A new study found that heart attack patients had 'strikingly higher' waist-to-hip ratios, irrespective of other heart disease risk-factors. This observation was found to be consistent in men and women across all ages, and in all regions of the world.

Until now, doctors have used body mass index (BMI), a person's weight in kilograms divided by height in meters squared, to judge if someone is overweight.

A BMI of 20 to 25 is considered normal, 30 overweight and more than 30 obese.

But a global study of more than 27,000 people found waist girth divided by hip circumference more accurately predicted who would suffer heart attacks.

Apple Shape Riskier Than Pear Shape

According to researchers, the danger point was more than 0.85 for women and more than 0.9 for men. This is because fat stored around the waist is more likely to affect lipids in the blood and clog up arteries than fat stored around the thighs and hips.

In other words, apple-shaped people are more at risk of heart problems than those who are pear-shaped.

Furthermore, if obesity is redefined using WHR instead of BMI, the proportion of "abdominally obese" people at risk of heart attack increases by three-fold, according to the researchers.

Salim Yusuf, from Hamilton General Hospital in Ontario, Canada, who led the study, wrote in The Lancet medical journal: "The global burden of obesity has been substantially underestimated by the reliance of BMI in previous studies."

His team examined BMI and WHR in more than 27,098 people from 52 nations. Half the participants had previously had a heart attack, while the other half had no history of heart attacks, but were the same age and sex.

The researchers found that BMI was only slightly higher in heart attack patients than in the others, with no difference for people from the Middle East and southern Asia.

But heart attack patients had "strikingly higher" waist-to-hip ratios, irrespective of other heart disease risk-factors. This observation was also found to be consistent in men and women across all ages, and in all regions of the world.

A larger waist size was found to be harmful, whereas larger hip size -- possibly indicating lower-body muscle mass -- was protective.

Waist and hip circumference were recorded using a standard tape measure. For the waist measurement, it was stretched around the unclothed abdomen. Hips were measured at the level of the widest diameter around the buttocks.

BMI Doesn't Matter

The researchers wrote: "Use of waist-to-hip ratio as the index of obesity instead of BMI increases the population attributable risk for myocardial infarction (heart attack) three-fold.

"Our findings suggest that substantial reassessment is needed of the importance of obesity for cardiovascular disease in most of the world."

Dr. Arya Sharma, an obesity expert at Hamilton who took part in the research, said BMI was inappropriate because it did not take into account muscle -- which is heavier than fat -- and it did not show where fat was distributed.

However, WHR shows when fat is stored around the abdomen -- leaking into the blood and wrapping around the essential organs.

"All that you need to define someone's risk of heart attacks is to measure their waist and divide it by their hips, and if that is more than 0.85 for a woman and more than 0.9 for a man you are in a higher risk group and it does not matter what your BMI is," Dr. Sharma said.

He added that the findings had implications for the whole world, including the UK where more than 65 percent of men and 55 percent of women are overweight or obese.

"Globally, it amplifies the problem of obesity because, so far, when you look at the burden of obesity, you look at BMI. But now we look at waist-to-hip ratio, and you will find more people regarded as obese who would not have been beforehand," Dr. Sharma said.

Beer Gut Is Dangerous

He was particularly concerned about the prevalence of childhood obesity in the western world -- figures show one in five 12-year-old children in Scotland is clinically obese.

"When you have an epidemic of this magnitude, it requires prevention on a large scale through public health measures," he said.

Dr. Christine Edwards, a senior lecturer in human nutrition at Glasgow University, said the Scottish stereotypical beer gut was more dangerous than having a pear-shaped body. "A huge beer gut is going to be at very high risk whereas somebody who has a more even body shape has much less risk, even if they weigh more, because some of that may be muscle and it is evenly distributed across the body," she said.

Dr. Edwards has long recommended patients measure their waists rather then get hung up over the more complicated BMI calculation -- not least because it is simpler to use a tape measure. Men should have waists measuring less than 37 inches and women less than 32 inches.

Ellen Mason, a cardiac nurse at the British Heart Foundation, suggested how best to use the new calculations.

She said: "To measure your waist-to-hip ratio, measure the smallest part of your waist and the widest part of your hips. Divide the hip measurement into the waist. For men, the ratio should be less than 1.0, for women less than 0.9 (slightly different from the US figures).

"If someone's waist-to-hip ratio exceeds these guidelines and they have other risk factors for heart disease, they should talk to their GP when they next visit."