Obese people who get surgery to lose weight have half the risk of developing heart failure as do patients who make lifestyle changes to shed excess pounds, a recent study suggests.

“We were surprised by the large difference in heart failure incidence between the two groups,” said lead study author Johan Sundstrom of Uppsala University in Sweden.

It’s possible that gastric bypass patients had a lower risk of heart failure because they lost more weight than the group trying to do so without surgery. Researchers also found that losing 22 pounds by any means was tied to a 23 percent drop in heart failure risk.

The study team examined data on 25,805 obese people who had gastric bypass surgery, which reduces the stomach to a small pouch, and 13,701 patients who were put on low-calorie diets. After following half of the patients for at least four years, people who had gastric bypass were found to be 46 percent less likely to have developed heart failure.

After one year, surgery patients had an average weight loss 41.4 pounds greater than that of those who relied on diet and exercise, the study found. After two years, surgery was associated with an average weight loss that was 49.8 pounds more than those who undertook lifestyle changes.

Some previous research has linked obesity to heart failure, and a growing body of evidence suggests that obesity might directly cause the heart condition, Sundstrom said. While the new study wasn’t designed to prove a causal relationship, it adds more evidence in support of this possibility.

“Obesity may increase the risk for heart failure through the smorgasbord of conditions that accompany obesity, such as high blood pressure, high blood lipids, diabetes” and rapid irregular heartbeat,” Sundstrom said by email. “Bariatric surgery has been associated with lower incidence of all of these risk factors.”

“There is also some evidence that obesity per se may cause heart failure, a condition sometimes called obesity cardiomyopathy,” Sundstrom said. “From that perspective, weight loss may preserve cardiac function by reducing the heart’s pump demand and stress.”

It’s possible that factors not included in the data influenced how much weight people lost or whether they developed heart failure, the authors note.

Heart failure tends to afflict the old, and the study of younger adults may not have followed patients long enough to fully understand the impact of surgery on the heart, said Sheldon Litwin of the Medical University of South Carolina in Charleston.

“Most patients undergoing bariatric surgery are relatively young; they are at pretty low risk of developing heart failure even if they are obese,” Litwin, who wasn’t involved in the study, said by email.

Even so, the study covers new ground and helps establish a connection between weight loss and a reduced risk of heart failure, said Mary Norine Walsh, a researcher at St. Vincent Heart Center in Indianapolis and president-elect of the American College of Cardiology.