Body Mass Index (BMI) « Health Now, Wealth Forever

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By Gary, on May 16th, 2010

What is it?  Why do we need it?

It is:  a statistic which measures your body fat based upon your height and your weight only.  The equation is Weight divided by Height.

This Factor is then categorized to determine what is healthy and what is not.  The normal BMI chart displays BMI as a function of Weight (along the horizontal axis) and Height (along the vertical axis).  Using contour lines you can plot your Weight and Height and find your personal BMI.

It does not actually measure you percentage of body fat.  It is only a tool used by physicians and health insurance companies to help them determine your healthiness.  It was developed between 1830 and 1850 by a Belgian Mathematician, Adolphe Quetelet.

The Basic Categories are:

  1. Underweight – BMI < 18.5
  2. Normal – BMI 18.5 to 25
  3. Overweight – BMI 25 to 30
  4. Obese – BMI > 30

A couple of  examples would be:  You are 5′-0″ and weigh 115 pounds.  Your BMI would be 23 (115/5) and you would fall in the “Normal” Range.  Or, if you are 6′-0 and weigh 240 pounds, your BMI would be 40 (240/6) and you would fall into the “Obese” Range.

But what if you are all muscle and have very little body fat?  BMI really does not give you a fair assessment.  You are better served by finding your percentage of body fat by using underwater and skinfold measurements which calculate your Body Volume Index (BVI).

In general, the BMI factors are not looked at as strict measurements of your “fatness” or “thinness”.  They are general at best and must be considered as an aid to determining your health.  Private medical insurance companies use them but modify the levels for overweight and obese.

It is a controversial health index.  Some argue that the error in the BMI is significant and so pervasive that it is not generally useful in evaluation of health. University of Chicago political science professor, Eric Oliver, says “BMI is a convenient but inaccurate measure of weight, forced onto the populace, and should be revised”.

Sources:  World Health Organization web site