BMI Calculator Low Down

As a personal trainer, clients are always asking me about the BMI calculator. They worry whether their body mass index falls in the “normal” weight category. Sometimes I think they are more worried about this BMI thing than actual body fat percentage

So what is the deal with this thing we call BMI? What does it have to do with weight loss? Well, body mass index is just one way to assess your body composition. Body composition is your body’s total makeup of fat-free mass (muscle, bones, organs etc) and fat mass. More specifically, the BMI calculator helps determine if you are underweight, normal weight, overweight or obese by assessing body weight in comparison to height.

You might see the flaw already. It uses body weight and height without adjusting for fat mass. Yes, it tends to overestimate those that are muscular and those individuals that are athletic, while underestimating those that are small, yet “over-fat” in terms of body fat percentage. However, studies have shown a strong correlation between body mass index and body fat in most people. For that reason, BMI is not a bad place to start when trying to determine a reasonable goal in terms of body weight.

However, I want you to know that it is not totally uncommon for a person to gain muscle and loss fat without a change in the number seen on the scale and, as a result, the BMI number won’t change either. Understandably, this can be frustrating.

For this reason, I repeat, BMI is just a place to start. The best ways to determine your success is by determining your body fat percentage through circumference measurements, skin-fold measurements, and bioelectrical impedance (most gyms offer these services). Last, but not least, and certainly my favorite, the way your clothes fit and how you feel is the best way to determine if you are on the right track.

So, know your BMI, but if your clothes sizes keep dropping don’t stress over the number too much.

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