To BMI or Not to BMI ...? That is the Real Question

     Summer is the time of year we can feel most body-conscious, and with all the celebrations of the festive season upon us, the media's focus on weight loss and controlling your eating is practically guaranteed!

So it's timely to think about how true the media's messages about weight and body fat really are, and to consider some new information to help you make up your own mind.

If you've got any interest at all in the "Obesity Epidemic", you'll also know that it's based on everyone's BMI (Body Mass Indicator) number. Your BMI is calculated from your height and weight, and apparently says something about the state of your health.

The BMI first came to public attention in the early 1980s when it replaced the height-weight chart we all measured ourselves against, supposedly as a more reliable indicator of health.

Why did the health-weight charts become unreliable? To understand that, we need a quick history lesson: the chart first popped up in 1897, when US life insurance company Metropolitan Life was looking for a way to easily assess the risks of potential policy holders.

A team of statisticians led by Met Life's chief statistician Louis Dublin, collected the only reliable data that was available at the time: weight and height. They analysed the data, developed the charts and released them in 1897.

They then spent the next 50 years persuading the medical profession and the public that their charts had some meaning for people's health. What the chart was really measuring was how old middle-class white males were likely to be when they died, based on their average height and weight. It was a statistical chart that did not account for the quality of their food, fitness, whether or not they smoked, used safe sex practices, or had any risky hobbies or other lifestyle factors. It was only about height and weight.

And it was not developed on data collected from women; instead the data was massaged to have some kind of application for women.

The first charts also allowed for a gradual increase in that average weight over a lifetime. The definition of "overweight" became anything over that average weight - it meant "over average weight". The mortality risk, it was generally agreed, only increased when a person's weight was about 20% over the average weight; and then the increase was only slight.

Until 1942 that is, when the tables were revised downwards. The word average was replaced by the word ideal, and the concept of 'frame size' was introduced. Now if your 'frame' was small, medium or large, your weight range was different. Your frame size was determined by the circumferance of your wrist. The age increment also disappeared and everyone was supposed to maintain forever the weight they were at age 26, assuming of course it was "ideal" to begin with.

Weight ranges were also revised, downwards. The impact of that was that overnight, that half of the population who had previously been 'average' were now overweight - without doing a thing. For the first time, 'average' became 'too fat' and the first "Obesity Crisis" was born.

In 1952 there was another downwards revision - the bottom of each weight range now became the top, and millions more people were classified as 'overweight' and therefore 'unhealthy', overnight. Remember, these numbers were based on height and weight and age of death only, and that was death from any reason.

In the early 1980s Metropolitan Life again revised their tables. Finally research into weight gain and weight loss was producing some meaningful health indicators, and that data showed body fat was not the mortality risk that had previously been believed. So the tables' weight ranges were revised again, this time upwards. The company said: "These are not the weights that minimise the incidence of disease".

But it was too late to back down their position of the past 100 years: the idea that weight alone was an indicator of health had finally become fixed in the culture.

The booming diet industry, and some parts of the medical profession, erupted into an absolute furore. Almost immediately the industry was promoting a new, more reliable measure: the BMI. But it is also a statistical tool, not a health indicator.

It is a calculation invented in the mid-1800s by the Belgian mathematician Adolphe Quetelet as a statistical measure of weight scaled according to height. So from invention it was never intended to be an indicator of general health yet it was introduced as one, and is still used this way today.

Like the early height-weight charts, the BMI only considers height and weight. As a stand-alone tool it is not able to consider factors such as bone density, frame size, muscle or fat density, ethnic norms, nor health-affecting factors like smoking, your emotional state, whether you practice safe sex, or the quality of food intake.

On top of that, in 1998 the US Government adopted the World Health Organisation (WHO) BMI Guidelines, reducing by 2.8 points the changeover from 'normal' to 'overweight' and from 'overweight' to 'obese'. The WHO's figures are based on the world average which includes significant numbers of people in Africa and Asia who are severely malnourished if not actually starving.

The impact of this change was that overnight 30 million Americans suddenly became overweight and another 20 million obese, without doing anything. It was a repeat of the changes in 1949 and 1952 to the height/weight charts that drove the earlier waves of weight loss marketing.

This last change helped to turn body fat into a reason for moral panic, a disease needing both surgical and life-long drug treatment, and gave marketers an easy way to talk about fat as a health issue.

This is of course my opinion. So what do you believe?

I'd suggest you begin by reading some well-researched books, such as Paul Campos' The Diet Myth, Glen Gaesser's Big Fat Lies, J Eric Oliver's Fat Politics, and Francie Berg's Women Afraid to Eat. These will help you assess the information you see and hear in the media, and start to sift out what role body fat really plays in your health.

Then you can make powerful choices to nurture your body regardless of its size, and optimise your health.

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