Is BMI the B all and end all?

BMI, as a measure of one’s weight and fitness, has been around in one form or another since the 1830s.

Throughout much of that period it has been regarded as the most accurate indicator available – ‘available’ being the operative word.

It’s also the easiest and most universal way to gauge the health of a broad group of people. All you need are two indisputable numbers – a person’s height and their weight. Stick those into a simple equation and you’ve got their BMI.

No tests, no examinations, no procedures – just measurements.

But in more recent years, a few anomalies and inconsistencies have called BMI into question.

The most common of these is probably the person who works out regularly, has high muscle mass and low fat levels, is actually extremely fit, but is considered overweight or even obese according to the BMI measure. Elite athletes too, often struggle to meet the BMI standard.

Usain Bolt, who is widely considered the greatest sprinter of all time, has a BMI of 24.5, which has him teetering on the edge of the overweight category (between 25 and 29.9).

Tom Brady, arguably the NFL’s best ever quarterback, has a BMI of 27 which technically makes him overweight.

And pretty much all of the New Zealand All Blacks’ front row are in the overweight or obese category – but try telling them that!

It’s worth noting, of course, that elite athletes are some of BMI’s statistical outliers (it’s that word ‘elite’ which makes them so). But they help make an interesting point.

Similarly, BMI also discriminates against certain ethnic groups who, because of their genetic make-up, tend towards the higher end of the scale.

But for the most part, and for most people, on its own it’s a fairly reliable measure.

However, it becomes more reliable and more accurate when combined with other measures – most notably, waist circumference.

Generally speaking, any excess fat on the body isn’t good. But according to recent studies, it’s that fat that gathers around the abdomen that is particularly nasty.

Several of these studies have documented a link between excess abdominal fat and both heart disease and type 2 diabetes. And one European study across 340,000 subjects found that people who had a BMI in the overweight range combined with a large waist measurement faced an almost identical risk of type 2 diabetes as a clinically obese person.

We often talk about people being ‘pear shaped’ or ‘apple shaped’ – the pear shaped person having more fat around the bottom and the apple shaped having more around the middle.

The reality is that those apple shaped people are at much higher risk than someone of the same weight, with the same amount of body fat, simply because of where the fat is on their body.

And this danger could never show up through BMI alone.

So, when we combine BMI with waist circumference, we get a much more informed view of a person’s weight, health and fitness levels.

At HeadUp, our position on BMI is this.

Whilst it may not be 100% precise for 100% of people 100% of the time, and it has a few inconsistencies and caveats, it’s still an excellent indicator. And it remains the best and most accurate single, simple measure we have. After almost 200 years it still stands up.

Having said that, we know that when combined with other measures it becomes even more accurate.

And as is the case with almost all metrics, the more touchpoints you have cross-referencing each other, the better.

Some numbers will tell us some of the story – often most of the story.

But our quest is to make it easy for people to gather, collect and organise as many data points as possible so that the anomalies, the outliers and the uncertainties are discovered and understood.

We want everyone to have the clearest picture possible.

That’s why we’re sticking with BMI as a big part of the picture, but not the entire picture.