Why BMI Is The Wrong Measurement To Judge Your Success On
When you’re in the middle of a workout regime you need a goal and, for many people, that goal is to reach a target weight that you’re happy with. Most people need a little help with setting that target and that’s where the BMI (Body Mass Index) measure comes in. With a simple calculation it allows you to see if you are underweight, healthy, overweight or obese.
Yet the measure, used by so many people, is fundamentally flawed and you shouldn’t become slave to it. Here’s why…
How is the BMI calculated?
The BMI is calculated by dividing your weight (in kilograms) by your height (in metres squared).
The number delivered from that calculation will then put you into a BMI bracket. For adults this as follows:
*Less than 18.5 is underweight
*The healthy range covers anyone between 18.5 and 24.9
*Between 25 and 29.9 is overweight
*From 30 upwards is the obese range
What’s wrong with BMI?
The main issue with the BMI is that it's a crude measure and makes absolutely no account of the difference between fat and muscle – it all counts the same in your weight. The US website Sporting Charts, for example, shows that the average BMI number for an NFL player is higher than 31
. So basically, on average, an American Football player is obese. The same can be said for many other muscular sports stars such as rugby players in the UK. If you can perform at a top class level of sport, should you really be classed as ‘obese’ – a label that carries its own level of stigma?
In essence the stat works as a broad brush measure to look at trends across the population or large groups of the population. The relationship with height in the measurement means that if you’re probably an average height and not particularly muscular then it’ll work for you. Beyond that it might not help and that’s really not a help if you’re an individual wanting to work towards a specific goal.
What should be used instead?
There have been attempts to right the wrongs of the crude BMI measure. Mathematician Nick Trefethen, Professor of Numerical Analysis at Oxford University, recently came up with a slightly altered version of the formula
, which he says delivers a more accurate result. Yet, despite his best efforts the BMI still feels flawed. Tim Cole, Professor of Medical Statistics at University College London, hit the nail on the head when he stressed that BMI ‘can’t measure fatness because it doesn’t include fatness’.
While there are alternative measurements – see these, for example
– people need to steer clear of obsessing about one broad brush statistic which may have its own flaws and be more specific and varied instead. Aiming for a waist measurement or weight that you are happy with is important and your doctor or gym instructor can help with that. It’s about setting achievable short, medium and long term goals and working out the right diet to fuel the workout plan needed to deliver that (there’s ideas for that at www.fysiqalnutrition.com
It might mean that you have to work a little harder to set the right goals, but avoiding an easy and misleading formula is crucial to judging your success properly.