BMI. Body Mass Index. It is beyond me why anyone still uses this as a measure of body composition.
First off, let me explain what the BMI is. The BMI is a quick and dirty (and often inaccurate) measure of body composition based on a person’s height and weight.
You then use a chart like this one to determine if you’re overweight, underweight, or just right:
Here’s why I think the BMI is a bogus way to measure body composition:
1) The BMI does not take into account your musculature. If I were to use BMI on elite bodybuilders, they would likely measure as obese even though their body fat percentage is extremely low. Those guys are heavy, but it’s not because they’re obese! It’s because they’ve got so much muscle.
2) The BMI does not take into account frame size or bone density. Although we sometimes hear someone giggle and say “I’m just big-boned” when they weigh in higher than they wanted to, some people ARE just big-boned! For realz!
3) The BMI cannot tell you how much body fat you have, for the 2 reasons above. Many years ago I had someone in a health club measure my body fat with proper instruments (the BMI scale said I was on the low end of healthy – so nearly underweight). They were stunned that my body fat percentage was so high. Why? I have little bones, a small frame, and some decent muscle. I can easily hide extra fat. It’s not until you use the proper tools that you can get an accurate measure of your body composition.
With my clients, I use a variety of methods to measure body composition, depending on their situation. I have a Bio-impedance Body Fat Analyzer, which is portable, un-intrusive, and fairly accurate (my clients who have weight to lose prefer this method). I also have a pair of good, old-fashioned body fat calipers (usually my athlete clients like this method best). I also have a great tool that I got from the Heart and Stroke Foundation that uses your waist circumference to measure your risk factor for heart disease.
For most people, however, the BEST way to know how you are doing with your health, fitness and weight-loss goals is the PANTS TEST. How are your pants fitting? Snug? Time to clean up your diet and exercise a little more. Easy peasy. End of story.