What Is BMI and Does It Matter?

BMI stands for Body Mass Index.  It is a overly-used, overly-hyped, now largely accepted method of measuring whether one is overweight, underweight, or like Goldilocks and her porridge, ‘just right’.

The problem? BMI is not’ just right’. It can be just wrong, and it is, much of the time, especially for a particular group of people or those with a particular type of body–ironically, athletes and those with low body fat but high muscle percentile–the people we’re all supposed to emulate!

BMI: Designed for National Averages, Not Individuals

Let me explain. Body Mass Index is a simple mathematical formula that is designed to measure or percentage of body fat.  It is an equation that ironically, was never intended to be used on individuals, but in fact was designed in order to find the average body-fat percentage of entire populations.

So when you hear the statistic “60% of Americans are obese or overweight”, you’re looking at BMI being used for the population of the US.  And, for a population average, this is really high. Americans are, generally speaking, a hefty people.

So what’s the problem here? BMI  is now used by physicians everywhere–who could be looking at Arnold Schwartzenegger during his body-building years and would still tell him he needed to lose a few pounds if his BMI said so (actually, Schwartzenegger’s BMI during those years indicated that his was morbidly obese–which tells you how useful BMI is for some people)–as an indication of health or unhealth, when it was never intended to be used on individuals and is, in fact, largely ineffective for indicating whether an individual is a healthy weight or not.

Why Your BMI Might Suprise You

Let me explain how BMI works. The equation cannot, of course, actually measure body-fat, because it is a mathematical equation, not a tool.

All BMI does is calculate what, on average, an inactive person of  average height and typical body composition should weigh–your weight divided by the square of your height. This is fine for people who are of average build and are inactive, but not everyone fits into that category!

Just because BMI calculates one’s weight does not necessarily mean it’s calculating weight that is composed of fat.

Our weight isn’t just fat–it’s a lot of things: bone, fluid, and of course muscle! And the more active, healthy and strong you are, the more muscle you will have! And as we all know–muscle weighs more than fat, mass for mass.

That’s why very active, heavily muscled people and athletes (and even tall, unmuscular people) often have BMI’s that would indicate they are overweight–often heavily overweight, in the case of body-builders or people with exaggerated  muscular composition.

So yes, if you’re extremely sedentary, of average height, have an average build (not narrow and slight nor muscular and strongly built) than having a high BMI can be a definite indication that you need to lose a few pounds.

But if you’re healthy and moderately fit and just happen to be on the muscular, taller, stronger side, you will probably be told you are overweight or obese. And if you’re healthy and moderately fit and just happen to have a narrow, slight build, you will probably be told you are underweight or even anorexic.

Better Ways to Measure

A better way to measure? Look in the mirror. Look around you. Look at the clothing you wear. Do you look fat? Do you look too thin? Do other people think you look fat (or thin)?  Are you healthy, do you exercise and eat right? Are you fatter, thinner, or the same size (not weight) as most other people of the same gender and height? Is it hard to find clothes that fit you because you are fatter or thinner  than most people?

All these things are a much better, much more reliable measurements than BMI. If you really want to know you’re actual body fat percentage, there is a method for doing this using your measurements, which I will try to discuss at some later point.

The BMI Equation

If you really want to know what your BMI is, then here is the equation:

BMI = weight (lb) X 703, divided by height (in) squared

What your BMI indicates:

Below 18: underweight

Between 18 and 24: ideal weight

25 and above: overweight

Above 30: obese