WEDNESDAY, July 16, 2014 (HealthDay News) -- While a host of cardiovascular ailments are associated with excess pounds, new research supports a puzzling "obesity paradox." It found that overweight heart patients experience fewer heart attacks and higher survival rates after cardiac procedures than their slimmer peers.
Scientists reviewing 36 prior studies found that obese patients were up to 27 percent less likely to die after heart procedures such as coronary bypass surgery or angioplasty than normal-weight patients.
But experts warned that under no circumstances do the results suggest that obesity is good medicine.
"We want to make it very clear that we're not promoting being obese or overweight," said study author Dr. Abhishek Sharma, a cardiology fellow at State University of New York Downstate Medical Center in Brooklyn.
"When we're talking about the underlying reasons for coronary artery disease, overweight and obesity put you at higher risk," Sharma added. "But once the heart disease has set in and they undergo angioplasty or bypass, their outcomes are better."
The study is published July 16 in the journal Mayo Clinic Proceedings.
About two-thirds of American adults are either overweight or obese. A body mass index (BMI) of 25 to 29 is considered overweight; BMIs of 30 and above are classified as obese. BMI is a calculation of body fat based on height and weight.
According to the U.S. Centers for Disease Control and Prevention, about one million coronary artery bypass and angioplasty procedures -- to get around or open blocked heart arteries -- are performed each year. About 70 percent of people undergoing such procedures are overweight or obese, according to study documents.
Examining data collected on tens of thousands of heart patients, Sharma and his colleagues determined that underweight patients (with BMIs under 20) who underwent heart procedures were up to 2.7 times more likely to suffer a heart attack or die over the following 1.7 years.
Conversely, cardiovascular death risk was lower among overweight patients with BMIs between 25 and 30, compared to those with normal BMIs of 20 to 25, the investigators found.
Sharma said several possible reasons explain the discrepancy in survival rates, though scientists aren't certain which are valid. First, overweight patients are more likely to be prescribed cardio-protective medications such as statins and beta blockers than people of normal weight, and at higher doses. Also, heart disease among thinner patients tends to stem from genetic causes, rather than modifiable lifestyle factors such as diet or exercise levels, as it does in overweight patients, he said.
However, the study doesn't directly prove that patients' excess weight was responsible for the survival benefits. It merely found an association between the two.
Dr. William Zoghbi, medical director of Houston Methodist DeBakey Heart & Vascular Center in Texas, pointed out that overweight and obese heart patients included in the new research were about seven years younger than their thinner counterparts. This indicates that they typically developed heart disease at a much younger age than their normal-weight or underweight peers, he said.
"I'm very cautious about drawing strong conclusions from this study," said Zoghbi, also a professor of medicine. "These studies [included in the meta-analysis] were not done to evaluate the effect of various degrees of body mass index, which is important to know."
He said he doesn't see a protective effect of obesity. "It's definitely the wrong message. The message is prevention much more than anything," he said.
The U.S. National Library of Medicine has more about obesity.