Waist-to-hip ratio, not body mass index (BMI), is the best obesity measure for assessing a person's risk of heart attack, concludes a global study published in this week's issue of the British medical journal The Lancet.

If obesity is redefined using waist-to-hip ratio instead of BMI the proportion of people at risk of heart attack increases by threefold, calculate the authors.

Previous research has shown that obesity increases the risk of heart disease. However, these studies have mainly been done in populations of European and North American origin. The evidence for other populations is therefore sparse.

In the latest study, Dr. Salim Yusuf, director of the Population Health Research Institute at McMaster University and Hamilton Health Sciences, and colleagues aimed to assess whether other markers for obesity, especially waist-to-hip ratio, would be a stronger predictor of heart attack than the conventional measure of BMI in different ethnic populations.

The investigators looked at BMI, waist-to-hip ratio, waist measure, and hip measure in more than 27,000 people from 52 countries.

Half the participants had previously had a heart attack and half were age and sex-matched controls (individuals who had not had a heart attack and were the same age and sex as cases).

The team found that BMI was only slightly higher in heart attack patients than in controls, with no difference in the Middle East and South Asia.

By contrast, heart attack patients had a strikingly higher waist-to-hip ratio than controls, irrespective of other cardiovascular risk factors.

The researchers found that this observation was consistent in men and women, across all ages, and in all regions of the world.

The authors state that compared with BMI, waist-to-hip ratio is three times stronger than BMI in predicting the risk of a heart attack. Larger waist size (which reflects the amount of abdominal fat) was harmful, whereas larger hip size (which may indicate the amount of lower body muscle) was protective.

The waist-to-hip ratio is calculated by dividing the waist measure by the hip measure. The cut off point for cardiovascular risk factors is less than 0.85 for women and 0.90 for men. A higher number denotes more risk.

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

In an accompanying published comment Charlotte Krageland of the University of Oslo, Norway states: "The main message from the new report is that current practice with body mass index as the measure of obesity is obsolete. For the assessment of risk associated with obesity, the waist-to-hip ratio, and not the body mass index, is the preferred simple measure."

Dr. John Kelton, dean of the Michael G. DeGroote School of Medicine and dean and vice-president, Faculty of Health Sciences, McMaster University, said: "The results of this study will change, on an international scope, how we evaluate patients' risks for heart disease. Being able to easily identify the risk will have a beneficial effect on awareness and treatment."