'BMI' a Bust for Predicting Heart Risk
Body Mass Index May Not Be Useful in Predicting Risk From Heart Disease
How to Calculate BMI continued...
Since muscle weighs more than fat, it is possible that many of the people in the study who were considered overweight, with BMIs between 25 and 29.9, were really fitter with more muscle than the patients with lower BMIs. If this was the case, it would stand to reason that they would have fewer heart problems.
"I think the inability of the BMI measure to distinguish muscle weight from fat weight is an important reason for this finding," Lopez-Jimenez tells WebMD.
"Rather than proving that obesity is harmless, our data suggest that alternative methods might be needed to better characterize individuals who truly have excess body fat, compared to those in whom BMI is raised because of preserved muscle mass."
Fat vs. Fit
There is intriguing evidence that two alternative tests -- measuring waist circumference or waist-to-hip ratio -- may be better ways to distinguish between the fit and the fat.
Although BMI has been used in most studies, Lopez-Jimenez says the few studies that have calculated obesity using waist circumference or waist-to-hip ratio suggest that these measures are more predictive of poor health outcomes.
American Heart Association former president Robert Eckel, MD, tells WebMD that he considers waist circumference measurement a routine part of a patient exam.
"I still calculate BMI," he says. "But waist circumference may be a better indicator of cardiovascular disease risk that goes beyond BMI."
A study published late last year found waist-to-hip ratio to be a much better predictor of heart attack risk than BMI in many different ethnic groups.
Researcher Salim Yusuf, MD, and colleagues from the Population Health Research Institute at Ontario’s McMaster University concluded that BMI is a weak predictor of heart attack risk.
But Eckel says measuring BMI may be more beneficial than the studies suggest if patients who are considered overweight or obese end up being treated more aggressively with heart-protecting therapies.
"Someone with a BMI of 30 or above is likely to have other risk factors," he says. "It may be that the better outcomes among heavier people in this study could be explained by more aggressive treatment to control hypertension, LDL cholesterol, triglycerides [blood fats] and glucose [blood sugar]."