Body composition is a part of childhood fitness. We can often evaluate it just by appearance. It is sometimes easy to see if a child has a problem with body composition or if they are growing out of proportion. But sometimes there are numbers that can be helpful in monitoring our children’s body composition. The most common numbers we use are Weight, Weight Percentile, Height, Height Percentile and Body Mass Index (BMI). Usually these numbers need to be taken in context. They are of lesser value when viewed alone but can be very powerful when used in reference with each other and over time. For most children these numbers are not a concern, but in some situations (when discussed with a medical professional) they can help give parents guidance.
Weight
Weight is the first number that enters most parents’ minds when they think of body composition. Weight forms the bases of measuring body composition. Understand, the normal weight for each child is not one specific number but consists of a range. The normal weight range for each child is dependent on their height and sometimes body type. It is obvious that a child who is taller can have more body mass and still be fit. A child’s weight over time is also an important marker. But an even more important marker is the child’s weight percentile.
Weight percentile
The child’s weight percentile is a measurement of how a child’s weight compares to other children of the same sex at the same age. This number is going to be between 1%-99%. A child that is 50% is right at average for their age. If the number is lower, then that child is lighter than most children their age and if the number is higher than 50% then they are relatively heavier than the average child that is their age. This number is meaningless without knowing a child’s height percentile. Being in fit body composition depends on these two numbers (weight percentile and height percentile) being relatively proportioned. If the numbers are similar it does not matter if they are both high, low, or near average. The child will most likely be fit if the numbers are similar. They do not have to be exactly the same. Again there is a range in what is normal or fit. Fitness also depends on the child’s body type. I have personally seen children who have a higher weight percentile than their height percentile and because of their body type they were very fit.
With weight percentile, time can also be an important part of the picture. If the percentile trend over time is becoming more proportioned then as parents we know we are making correct adjustments in our children’s activity and caloric intake. If we are noticing a trend where our child’s weight percentile is consistently outpacing their height percentile then adjustments may need to be made. To get the numbers more proportioned we often do not need the child to lose weight. What the child needs is that their weight gain to slow or stop so that the percentile will decrease over time until it is more similar to their height percentile.
BMI (Body mass Index)
The last number to discuss is the BMI or Body Mass Index. Strictly speaking BMI is a person’s weight divided by the square of their height taken times 703. Typically people do not calculate this number. In fact I don’t remember ever actually doing the calculation. Rather we use an online calculator or if you are using an electronic health record like in a physician’s office the computer does the calculation for you. Practically, BMI is a person’s weight relative to their height.
How can a parent use BMI? First off I recommend not calculating your child’s BMI at home. I think it is best suited to only be used in the setting of a healthcare provider. If you are monitoring your child’s BMI at home there is a good chance you are putting too much emotional stress on them. In the Doctor’s office the BMI percentile is sometimes used to determine obesity or severe obesity. My thoughts are this is really not needed to be communicated to a young child or even a teenager. What should be communicated is that there is a miss proportion in weight and height and it can lead to health consequences.
For me the best use of BMI is to monitor a child’s progress. Once it is determined that there is a health concern with weight then as a parent you can make changes in activity and food consumption. The BMI can be used to tell if those changes are working. As a child becomes better proportioned then their BMI will decrease.
This blog has attempted to present the numbers used to monitor body composition. It has been a superficial introduction. There is a very deep psychological aspect to these numbers that needs to be addressed. At this time I will just say be careful how you speak to your child about these numbers and you may not need to speak to them at all. Choose your words wisely and get the help of a healthcare provider. Please monitor this blog as we will have more discussion in the future.
