Debunking BMI

KUFall2012_06This post was prompted by yet another internet news story of a school district gone crazy.  This has become an all-too-common trend as grade-school teachers and administrators have repeatedly begun, in essence, the practice of medicine by making medical recommendations to parents about their children.  In some instances, they go beyond making recommendations  to actually making certain medical treatments a requirement!  More on that another day, perhaps.

This time, it is an elementary school in Belton, Mississippi that has started measuring the Body Mass Index, or BMI, of students and sending reports home to parents. You can read the full article, here:

So, beyond the very borderline ethics of school personnel performing medical procedures, it highlights the fact that the BMI itself is an unscientific measure, with little to no meaningful use.  Despite this, however, the Body Mass Index has been adopted by the government, insurance companies and the conventional medical system as the “be-all and end-all” of health statistics pertaining to obesity.  If you don’t fit a certain BMI profile, you can be denied insurance and other problems.

So, what I am doing here, is evaluating the BMI itself as a measurement.

Definition: what is the BMI?  BMI is a mathematical formula as follows:

BMI= weight (kg) / [ Height (m) ]2

If you are like any inquiring mind, your first thought is probably, why? What is the basis of this formula?

Where did the BMI Come From?  What we now know as the BMI was invented in the 1800s by a Belgian named Lambert Adolphe Jacques Quetelet. Quetelet was a actually mathematician, not a doctor. He produced the formula to give a quick and easy way to measure the degree of obesity of the general population to assist the government in allocating resources. In other words, it is a 200-year-old measure that never had any scientific basis or validity. Some reports suggest that Quetelet gathered the data, then “played with it” mathematically until he found a formula that loosely fit his day.  In other words, he made it up.  It actually does not represent any physiological measure of health.  We’ve actually learned a lot about health and medicine in the last 200 years, and there is no valid reason to keep using the BMI.

– Other measures are actually more accurate.  Waist size and height ratios, for example, are more indicative of the amount of trunkal fat – fat around our internal organs – which in turn is a better indicator of overall health.  The Waist-Hip ratio is a better indicator of heart disease risk, for similar reasons.  Simply looking at waist size is a better indicator of diabetes risk

– Professor Nick Trefethen of  Oxford University has assessed the BMI and feels the formula itself its flawed, as it will tend to make taller people think they are fatter than they really are, while making short people think they are thinner than they really are.

– The main flaw of the BMI seems to be the fact that it treats all mass the same.  Fat is actually less dense than muscle and organs, which in turn are less dense than bones.  Thus, strong, fit individuals who exercise a lot ( athletes, farm workers or other laborers, etc.), will measure higher on the BMI, which medical professionals interpret as unhealthy.  For these people, the BMI is  often grossly inaccurate.

– Another way to think of this is as follows: If you truly are fat, you will have a high BMI.  If you have a high BMI, however, you may not be fat, you could instead merely be muscular and fit.

–  A far BETTER measure is Percent Bodyfat.  Thus, if you weigh 100 pounds, how much of that is fat, compared to how much is non-fat, ie, muscle and organs?  There are a number of ways now of measuring percent body fat.  There are caliper tests, water tank “dunk” tests, and electric  impedance tests.  These measurements are far more accurate with respect to risks for health conditions.  Unfortunately, they are also a  bit more  labor intensive than simply measuring height and getting weight, so some busy clinics chose not to do this test.

In summary, BMI is a 200 year old, badly outdated measurement with NO physiological basis and NO scientific connection to health.  It needs to be immediately abolished.


Leave a Reply

Your email address will not be published. Required fields are marked *