A tape measure is a more important tool in combating heart disease than a set of bathroom scales, research has found.

The first large-scale international study of abdominal obesity - excess fat around the middle - has found the simple measuring tool is a better guide to the risk of heart disease than body mass index (BMI), the composite measure of weight and height.

Doctors have long known that the more weight a person gains the higher their risk of a heart attack. But the study shows waist circumference matters more than weight. The study, conducted in 63 countries, found that, in men, the risk of heart disease increased by between 21 and 40 per cent for every 14cm (5.5in) increase in waist size.

In women, the same increase in heart disease risk occurred for every 14.9cm growth in waist size.

The risks associated with increasing girth held across all populations, despite the widely varying waist sizes among the 168,000 people who took part.

Although people in Far Eastern nations have smaller waists on average than in the West, their risk of heart disease increased at the same rate as they put on extra inches.

The findings from the study were presented at the annual conference of the American College of Cardiology in Atlanta. It involved 6,000 family doctors who measured the waists of all patients who consulted them on two half-days and took a detailed medical history.

"This is the first time a study of this magnitude has been conducted worldwide in a primary care population," said Jean-Pierre Despres, director of cardiology research at University Laval, Quebec, and a member of the study's executive committee. "The importance and the clinical significance of these results will ... aid us in identifying patients most at risk.

Body mass index, which is established as an indicator of a person's vulnerability to heart disease, does not take account of the wide variation in the shape of individuals and populations, the researchers said. American footballers weighing upwards of 300lbs may cross the boundary for obesity as measured by their BMI, but be healthy because they carry most of their weight as muscle rather than fat.

The type of fat and where it accumulates is more important than the amount. Excess weight around the stomach is more harmful than when deposited in other parts of the body, such as the legs and hips.

Fat deposited deep inside the abdomen, which is seen in an expanding waist, secretes toxins into the bloodstream, raises cholesterol and increases the body's resistance to insulin, essential for controlling blood sugar. A rise in insulin resistance means the pancreas has to produce extra insulin, which can damage other organs, such as the kidneys.

The typical British male has an apple shape, his stomach bulging over his trousers. Women tend to the traditional pear shape as they age, with weight accumulating on hips and legs.

Professor Steve Haffner, from the University of Texas, a member of the study executive, said: "The study confirms to us the importance of measuring waist circumference, alongside current measures ... in identifying patients at increased cardiometabolic risk."

An estimated 30,000 people a year die from obesity-related diseases in Britain.