Put on weight at Christmas? Relax - it may not be bad for your health

GLUTTONS who have eaten too much during the festive period can relax - they may not be as overweight as they think.

Researchers in the United States believe the international measure of obesity - the Body Mass Index (BMI) - is too strict, and labels people as overweight even though they will go on to live as long a life as those considered to be perfectly healthy.

Obesity experts said the latest work reinforced their previous calls for waist size to be used in conjunction with BMI calculations to determine health risks.

According to the unpublished research by Dr Jerome Gronniger, of the US Congressional Budget Office, data from more than 33,000 US adults showed the highest life expectancy was among people with higher scores than their optimum BMI.

BMI is calculated by combination of a person's height and weight. The score is reached by dividing the weight in pounds by the square of the subject's height in inches, then multiplying the result by 690.

Traditionally, a BMI of between 20 and 25 is viewed as optimal. This is equivalent to 11st 3lb for a 5ft 10in man, and 9st 9lb for a 5ft 5in woman.

People with BMIs of more than 25 are classed as overweight, while those whose BMI exceeds 30 are termed obese.

However, Dr Gronniger's research, which was reported yesterday, showed that male life expectancy is greatest among those with BMIs of about 26.

That would be classed as overweight under the old rule, and equivalent to 24lb extra for the typical man.

For women, the study found an optimum BMI of about 23.5, around half a stone heavier than the standard.

The study also found that people with BMIs as high as 35 have virtually the same life expectancy as those whose BMI is as low as 20.

It concluded that only people with a BMI of greater than 35 faced a markedly reduced life expectancy.

Dr Gronniger said: "This work does not support the idea that reducing weight alone would result in any large mortality-risk reduction for most of the population."

The main drawback to using the BMI alone is that it does not take fat levels into account.

BMI scores would suggest that actor Brad Pitt and US President George Bush are overweight, mostly because they exercise regularly and have built up the amount of lean tissue in their bodies. Experts have also 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.

The UK's National Obesity Forum (NOF) said waist size was a much better predictor of health risks.

Dr Colin Waine, its chairman, and a visiting professor at Sunderland University, said: "BMI does not tell us anything about body composition, which is why the NOF has campaigned to have waist size included.

"Two men could have an identical BMI, but one might not have an ounce of visible fat, while the other is grossly obese."

Dr Waine said waist sizes of 40in for men and 37in for women were the danger points, above which health risks increased "extremely rapidly".

However, he said BMI should not be entirely abandoned because it had been the basis of decades of research.