Don’t Believe The Big Fat Lie About Your Weight

The World Heavyweight Boxing Champ, Anthony Joshua, is fat. Sort of. Actually he’s overweight, bordering on obese. And that’s not us saying it – that’s the result of measuring his Body Mass Index, the formula used by doctors, scientists and governments around the world to measure and assess our weight. Unsurprisingly, the experts are now saying this is a problem, which also explains why just jumping on the scales to see if you are healthy, is like like deciding how many calories are in a meal just by looking at the size of the plate…

1. You’re Not A Formula – You’re Flesh And Blood

The BMI is a well-known formula for calculating your ‘healthy’ weight in relation to your height: your weight in kilograms divided by your height in metres squared. If you score greater than 25, you’re overweight. If your score is 30 or more, you’re obese. Less than 20 and you’re underweight. It is the only practically available tool to most medics.

It sounds very scientific and clever, but actually it was devised as long ago as 1869 by Adolphe Quetelet, a Belgian astronomer who decided that, in adults of ‘normal build’, weight was proportional to the square of the height. He just decided that, all by himself. Sounds like a guess to us…

‘The BMI can’t differentiate between muscle and fat, so Anthony Joshua has a BMI of 28.5’

2. The BMI Can’t Tell The Difference Between Hench And Hefty

The formula has one big flaw: it can’t differentiate between muscle and fat, which explains why Britain’s world heavyweight champion has a BMI of 28.5. NBA star LeBron James – the third-highest paid sportsman in the world after Cristiano Ronaldo and Lionel Messi – has a score of 27.3, while the NFL’s top earner Cam Newton is even closer to being obese than AJ, with a BMI of 29. It’s even worse if you’re a rugby player. England captain Dylan Hartley has a BMI of 32.1, while the slab of muscle that is his team-mate Billy Vunipola scores a Doctor-bothering 35.6.

‘Which weighs more: 10 tons of gold or 10 tons of feathers?’ asks Fitness First personal trainer Simon Cowen. ‘Body fat weighs the same as muscle, but muscle is far more dense than fat,’ he tells RISING. ‘If you’re in training and your BMI is high it may well be a result of power training,’ he adds. ‘That means low reps, high weight and explosive movements, so it takes the same amount of time to lower a weight as it does to lift it. That’s what gives you dense muscles.’

3. It’s Actually All Down To Your Body Composition

It’s not just muscle that the BMI struggles with. It doesn’t account for body type, bone density, stage of growth or genetic factors. ‘You might be fit and active yet still have a high BMI – and there’s nothing more demotivating than working out for months only to be told: “Sorry, according to an equation that dates back nearly 200 years you’re obese,”’ says Cowen. ‘If you do want to lose weight, aim to lose 1-2 pounds a week and view the weight loss as a change of lifestyle – for the long term. An important point to consider is that you will gain some lean muscle when you increase your training and starting eating better. Have a full body assessment done to measure your body fat percentage, and have it tested regularly to measure your progress. Weight loss isn’t rocket science so keep it simple: eat well and burn more calories than you consume.’

‘The BMI doesn’t account for body type, bone density, stage of growth or genetic factors’

4. The BMI Thinks We’re Flat – That’s Flat, Not Fat

‘The formula ignores one fundamental law of physics: that volume, and therefore mass and weight, increases by the cube of the scale factor, rather than the square,’ says Randy Schellenberg, a Canadian scientist who has studied the BMI in depth. According to the BMI, we’re two-dimensional.

That means the BMI doesn’t work for very short people – which Schellenberg says has contributed to a huge rise in the number of pre-pubescent girls diagnosed with anorexia in the US – or very tall people. For example in Gulliver’s Travels by Jonathan Swift, the giant Brobdingnagians are ten times the size of Gulliver, but with the same proportions. This gives them a BMI of 244.4.

‘Have a bodyfat test then set another date to retest – in the meantime focus on training and most importantly your diet’

5. The BMI Might Tell You You’re OK When You’re Not

It gets worse. ‘It’s possible to be obese yet have a perfectly normal BMI,’ sports nutritionist Mayur Ranchordas tells RISING. If that sounds contradictory, it’s not. ‘It’s pointing out another of the BMI’s flaws. A short man with a beer gut and stick legs might have a lower BMI than Dylan Hartley, but is in far more danger of suffering heart disease. Stomach fat is usually the killer.’

The key message seems to be: don’t stress the weight – get your body fat percentage measured accurately, and periodically, instead. ‘Absolutely ignore the BMI,’ adds Cowen. ‘Once you’ve had a bodyfat test set another date to retest. In that time focus on training – and most importantly your diet.’

WHAT NEXT? You don’t have to obsess about your BMI, but you may still want to lose body fat and gain muscle – and you may well be pressed for time. This ten-minute kettlebell workout from Fitness First ticks several boxes: it’s fast, it’s intense and it will help you achieve both of those goals.

Advice is for information only and should not replace medical care or recommendations. Please check with your Doctor before embarking on exercise or nutrition regimes for the first time.