5 Reasons to Boycott the BMI

Boycott the BMI? At some point in your life, you have probably come face to face with your body mass index (BMI). Maybe you found it out using an online calculator, or your treatment center used it to track your progress. Or pre-DSM-5 it was used as a way to diagnose you. Or not diagnose you. But what is the scientific background of this formula that is so commonly used in healthcare? I did some research on the subject and decided to share my results with you dear reader.

I hope by seeing it’s inaccuracies you will be more skeptical of the BMI and not let your BMI validate or invalidate you.

Reason 1 to Boycott the BMI: It wasn’t even designed for its current use

Flashback to the mid-19th century. Belgian mathematician, astronomer, and statistician Adolphe Quetelet derived the Quetelet Index. He had no interest in obesity when he came up with the index. A pioneer in the field of ‘social physics’ Quetlet wanted to define the characteristics of the ‘normal man’ using mathematical analysis. He used data from the heights and weights of the French and Scottish armies to show that most cases fell within the range defined as a person’s weight in kilograms divided by the square of the person’s height in meters.

In 1835 he published his work in the book entitled A Treatise of Man and the development of his aptitudes. The index sat unused for nearly 140 years. Until Ancel Keys came along in 1972 and popularized it when he published a paper in the Journal of Chronic Diseases that coined the term body mass index.

Interestingly enough Ancel Keys explicitly said that the BMI is appropriate for population studies. And inappropriate for individual diagnosis.

Reason 2 to Boycott BMI: One’s health should not be defined by a decimal point.

The BMI uses sharp boundaries that hinge on a decimal point to determine if someone is underweight, ideal, overweight, and obese. A focus on only a number takes away from other important indicators of health such as diet, exercise, and lifestyle.

BMI category ranges

Below 18.5 = Underweight
18.5 to 24.9 = Ideal
25.0 to 29.9 = Overweight
30.0 and above = Obese

Reason 3 to Boycott BMI: It is physiologically incorrect

The BMI formula does not take into account the relative proportions of bone, muscle, and fat in the body. Nor does it distinguish between weight due to muscle or weight due to fat. Muscle has a higher density, more mass per unit volume, than fat. This is why many athletes have high BMIs and are classified as overweight or obese.

Reason 4 to Boycott BMI: It’s a one size fits all approach

BMI does not account for differences in race, gender, and age.

Reason 5 to Boycott BMI: Not all fat is created equal

The percentage of body fat or where fat is distributed is not considered in BMI. Belly fat (fat around the abdominal organs) puts people at risk of more life-threatening diseases such as diabetes and heart disease. Peripheral fat (fat beneath the skin elsewhere in the body) is associated with fewer health risks. Even relatively thin people can have a high level of belly fat. This means they might be healthy by BMI standards, but internally they might be at higher risk of developing health problems.

The BMI is not perfect, it comes with its fair share of inaccuracies.

There’s no single number that can represent a healthy weight. So why are we being held accountable to comply to this metric?

The only answer I could find is that it is convenient, and inexpensive, and insurance companies like it. I believe that it’s time to get over the convenience factor and get innovative. With all the technological advances in medicine that have been made this last century it baffles me that we are still using this heuristic statistical measure. I conclude this post with the words of the inventor of the BMI himself.

The more advanced the sciences have become, the more they have tended to enter the domain of mathematics, which is a sort of centre towards which they converge. We can judge of the perfection to which a science has come by the facility, more or less great, with which it may be approached by calculation.
Adolphe Quetele

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(Last Updated: May 20, 2022)