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Body Mass Index (BMI)


BMI

Frustratingly (for me, GP, at least), the Body Mass Index (BMI) appears to be the most commonly used measure of health and fitness. It should be remembered, the BMI is only a unit of measure of body weight in relation to height, which is only one factor to consider when measuring someones health - it does not necessarily identify a healthy individual. However, this is not the reason for my frustration.

My main frustration is the fact that many (but not all) health, fitness and medical "professionals" do not factor body composition into the equation and provide the client with a FALSE reading. Many of the people I work with are athletes and therefore many of them carry a greater muscle mass, but it would be wrong to categorize a muscular frame as overweight or obese when they clearly are not. In these instances, a body fat percentage test would be a far fairer unit of measure to identify their health status. Again, a body fat percentage test should be performed which does not factor height and weight into its calculations.

In the absence of expensive testing equipment, a 4 site caliper test is a sensible body fat percentage test.

Please find the BMI formula and reference chart below:

Weight (kg) / Height2 (metres) = BMI Score

Example: 85kg divide (1.80m x 1.80m) = BMI Score of 26.2 - Overweight (Grade 1 Obesity)

BMI Chart

Question relating to article:

Q. Please can you explain to me how the BMI unit is derived? In normal thinking It is supposed to be kg/m ? Instead of kg/m2. What is the reason behind the m2?

A. In theory, a different scale/ chart could be created to simply measure weight divided by height, but weight divided by height squared is the common method used since it's inception in the 1800's. Presumably they used height squared to create a scale as a guesstimate of body fat - i.e. BMI score of 25, approx body fat of 25%. It does seem weird that we still use this crude method and scale today so widespread, which was partly my reason for writing the article on that day.

The reason for you to think the equation is weight divide by height is that many will simply use weight and height for analysis, rather than quote a BMI score. Another is that many re-write the equation on forums and blogs, such as weight divide by height and then divide by height again etc.

Best regards,

GP