Atlanta: A big waist increases the risk of heart disease, the American College of Cardiology in Atlanta has been told.

It is not how fat you are but where the fat is, that indicates the risk of having a heart attack, according to the results of an research by Canadian scientists who analysed the waist sizes of 168,000 men and women worldwide.

They found that in men, the risk of heart disease increased by between 21 and 40 per cent for every 51/2in (14cm) extra they put on their waist size. For women, the same increase in heart disease risk occurred for every 53/4in (14.9cm) growth in waistline.

Excess fat around the middle, they say, is more harmful than weight gain on the legs and hips.

This is because fat cells carried-around the stomach are the most dangerous of all, pumping out chemicals that can damage the insulin system. Abnormal levels of these toxins can lead to high blood sugar and unhealthy cholesterol levels, increasing the risk of heat disease and diabetes.

Dr Jean-Pierre Despres, the director of cardiology research at University Laval in Quebec, said: ‘Your risk of having a heart attack has nothing to do with your body mass index.

‘After 20 years of research we’ve learned that it’s not how fat you are that determines your risk to obesity, but where the excess fat is located.’

He added: ‘You could be classed as normal weight but if you have a high proportion of tummy fat you are at increased risk.’

In line with their findings, men and women with a beer gut or apple shape are more likely to be jeopardising their health.

Those carrying the same amount of weight on the thighs and bottom – a pear shape – will be at a lesser risk. Dr Despres added: ‘This is the first time a study of this magnitude has been conducted worldwide in a primary care population.

‘The importance and the clinical significance of these results will stimulate additional studies that will aid us in identifying patients most at risk.’

The Body Mass Index (BMI) is calculated by dividing the person’s weight in kilograms by the square of their height in metres.

A BMI of between 25 and 30 is classed as ‘overweight’, while more than 30 is defined as being obese. The ideal body mass index is between 18.5 and 24.9.

Adult obesity levels in Britain have almost quadrupled in the last 25 years while the rate of child obesity has trebled in the past two decades.

Ten per cent of six-year-olds are obese, rising to 17 per cent in 15-year-olds.