A basic calculation of the ratio between waist and hip size has been identified as the most accurate indicator of the risk of having a heart attack in both men and women. A study of 27,000 people, including more than 14,000 heart disease patients, has found that waist-to-hip ratios can mark out those people more likely to suffer heart failure far more effectively than conventional tests.

While an excessive enjoyment of cigarettes and fast food may be a clear sign of future heart problems, body mass index (BMI) — which is calculated by dividing body weight by the square of your height — has been the most trusted measurement to date.

But researchers have found that measuring the circumference of your waist, and then dividing the number by the circumference of your hips, is far more telling. If the figure — your waist-to-hip ratio — is more than 0.9 for men, or 0.85 for women, then your risks of a heart attack are significantly higher, the study suggests.

Scientists said last night that the report, published in The Lancet, offered conclusive evidence that BMI was obsolete as a means of assessing if overweight people were in danger of cardiac arrest.

The research, the most comprehensive to date and including data from 52 different countries, suggests that the proportion of people at risk of a heart attack is three times higher than previously estimated.

The findings are so siginficant because they show that it is a certain type of fat distribution undetectable by BMI tests that is particularly risky. Researchers found that people with excess abdominal fat were heart attack sufferers, while others could be generally overweight but at no greater risk.

Fat deposited on the stomach — the “beer belly” — is more dangerous than extra pounds on the thighs because the fat cells around the waist pump out chemicals that can damage the insulin system, raising the risk of diabetes and heart disease.

Arya Sharma, co-author and professor of medicine at McMaster University in Canada, told The Times: “A lot of people who do not consider themselves as obese will find they are beyond the cut-off point. Fat on the abdomen is the killer, not fat on the hips.” The British Heart Foundation welcomed the research but suggested more generous waist-to-hip ratio limits of 1.0 for men and 0.9 for women.

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