THURSDAY, July 12, 2012 (HealthDay News) -- Worried about the battle of the bulge? Your circle of friends might be key to your weight gain, a new study suggests.
The research, conducted among high school students, found that teens were more likely to pile on the pounds if they hung out with people who were already heavier than they were. The opposite was true for students whose friends were thinner, however.
The researchers say the findings might help experts combat obesity, at least among teenagers.
"These results can help us develop better interventions to prevent obesity. We should not be treating adolescents in isolation," study author David Shoham, an assistant professor in the department of preventive medicine and epidemiology of Loyola University Chicago Stritch School of Medicine, said in a Loyola news release.
In conducting the observational study, the researchers were trying to figure out if obesity clusters in groups of friends due to social influences (when friends influence one another) or if people simply seek out the friendship of people who are most similar to themselves, including weight status.
To answer this question, the researchers examined information previously collected from students at two large high schools over the course of two school years. One school, known as Jefferson High, was located in a rural area and had a mostly white student population. The second school, called Sunshine High, was located in a city and had a more racial and ethnically diverse student body.
The researchers applied a statistical technique to analyze survey responses from more than 600 students from Jefferson High and 1,151 students from Sunshine High. The teens were asked about their weight, friends, sports and the amount of time they spent in front of the TV or computer or playing video games. The researchers also calculated the students' body mass index (a measure of height and weight).
The way that students initially chose their friends did play a role in how obesity clustered within social groupings. The researchers pointed out, however, that even after taking this finding into account there was still a significant link between obesity and a student's circle of friends, suggesting that friend-to-friend influences might also be key.
For example, a Jefferson High student with thin friends had a 40 percent chance of losing weight and a 27 percent chance of gaining weight. On the other hand, the researchers found a student who was close to being overweight and had obese friends had only a 15 percent chance of losing weight but a 56 percent chance of gaining more weight.
The bottom line: A person's social networks must be taken into consideration when developing strategies to prevent or treat obesity among teenagers, the researchers said.
Shoham's team said the study was limited by its reliance on self-reported data and the inability to directly test how friendships are formed and maintained. They added that the study's data were also collected more than a decade ago -- before the advent of Facebook and the sharp rise in rates of childhood obesity.
Since it is observational in nature, the study can only show an association between friends and weight gain; it cannot prove a cause-and-effect relationship. And, "of course, no one study should ever be taken as conclusive and our future work will attempt to address many of these limitations," Shoham said.
The study was published recently in the journal PLoS ONE.
The U.S. Centers for Disease Control and Prevention provides more information on obesity.