to measure body fat.

If your child’s BMI suggests that they are underweight, overweight or at risk to become overweight consult with your physician to discuss it further.  When your child does have a physical ask your child’s doctor to calculate their BMI as well and get their professional opinion.  Dependent upon what they find further tests can be done to more accurately measure body fat and health related issues.  They can analyze factors like diet and family history and make suggestions for changes based on your child’s needs.

Regardless of your child’s BMI results it’s never too late to begin making healthy lifestyle changes within the entire family.  You are a support system for each other as well as accountability partners in dedicating yourself to living healthy.  There are many resources out there, including our own site, for gaining information as well as tips, tricks and ideas for living healthy day to day for you and your children.