Obesity Is Unreliable Predictor of Heart Disease

A new study shows that body mass index (BMI), a commonly used measure of obesity, cannot reliably predict the outcome for patients with heart disease.

Researchers from the Mayo Clinic College of Medicine (Rochester, MN, USA) combined data from 40 studies to determine the association between obesity and total mortality and cardiovascular events in patients with coronary artery disease (CAD). The studies involved a total of about 250,000 obese people with CAD, with an average follow-up of four years. Most of the studies used BMI as a measure of obesity. The investigators found that patients with a low BMI had a higher risk of death than those with a normal BMI.

Overweight patients had better survival and fewer heart problems than those with a normal BMI. Obese people who had had bypass surgery had a higher death rate when compared with people with a normal BMI, while severely obese people had a higher risk of a heart-related death, but not death from other causes. The results were published in the August 19, 2006, edition of The Lancet.

The better outcomes for overweight people may be because they have more muscle than normal weight people, stated the authors. The results therefore demonstrate the inability of BMI to discriminate between body fat and lean muscle, they conclude.

"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 with those in whom BMI is raised because of preserved muscle mass,” said lead author Dr. Francisco Lopez- Jimenez, of the division of cardiovascular diseases at the Mayo Clinic.

Body Mass Index is a measure of relative heaviness/obesity, reached by dividing a person's body weight in kilograms by the height in meters squared. The healthy BMI range is between 18.5 and 24.9. A BMI between 25 and 29 is considered overweight, and a BMI over 30 is considered obese. Because it considers both weight and height, it is usually the measure most often used in research for referring to relative sizes.



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