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In high school, they say birds of a feather flock together, but is that really the case? A Loyola study is suggesting that.

According to researchers, a person's circle of friends may influence his or her weight. The researchers examined data from almost 2,000 students from two different high schools. Previously, researchers not affiliated with the current study asked students about their weight, friendships, sports activities and screen time. The body size measure they used was body mass index (BMI), which is calculated from a student's height and weight. A BMI over 25 is considered overweight and a BMI over 30 is considered obese.

Researchers concluded that students were more likely to gain weight if they had friends who were heavier than they were. Conversely, students were more likely to get trimmer -- or gain weight at a slower pace -- if their friends were leaner than they were. Additionally, a student's face-to-face interactions also influences how active he or she is in sports.

According to David Shoham, one of the study's authors, the new findings can help with the fight against obesity.

"These results can help us develop better interventions to prevent obesity," Shoham said. "We should not be treating adolescents in isolation."

Researchers found the way friends are selected is part of the reason why obesity clusters in social circles. They say if a borderline overweight student had slim friends - average BMI 20- there was a 40 percent chance the student's BMI would drop in the future and a 27 percent chance it would increase. But if a borderline overweight student had obese friends - average BMI 30 - there was a 15 percent chance the student's BMI would decrease and a 56 percent chance it would increase.

Although more research needs to be done to factor in the emergence of online social networking sites like Facebook and the increasing obesity rates, Shoham believes these results add to the vigorous debate over the relative importance of selection and peer influence in network studies of health.

"Our results support the operation of both homophily and influence," said Shoham. "Of course, no one study should ever be taken as conclusive and our future work will attempt to address many of these limitations."

The findings are published in the journal PLoS ONE.