For people with heart disease, waist size may better predict risk of early death than overall weight, a new study finds.
Researchers found that normal-weight heart patients who have belly fat have worse survival odds than obese people whose excess pounds are concentrated in their thighs and buttocks.
The findings suggest that heart doctors should consider weight distribution rather than simply body mass index (BMI) -- a measurement based on height and weight -- when assessing a patient's risk, the study authors say.
"Among people with coronary disease, those with the highest mortality are actually those with normal weight who have a central distribution of fat," said lead researcher Dr. Francisco Lopez-Jimenez, a professor of medicine at the Mayo Clinic in Rochester, Minn.
"In people with heart disease, BMI is a terrible way to assess risk," he added.
Fat that accumulates around the belly -- called visceral fat -- is a known risk factor for heart disease. Visceral fat changes how cholesterol is metabolized, increases blood pressure and puts people at risk for diabetes, he explained.
"If someone has extra fat in the belly and a normal BMI, this individual will most likely have a low amount of muscle mass," Lopez-Jimenez added. This suggests that although thin, these people aren't fit.
For the report, released online Jan. 28 in advance of print publication in an upcoming issue of the Journal of the American College of Cardiology, investigators pooled data from five studies that included more than 15,000 patients. Their average age was 66.
This process, called a meta-analysis, relies on findings from several studies to detect a consistent pattern. However, the results of this method are only as good as the strength of the original data.
In this case, during roughly five years of follow-up, almost 4,700 people died. Those of normal weight with belly fat were 27 percent more likely to die than patients considered obese as measured by BMI, but who had less belly fat.
The relationship between BMI and mortality has been much-debated among heart researchers.
This new report comes on the heels of another meta-analysis that revealed a surprising pattern: While obesity increases the risk of dying early, being slightly overweight appears to reduce it.
That study, involving almost 3 million adults, was published Jan. 2 in the Journal of the American Medical Association.
"For people with a medical condition, survival is slightly better for people who are slightly heavier," said study author Katherine Flegal, a senior research scientist at the U.S. Centers for Disease Control and Prevention's National Center for Health Statistics.
Several factors may account for this finding, Flegal added. "Maybe heavier people present to the doctor earlier, or get screened more often," she told HealthDay. "Fat itself may be cardioprotective, or someone who is heavier might be more resilient and better able to stand a shock to their system."
Dr. Gregg Fonarow, a spokesman for the American Heart Association and professor of cardiology at the University of California, Los Angeles, said researchers recognize existence of an "obesity paradox."
"Numerous studies have demonstrated that among patients diagnosed with coronary artery disease . . . patients who are in the overweight and obese categories by body mass index have lower risk of mortality compared to patients in the healthy weight category," he said.
Other studies have shown that central obesity -- measured by larger waist circumference or waist-hip ratio -- is also associated with increased mortality, particularly in those where their BMI is in the healthy weight category, he said.
"The finding of this and other studies suggests that central obesity, which is implicated in the [development] of hypertension, inflammation and insulin resistance, particularly in the setting of low muscle mass, is associated with worse outcomes in coronary artery disease patients," Fonarow said.
Another expert, Dr. David Katz, director of the Yale University Prevention Research Center, argued against using BMI to assess risks for heart patients.
"The simple reality is that BMI is a crude measure of both fatness and fat distribution. It is excess body fat in the wrong places that raises the risk of mortality and morbidity," said Katz.
"This has long been known, and use of the BMI as a proxy measure has mostly been a matter of convenience. This paper suggests the costs of that convenient practice may be high, distorting our assessment of cardiovascular risk."
People who are relatively thin overall but have an excess of fat around the middle are at highest risk, Katz said.
"Many clinicians, myself included, routinely measure waist circumference already," Katz said. "It's simple and readily added to the standard exam. It seems time to add it to the standard of practice as well, since the evidence is increasingly compelling that it is a better measure of what really matters."