Waist sizes are getting bigger, and that's bad news for our health - even for those of us who aren't overweight, reports Jane Feinmann

Last month, the World Health Organization launched a campaign - Healthy Weight, Healthy Shape - in a new offensive to fight the pot belly. "A pear-shaped woman may not be an ideal weight. But if she has a small waist as well, she will be at far less risk of developing diabetes or heart disease in later life than someone with the same body weight and more fat round the waist," says Dr David Haslam, a GP and chairman of the National Obesity Forum.

The statistics bear out his concern. Amid an overall increase in obesity - with one in three of us overweight and one in five clinically obese - women are posing particular concern. We have collectively put an inch on our waistlines every decade over the last half century, going from an average of 27in in the 1950s to 34in today. "Women are becoming fatter and they can only put so much weight on round their hips," says Dr Ian Campbell, president of the NOF. "After that, it accumulates on the abdomen, which makes them the same sort of shape as men."

The risks of an apple-shaped body have been known for some years. However, research is beginning to explain why fat in this part of the body is more dangerous. It isn't the subcutaneous fat - the inch (or more) that you pinch - that causes the problems, but the visceral fat, stored deep in the abdomen around several major organs.

"Visceral fat behaves like an independent organ, and when it gets too large it begins to pump out fatty acids, which contain inflammatory and clot-producing compounds, into the bloodstream," explains Judy O'Sullivan, a cardiac nurse with the British Heart Foundation. "Too much of this fat circulating in the bloodstream affects the way the body's insulin works and damages the lining of the artery walls and the heart muscle."

To draw attention to this new health risk, the NOF has just organised a Measure Your Waist Week and Dr Haslam has done the rounds of the party conferences to encourage politicians to push abdominal obesity up the political agenda. The proposed changes centre around current negotiations for a new contract for GPs, to start in April 2006. Organisations like the NOF want GPs to be contracted to take a far greater responsibility for their patients' waistlines.

The standard method for health professionals to track weight has been the Body Mass Index (BMI). Now, research is suggesting that a far more effective system is the simple waist measurement. BMI measurements do not always pick up visceral fat - and that can be dangerous, says Dr Mayur Lakhani, chairman of the Royal College of General Practitioners. "So many Asian men, for instance, suffer heart disease that is not picked up," he says. "And that's often because their BMIs are normal and no one is paying attention to their stomach size."

More GP involvement in weight management will mean more prescribing of anti-obesity drugs. The current top treatment, Xenical, causes fat to bypass the digestive system and can be prescribed on the NHS to anyone with a BMI of more than 30. But with few GPs willing to provide it, a new scheme will allow Boots' pharmacists to prescribe the weight-loss drug on a private basis.

However, another prescription drug option, Rimonobant, due to be licensed in the UK by the end of the year, will be prescribed on the basis of excessive waist circumference rather than BMI. The drug targets abdominal fat, with studies suggesting that, on top of significant weight loss (about 7.4kg in two years), a number of disease risk markers are reduced by 50 per cent more than expected from dieting alone.

So should those who need to prevent, rather than treat, clinical obesity also start measuring their waists?It doesn't really matter, says cardiac nurse O'Sullivan. "The good news is that eating a healthy diet with regular exercise will take fat off the waist more quickly than the rest of the body."

How do you measure up?

Waist circumference is different from belt size. To find it out, follow these simple steps:

* Take off your top and loosen your belt.

* Place a tape measure around the waist at a point 1cm below the navel.

* Measure the waist circumference while breathing out, with the abdomen relaxed.

* A waist circumference of 88cm (35in) for women, and 102cm (40in) for men, indicates that you have a serious risk of developing heart disease or diabetes.

Xenical trials cost £125 for a 12-week programme at Boots; call 0845 070 8090 for participating stores.