For years, BMI has been one of the main tools when calculating body fat. For those unfamiliar with the term BMI, it stands for Body Mass Index. BMI is calculated from someone’s height to weight ratio. Gyms and personal trainers use this calculation frequently because its inaccurate results tend to put the majority of people in the overweight or obese range. So, why is this such a useful tool for gyms and personal trainers? It creates a misconception in the prospective client’s head that they are more out of shape than they realized. Most people believe the BMI because it has been around for such a long time. If it is so inaccurate, why hasn’t the calculation been changed yet?

Let’s begin by learning why BMI is not a good indicator of body fat. All humans are made in different shapes and different sizes. BMI doesn’t account for bone density, muscle mass, or actual body fat. It is purely a calculation based off of just height and weight. A bodybuilder at 3% body fat would most likely be calculated as obese because of the large amount of muscle mass that isn’t accounted for. We all know that a bodybuilder stepping on stage is probably in the best condition of their life, so this must be inaccurate. Funny enough, Arnold Shwarzenegger in his prime weighed 240 lbs on stage at a height of 6’2. He is calculated as morbidly obese, yet he was in the Guinness Book of World Records for greatest physique. On the other hand, the elderly population tends to carry more body fat, less muscle mass, and have less bone density than younger individuals. This would make them most likely overweight, but they will still most likely rate better on the BMI scale than a college athlete. Next, BMI falls into the distinct categories of underweight (less than 18.5), ideal weight (18.5 to 24.9), overweight (25 to 29.9), and obese (more than 30). Take a look at the numbers. So, you’re telling me that if I change from an ideal weight BMI of 24.9 to a 25, I can now be classified as overweight? Wow! That 0.1 really makes a big difference!! We also need to realize that BMI was created almost 200 years ago. Very little was known about the human body at this time, so how can it possibly be accurate? So, why is it so frequently used? It is the most inexpensive way of getting a quick answer, even if it is inaccurate.

Lucky for us, we have a few other accurate alternatives. Unfortunately, they may cost a pretty penny. The two most accurate body fat calculations are from hydro-static testing and a machine called the “bod pod.” With hydro-static testing, they dunk you into a water tank. Muscle is dense and sinks, while fat is buoyant and floats. They calculate these numbers to find your body fat percentage. The “bod pod” works off of the same theory as hydro-static testing, but it uses air instead of water. Both of these tests tend to be within 1% of your actual body fat percentage. If you are looking for accuracy, these are the ways to go. Don’t fall victim to the BMI trick. Even if you don’t want to use one of these tests, you can still get an idea if you are in a healthy body fat range by checking the measurements of your waste. The less weight you carry in your waist, the healthier you will tend to be. Yet, another measurement not accounted for with BMI.

-Tom