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Inspiring families with fresh thinking on parenting

Yano — Inspiring families with fresh thinking on parenting

Why our kids aren’t as fat as you think

Posted on 5th April, 2013 | filed under Featured, Well Being


A third of British children are either overweight or obese when they leave primary school, according to the NHS – and the figure is rising year on year. But how do they know this? Our children’s schools haven’t been visited by a civil servant with a tape measure and a set of scales, so how do they calculate it, asks Michael Donlevy? 

The NHS uses the Body Mass Index (BMI). It’s a well-known formula for calculating your ‘healthy’ weight in relation to your height, which the government applies to annual health surveys of about 6,500 households. But what is BMI really? And how accurate is it?

The first shock is that the BMI is ancient. It was devised in 1869 by Adolphe Quetelet, a Belgian astronomer who decided that, in adults of ‘normal build’, weight was proportional to the square of their height. That’s how he devised the formula we still use today: your weight in kilograms divided by your height in metres squared. If your score is greater than 25, you are overweight. If your score is 30 or more, you are obese.

One word leaps out of that definition: ‘adults’. Yet the NHS, the government and the World Health Organisation all use BMI to measure childhood obesity. ‘In children, BMI needs to be entered into the appropriate gender BMI charts as their BMI needs to be calculated as a percentile,’ says GP Dr Ian Campbell. ‘The charts were recently revised so they’re up to date.’

Yet the method is flawed: BMI doesn’t account for body type, bone density, stage of growth or genetic factors. It is, quite simply, over-simplistic. It also fails to differentiate between muscle and fat. Brad Pitt, who is 1.83m tall, weighed 92kg while packing on muscle for his role in Troy, which gave him a BMI of 27.8. Did he look overweight to you?

Randy Schellenberg, a Canadian scientist who has studied the vagaries of BMI, says, ‘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.’ In layman’s terms, he’s making the point that, according to the BMI, we are two-dimensional.

There is also a problem with Quetelet’s use of the words ‘normal build’: BMI doesn’t work for very short people. In the US, Schellenberg says, this has been blamed for a huge rise in the number of pre-pubescent girls who have been diagnosed with anorexia.

He points out that BMI is also inaccurate among tall people, citing an exaggerated but interesting example. In Gulliver’s Travels by Jonathan Swift, the giant Brobdingnagians are 10 times the size of Gulliver, but with the same proportions. This gives them a BMI of 244.4.

Neville Rigby, former director of policy for the International Association for the Study of Obesity, agrees that the tide has turned against BMI. ‘One of the biggest problems is abdominal obesity, which BMI doesn’t take into account,’ he says. ‘Stomach fat, leading to a big waistline, is usually the killer.’ Research in the States, involving more than 17,000 obese Americans, found that the worst combination of cardiovascular risk factors – irrespective of weight – was in people with large waists and narrow thighs.

Australian researchers claim the waist:hip ratio is a more accurate indicator of obesity than BMI. During an 11-year study of 9,000 adults, researchers found that men whose waist:hip ratio was 1.0 or more were more likely to suffer from the cardiovascular problems associated with obesity. Professor Tim Welborn, who led the research, says, ‘Somewhat surprisingly, waist:hip came out far better than anything else, including BMI, cholesterol and blood pressure.’ He even called for the WHO to reconsider its reliance on BMI.

This throws up another problem. ‘It’s possible to be obese yet have a perfectly normal BMI,’ says Rigby. It might sound as if all these experts are contradicting each other, but they’re making a consistent point that BMI cannot take into account body composition. A short child with a big tummy and stick legs might have a lower BMI than his tall, well-built friend, but a greater risk of heart disease. Girth is more important than weight.

The waist:hip ratio also has the benefit of being straightforward – all you have to do is divide your waist in centimetres by your hips in centimetres – yet there is another flaw. ‘Waist circumference doesn’t work for children,’ says Campbell.

Rather than support BMI, maybe this shows we are becoming too obsessed with tape measures and scales. ‘I’ve written often about the need to avoid medicalising weight in children,’ says Campbell. ‘Far better for parents to focus on healthy living, diet and exercise, and the feel-good factor that comes from good food and activity.

‘Evidence shows that many parents don’t, in fact, recognise overweight in their own kids, so I encourage parents to compare their child with others. Do they look heavier? Does he fall behind in running games? Is he getting teased at school? Does she have difficulty getting appropriately aged clothes to fit? And the rest of the family need to look at themselves, because what’s good for the kid is also good for the parents and siblings – a healthy diet and exercise.’

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Why our kids aren’t as fat as you think was posted on 5th April, 2013 by Michael Donlevy under Featured, Well Being

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Michael Donlevy

About the author: Michael Donlevy

Writing was in my blood from as early as I can remember; parenting took longer to come to me. I come from a creative family – my grandad was an opera singer, for example, although that particular gene skipped my generation – and I always loved writing and drawing, so a career in the creative industries was all I ever wanted. And I have been lucky. I have worked on men’s and women’s lifestyle magazines, with a particular slant on sport, health and fitness… genuine lifestyle stuff. I had two stints on men’s magazine Maxim, latterly as Editor, but probably the most fun I had in a full-time job was as Deputy Editor of Men’s Fitness for four years, interviewing sports stars and writing contentious features about things like government health policy, dodgy food labelling and fast food companies sponsoring sport (it’s a good thing, so long as you don’t eat the stuff). More recently I have worked in a freelance capacity, particularly for Flipside, a science and tech-based magazine for teenagers. As well as writing a lot about sport, I also indulge my other great passion – entertainment – as Flipside’s Reviews Editor. So what do I know about parenting? Good question, and one that maybe you should ask my ten-year-old son! He is, of course, my big work in progress. It’s important to me that I try to be the best dad I can and teach him the right things, but also that I learn from him too. I love the fact that parenting is a two-way process. Oh, I also manage a website called realbirthcompany.co.uk – which runs antenatal classes for mums and dads-to-be. The fact that my wife is a midwife probably explains why I know more than most men would ever wish to about pregnancy, birth and caring for a newborn. It hasn’t put me off, and I haven’t passed out either. Yet…
  • http://www.occobaby.com/ Angelique Tonge

    I just stumbled on your blog and Love it! With regards to BMI, I wish there was an “Enjoying Life” gauge. That should matter more than lean or not. I once had lunch with a family and their teenage boy refused to eat because he felt “fat”. Makes me so sad. Healthy choices are vital but for the right reasons – to be healthy but also happy.