PEOPLE who are officially classed as overweight are not necessarily putting their health at risk and going on a diet could be dangerous, according to new research.
A row has been raging after a controversial US study earlier this year found that those deemed to be overweight - because of their high weight to height ratio - actually had a lower chance of dying prematurely than people whose weight was "normal".
Now scientists are increasingly supporting the findings and casting doubt on the value of the body mass index (BMI) system of measuring whether someone is too heavy, according to New Scientist magazine.
This is because it does not take fat levels into account. The BMI method would suggest actor Brad Pitt and George Bush, the US president, are overweight, mostly because they exercise regularly and have built up the amount of lean tissue in their bodies. And experts warned that anyone deciding to lose weight after being told they were too heavy because of their BMI could actually damage their health.
Reducing the amount of food consumed lowers weight, but also lowers the amount of lean tissue, which has been linked to an increased chance of premature death.
Katherine Flegal, an epidemiologist from the US Centres for Disease Control and Prevention (CDC) who led the team behind the controversial study, said: "Although people think there's all this evidence out there showing a high mortality risk associated with being overweight, in fact the literature doesn't show it."
A previous CDC study said overweight and obesity caused 325,000 premature deaths a year in the US, but Ms Flegal's study found that while obesity was the cause of 112,000 early deaths, there were 86,000 fewer deaths a year among those who were overweight compared with those who were "normal" weight.
In Britain, nearly two-thirds of the population are considered to be overweight and about a quarter are obese The NHS Direct website includes a page where people can enter their height and weight and then be given a BMI rating and told whether they are overweight or obese.
But Stanton Glantz, a professor of medicine at California University whose BMI makes him nearly obese, said: "If correct, all these worries about a huge fraction of the population being overweight just go out the window. It's not a trivial problem, but the focus should now be on the severely overweight. The current definition of overweight is not like the speed of light or pi. What was considered as the normal, desirable weight is too low.
"I just got back from a 350-mile bike trip all over the south-west of the US. I lost no weight whatsoever. I was eating like a pig I was so hungry all the time."
Researchers in Denmark and Finland found people who lose weight by eating less food were more likely to die early.
The theory is that dieting results in a decrease in the amount of lean body tissue as well as fat and that this is damaging to health, although the reasons why this appears to happen remains unclear. Losing weight through exercise avoids this problem as it preserves or increases the amount of lean mass.
Dr David Haslam, the chairman of the National Obesity Forum, told The Scotsman that while BMI was useful for population studies, it was "flawed to say the least" when assessing individuals.
"The best way is to get a tape measure and measure your waist halfway between the crest of the hip and the lower rib at the side," he said.
Men with waists of more than 112cm or 40 inches and women with waists of 88cm or 35 inches are considered to be too fat for their health. These figures can be lower for some ethnic minorities, particularly people from south-east Asia.
Dr Haslam said: "If you've got a low waist size but a high BMI you're probably not at increased risk, so it would be foolish to diet. But there are many confounding factors. What people should not take from this is that having extra fat on the abdomen is a good thing. It's not."
How to work it out
TO FIND out your BMI, multiply your height in metres by itself and then divide your weight in kilograms by the resulting figure.
According to the NHS 24/NHS Direct website, if you have a BMI of less than 18.4 you are underweight and between 18.5 and 24.9 you are an ideal weight.
Between 25 and 29.9 you are overweight, between 30 and 39.9 you are obese and over 40 you are very obese.