Heart-healthy lifestyles can be contagious to your family and friends.

In a late-breaking clinical trial presented at the American Heart Association’s Scientific Sessions 2013, people in social networks who received an intervention to tackle their weight problems together lost an average 6½ pounds more and trimmed an extra 1¼ inches from their waists compared with those who received standard individual care.

The social network intervention also led to 4 to 5 mmHg drops in systolic and diastolic blood pressure. Benefits lasted beyond the 10-month program up to even six months after.

Researchers assigned groups of two to eight friends and family members per group into “microclinic” social network clusters to attend weekly social and health activity sessions focused on physical activity, nutrition and health education for 10 months in rural Kentucky, where medical care is limited and rates of obesity, diabetes and heart disease are high.

Among the 552 participants — 85.8 percent women and an average 51 years old — about 80 percent were obese. Average body mass index at enrollment was 36.2, regarded as morbidly obese.

“Leveraging the social network and peer influences and social networks for support may be important for fighting obesity,” said Eric L. Ding, Sc.D., epidemiologist and nutritionist at the Harvard School of Public Health and director of epidemiology at Microclinic International. “We need to focus on more than the individual obese patient in isolation, and look to family and friend networks and the communities where people live.”

Clusters of friends and family can help establish and spread healthy norms, such as regularly checking weight and blood sugar (if diabetic), exercising, watching calories, and eating fresh fruits and vegetables, he said.

In a subgroup retested at 16 months, a substantial majority of the decrease in weight, waist size and blood pressure were maintained.

“Most weight loss programs do not have sustained weight loss beyond one year,” Ding said.