Why Do We Still Use the BMI Scale?

It doesn’t matter how you measure it, as a country, we are getting bigger.

You can argue until you’re blue in the face about the cause, but you can’t deny the facts. And the facts clearly show that we are gaining more weight than we should be.

One of the most popular ways that we use to determine if people are overweight or not is the Body Mass Index, or BMI.

BMI uses a ratio of height to body weight to measure a person’s percentage of fat mass. Based on one’s percentage, he or she is classified as below weight, normal weight, overweight, or obese. The problem with BMI is that it doesn’t differentiate between actual fat mass and lean muscle mass when plugging your weight into the ratio.

So our standard way of measuring how fat we are doesn’t actually measure our fat.

Wait, what?

The (Brief) History of the BMI

The formula for BMI was created in Belgium between 1830 and 1850. The formula divides a person’s weight by the square of his or her height. I’ll spare you the boring intricacies of the math, but the construction of this formula lends itself to some serious shortfalls. Namely, the lack of differentiating between fat mass and lean mass.

BMI became widely used in the United States in the early 1970’s after an article was published that showed that the BMI was the best scale for measuring body across the entire population fat as more people were becoming obese. The study was careful to point out that BMI can a good tool for measuring the obesity trends across a large population, but it is an incredibly unreliable way to determine the lean mass percentage of individuals.

However, in part because of its ease of usage, the BMI is often used to assess the amount of body fat in individuals.

The Problem With Using BMI for Individuals

I don’t know how much was known about the difference of density between fat tissue and muscle tissue in the 1800’s, but we now know that muscle is denser than fat. Based on the density difference, the same volume of fat and muscle will have different weights, which is where the BMI scale fails for individuals.

If you’re a fit individual that does resistance training regularly, your BMI readings are likely to be quite different from your actual body fat percentage. Consider a serious athlete that is 6 feet tall and weighs 200 pounds likely has a true body fat percentage of 5 or less. However, according to the BMI scale, that same incredibly fit person has a body fat percentage of 27.

There are so many examples of fit and active individuals who have true body fat percentages that are less than 10, yet have BMIs that consider them either overweight or obese that you’d think doctors and insurance companies would have stopped consulting BMI charts for individuals a long time ago.

And you’d be wrong.

Another Option is Available

While some doctors, insurance companies, and even personal trainers (gasp!) continue to use the BMI scale to measure body composition of patients and clients, there is a better option.


My Skin Fold Calipers

The best and easiest alternative to the BMI scale is to use a pair of calipers to take skin fold measurements at a few different sites around the body. These measurements are then inputted into a formula that provides your fat mass percentage.

While not as quick as cross checking between your height and weight for the BMI scale, skin fold measurement only takes a minute or two and are very accurate when measured by someone trained in the proper measuring techniques.

Demand Better

The next time you’re at the doctor’s office, ask to have your body fat percentage measured.

Don’t let them use the BMI scale either. Insist on a better, more accurate measurement. If enough of us demand better, we can make the better be the normal.

And that would be better for all of us.

Have You Ever Had Your Body Fat Measured with Calipers? How Did/Does That Measurement Compare to Your BMI Number?



Filed under Lifestlye

4 responses to “Why Do We Still Use the BMI Scale?

  1. hah! Brilliant article. We did a graphic on the limitations of BMI a little while back: http://bit.ly/15ITVJy but I’ve never considered skin folds as an alternative!
    What are your thoughts on the Bioelectrical Impedance Machines? I’ve not been hugely impressed by them.

    • Thanks.

      The impedance machines are very unreliable so I wouldn’t put too much into any results from them. Too many variables can cause very drastically different readings to be considered reliable.

  2. I have never really bothered with BMI. it’s not really conclusive. This is a good read though. Interesting post.

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