By Amy Norton
The study, of more than 3,500 heart failure patients, is the latest to look into the so-called "obesity paradox." The term refers to a puzzling pattern that researchers have noted for years: Obese patients with heart disease tend to survive longer than their normal-weight counterparts.
"It has consistently been observed in large studies," said Dr. Gregg Fonarow, co-chief of cardiology at the University of California, Los Angeles. "But the mechanisms contributing to this paradox continue to be debated."
Fonarow was not involved in the new research, but has worked on studies reaching similar conclusions.
The pattern is dubbed a "paradox" because obesity actually raises your risk of developing heart disease in the first place.
So it's not clear, Fonarow said, why it would be linked to better survival after the disease develops.
In the current study, South Korean researchers followed 3,564 patients who were hospitalized with heart failure symptoms. Overall, about 2,000 were overweight or obese, while more than 1,500 were of normal weight.
Heart failure is a chronic condition in which the heart muscle can no longer pump blood efficiently enough to meet the body's needs. It causes symptoms such as breathlessness, fatigue and fluid buildup.
In general, the study found, heavier patients tended to show less deterioration in the structure and function of the heart's main pumping chamber.
And the highest survival rate was seen among overweight or obese patients who were metabolically healthy -- meaning they did not have high blood pressure, high cholesterol or abnormal blood sugar levels.
Among those patients, more than 79 percent were still alive three years later. That compared with 64 percent of normal-weight patients in good metabolic health.
Patients in the normal-weight group who were metabolically unhealthy fared worst: Only 55 percent were still alive after three years. Metabolically unhealthy obese people fared about the same as normal-weight, metabolically healthy people -- with a survival rate of about 66 percent.
However, it was apparently not easy to be overweight and metabolically healthy: Only 12 percent of overweight/obese patients were, said researcher Dr. Chan Soon Park.
Park, of Seoul National University Hospital, was scheduled to present the findings this week at a meeting of the European Society of Cardiology, in Milan, Italy.
What do the results mean? They do not prove that obesity, itself, provides a survival advantage, said Dr. Gurusher Panjrath.
Panjrath, who was not involved in the research, chairs the American College of Cardiology's heart failure and transplant section.
He noted that the study -- like most previous ones -- used body mass index (BMI) to divide patients into weight categories.
People with a BMI of 23 or higher were considered "overweight/obese," while those with a lower BMI were considered "normal-weight." For example, a 5-foot-8-inch person who weighs 151 pounds has a BMI of 23. (The definitions used for Asian populations are different from those used in the United States and elsewhere, Park said.)
But BMI -- a measure of weight in relation to height -- is an imprecise gauge, Panjrath explained.
He said the normal-weight group in this study might have included some patients who were actually more sick and frail. In contrast, people who had more muscle, and may have been relatively fitter, could have fallen into the overweight category.
In fact, Panjrath said, a number of studies have suggested that cardiovascular fitness levels -- rather than weight -- are critical to heart disease patients' outlook.
That includes heart failure.
Often, people develop heart failure after suffering a heart attack that damages the heart muscle, or because of poorly controlled high blood pressure.
Obesity is a risk factor because it contributes to the conditions that can cause heart failure, Panjrath explained. There's also some evidence those extra pounds might directly affect heart muscle function, he said.
Once people are diagnosed with heart failure, Panjrath said, the priority is to boost their fitness levels through exercise, and control conditions like high blood pressure and diabetes.
"Fitness is more important than fatness," Panjrath said. He added, though, that weight loss is encouraged when patients are severely obese.
Park said that since weight loss can be difficult, efforts to improve factors like blood pressure and fitness may be more practical.
Research presented at meetings should be considered preliminary until published in a peer-reviewed medical journal.