In the study, scientists looked at 22,400 people taking part in a large, international online weight-management program. They focused on about 5,400 people who participated in the program for at least six months and who posted their weight loss progress at least twice during the study period.

The researchers found the most significant factor linked to weight loss was a person’s level of social networking. After six months, people who did not have any friends in the online community saw a 4.1 percent decrease in their body weight, on average. On the other hand, those in clusters made up of two to nine friends experienced a 5.2 percent decrease in body weight. The people who were in the largest cluster of friends within the network, which was made up of nearly 1,500 members, saw a 6.8 percent decrease in body weight. Those who were deeply embedded in the social network — who not only had a high number of friends, but also whose friends each also had a high number of friends — experienced a 8.3 percent decrease in body weight.

Study lead, Poncela-Casasnovas said “It has been known for a while that in-person support groups and interventions can help with obesity problems, but it had never been shown before that an online system can achieve a similar thing, but at a way lower cost,”.

As for people who don’t have connections in these communities, or only have a few, “we suggest that isolated people in the program should try to reach out and make friends, to benefit from the connectedness-weight-loss effect,” Poncela-Casasnovas said. “An intervention within the program could be implemented to suggest friends to the users, similar to what other famous social networking sites do.”