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What is BMI or Body Mass Index ... by Karli Taylor

You hear the term thrown around by doctors and trainers alike, so what is  BMI?  Body Mass Index (BMI) is a formula that uses your weight and height to estimate your body composition and health risks. According to most standards used by health professionals, if your BMI is between 18.5 and 24.9, you're considered in a healthy weight range for your height. If your BMI is between 25 and 29.9, you're considered overweight. The question is- how accurate is that?

The problem with BMI is that it cannot truly estimate body composition by using strictly height and weight. If you were looking at BMI alone as an indicator of health, a muscular individual and a heavy sedentary individual may appear to have the same health risks! For this reason, BMI can be used as a general tool only with people who are either sedentary or recreational in their fitness.

So what can the rest of us use to determine our health risks? The best indicator for everyone is percentage of body fat. Though many websites and books will tell you that BMI is an estimate of body fat percentage, it is simply not possible to estimate using those variables. There are a few different methods to determine body fat, some more accurate than others.

The most accurate measure is hydrostatic (underwater) weighing. This is not a practical method and can typically only be done in a hospital setting. If you have access to this method- go for it!

The next best thing is to get your body fat tested with calipers by a personal trainer. The trainer will pinch 3-10 areas on your body to determine the percentage of your body is made up of fat. Caliper measures may be affected by hydration levels, fullness of muscles bodies and skin thickness. This method also may suffer from more human error than others as the exact location of the pinch may vary. To keep some kind of consistency in this measure, make sure the same trainer administers the test every time you have it done.

Another method often administered by a personal trainer is bio-electrical impedance analysis, or BIA.  This is typically done using a hand held device that sends an electrical wave through one hand into the other.  It takes into consideration your age, weight, height and gender when computing body fat percentage making it a much better measure than BMI.  BIA eliminates the human error associated with caliper testing, but can be skewed by hydration levels, improper use, recent alcohol consumption and bloating.

For an at home BIA fix, there are a number of scales out there today that will send an impulse through your body entering through one foot and leaving through the other. Though this method is not entirely accurate, it will be efficient enough to give you a benchmark for improvement. These measures can be around 10% off of the mark, but will show increase or decrease over time allowing you to measure progress.

So if you are really interested in body composition, stop wasting time on those online BMI calculators and make an appointment with a trainer to get your body fat tested.