The Body Mass Index sucks. Plain and simple.
Often times we can hear from different sources that BMI is important. That you should watch and keep it in a specific range. But this is inherently wrong and it’s use is misunderstood. And because of that essentially misused.
Why is BMI so bad? BMI is wrong because it categorizes people by taking into account just two factors: the weight, and the height. This can mislead people by potentially placing them in the wrong category. Data suggests that the percentage of incorrect categorization can vary from 25 to 50%.
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How BMI actually works
It uses very simplistic formula with only two variables – your weight and your height.
And the number you have after making that calculation is placing your in different categories:
Here lies the problem with it. We are incredibly complex creatures. A simple measurement like this cannot cover the whole scope of our nature.
In order to have a better understanding of it we should take a brief look at what it was designed to do in the first place.
The History of BMI
The initial concept of the Index was devised by Adolphe Quetelet. Which he described in 1832. He had a passion for statistics and probability which he applied to the human physical characteristics. (Adolphe Quetelet (1796-1874)–the average man and indices of obesity.)
The Body Mass Index was actually first known as Quetelet Index. But later in 1972 Ancel Keys made it more publicly known as the BMI. (Journal of Clinical Epidemiology)
With the increase of the obesity the need and interest in such an index was growing.
Keys was no stranger to the downsides of the simplicity of this measurement and he argued that it is not the best but at the very least a good enough of a measurement. Not only that but he stated that it is appropriate for studies concerning the general population and not on individual basis. Which is something we’ll get to in a moment.
Why BMI Sucks
It got popular mainly because it is very easy to be measured and it is inexpensive. You don’t need any specialized equipment. And almost everyone has access to a scale and a tape measure.
The problem with it is due to its inherent simplicity it has major limitations that can lead to false results.
- It doesn’t take int account variation in the body frame and bone structure – Essentially people with smaller frames could be put into a healthy category while they can be overweight. And people with bigger frames can be classified as being overweight while being perfectly fine.
- It doesn’t take into consideration loss of height due to aging.
- It doesn’t differentiate between the type of body fat.
- One of the biggest problems is that it cannot distinguish between fat and muscle. Thus more athletic and active people can easily fall into the overweight categories.
- It is a vague number – It has been found that the index can underestimate the number of obese people. And since it is not directly connected with the fat percentage it is hard to judge where exactly the line should be drown between been being healthy and overweight.
In a study where more than 1300 participant took part was shown the scale at which BMI can be misleading.
The participants were categories by their BMI. After that they body fat percentage was measured.
The results showed that nearly 50% of the women that were categorized with normal weight by the BMI, in reality, were actually considered obese (>30% body fat). And almost a quarter of the men were miscategorized. (>25% body fat). (Measuring adiposity in patients: the utility of body mass index (BMI), percent body fat, and leptin.)
Given that data it can be argued about its usefulnesses even when watching the general population’s trends.
The reason it is the most commonly used method is that it is really easy to calculate. Hence methods like using MRI’s and CT scans are too much of a hassle and too expensive.
A similar method is measuring the waist-to-height ratio. Which given that people are most likely to put on weight in the waist area could provide a more accurate numbers but again fails to cover the spectrum just like the BMI.
Some other methods have been develop like the Body Volume Index which aims to improve on the limitations posed by the BMI. And the Underwater weighing (a.k.a. Hydrostatic weighing) that can be used to find the body composition.
Arguably one of the most useful methods is the skin-fold measurement. Which can give as a more accurate details and remains relatively easy to do. This is a good way to keep track of the body fat percentage in people who train and athletes.
If you are wondering whether or not you should lower your BMI or not. Keep in mind that those numbers should be taken with a heavy grain of salt as they can be very misleading.
The chances are that they can be placing you in the wrong category.