The Big Problem with the BMI Calculator 

We know that there’s no such thing as the perfect silhouette and the picture of health can take many forms. Still, for the longest time, fitness and medical communities have reduced the complexity of being in shape to a double digit number using a Body Mass Index (BMI) calculator. New research, however, has put a spotlight on the many flaws of this one-size-fits-all formula. 

A narrow perspective  

BMI was introduced in the 1830s – a time when digital calculators didn’t even exist – as an overly simple formula to categorise people based on their weight relative to their height. To calculate your BMI, you take your weight and divide it by your height in metres squared. 

Weight in kg/height in m2 = BMI

As an example, if you weighed 60kg and were 1,6 metres tall – which is 2,56 when you square it – your BMI would be 23.4. 

60kg/2.56 = 23.4

For the record, a BMI of 25 or more is considered overweight, while the healthy range is deemed 18.5 to 24.9.  

While BMI is still widely used, it only tells only a fraction of the story. Why? It fails to distinguish the difference between muscle and fat and disregards important factors such as your sex, bone density and body composition. In short, it’s a flawed metric. 

Muscle versus fat – why it matters!  

Mathematicians have been quick to point out that the BMI formula divides weight by too much in short people and too little in taller ones. As a result, taller people end up thinking they’re more overweight than they actually are while the shorter folks are led to believe they’re thinner.  

The other big issue with BMI is that it tars all your tissues with the same brush and doesn’t account for the fact that muscle weighs considerably more than fat. As a result, an Olympic athlete with a lean yet heavy muscular body will be assigned the same BMI as the heavily padded couch potato of the same height and weight. If you’re viewing both of them through the lens of BMI, both would be considered overweight – but only one of them is taking home the medals.

Watch your waistline  

If BMI is bad math, is there another way to get a quick snapshot of your health? Many global health institutions believe that looking at your waist-to-height ratio is a much better way to do it. This comes after decades of research showing that the size of your waist is strongly linked to your risk of developing type 2 diabetes – the world’s most common health consequence of being overweight. In short, not all fat is created equally – abdominal fat will negatively affect the functioning of your heart, liver and kidneys much more negatively than the kind that clings to your bottom or hips. 

In accordance with this better measurement, the rule of thumb is to keep your waist circumference to less than half your height. As an example, if you were 160cm tall, you’d want to keep your waist size under 80cm. 

The bottom line 

Having a quick formula for anything is always convenient but it’s clear that BMI is an outdated one. New research indicates that it’s much better to watch your waistline. Still, it’s important to realise that we’re all individuals and “healthy” looks different on everyone.