Obese people who get surgery to lose weight have half the risk of developing heart failure compared to 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 Dr. Johan Sundstrom of Uppsala University in Sweden.

It’s possible 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 10 kilograms (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 pouch roughly the size of a walnut, 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 46 percent less likely to develop heart failure.

Surgery patients had an average weight loss of 18.8 kg (41.4 lb) more after one year than obese people who instead relied on diet and exercise, the study found. After two years, surgery was associated with an average weight loss of 22.6 kg (49.8 lb) more than 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 current study isn’t a controlled experiment 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.”

For the study, researchers examined data on obese people without a history of heart failure from two national patient registries in Sweden. At the start of the study, patients were typically around 41 years old.

Of nearly 40,000 people in the study, 29 in the diet and lifestyle group and 44 in the surgery group developed heart failure.

Because the surgery group was so much bigger, the actual rate of heart failure for those patients translates to 4.1 cases for every 10,000 people per year in the surgery group and 7.6 cases per 10,000 per year in the lifestyle group, according to the report in Circulation.

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 Dr. 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 Dr. Mary Norine Walsh, a researcher at St. Vincent Heart Center in Indianapolis, Indiana, and president-elect of the American College of Cardiology.

“The take-home message is that weight loss can decrease your risk of developing heart failure down the road,” Walsh, who wasn’t involved in the study, added by email.

Obese patients should be encouraged by the results, said Dr. John Wilkins, a researcher at Northwestern University Feinberg School of Medicine in Chicago who wasn’t involved in the study.

“These data suggest that substantial reductions in weight are most beneficial, but even a modest amount of weight loss – 20 pounds – in obese patients is associated with benefit,”