Lead author Atif Kukaswadia of Queen's University said the findings are built on a previous cross-sectional study by co-authors and Queen's professors Wendy Craig, Ian Janssen and William Pickett, which showed obese kids were more likely to be involved in bullying.
For the current study published in Obesity Facts, the European Journal of Obesity, researchers looked at a sample of 1,738 students at 16 Ontario high schools in 2006 and 2007. The youths were participants in the Health Behaviour in School-Aged Children Survey.
Youngsters were asked questions about bullying involvement with two specific forms of bullying investigated: physical and relational. Relational bullying refers to excluding or ignoring an individual or spreading false rumours or lies about a person.
Perpetration of physical bullying was assessed through the question: "I hit, kicked, pushed, shoved around, or locked another student(s) indoors."
Self-reported weight and height measurements were calculated to determine body-mass index, or BMI.
Among females who weren't bullied in 2006, Kukaswadia said 14.8 per cent of obese females perpetrated relational bullying in 2007, compared to two per cent of overweight females and 3.8 per cent of normal weight females.
Researchers found approximately two-fold increases in the odds of bullying involvement among obese males as victims and perpetrators of physical bullying.
They conclude that their findings are in line with previous cross-sectional studies confirming obese kids are "at risk for social consequences attributal to their appearance."
"Obese kids do tend to be picked on," said Kukaswadia, a doctoral student with the department of community health and epidemiology.
"When we found that they were also perpetrating the behaviour, that is concerning that they are involved in the behaviour as a victim and as a perpetrator. It's definitely a concern for us."
Kukaswadia said they don't have the data to indicate why obese children may be going the route toward perpetrating acts of bullying.
"We suspect that it's because of the way they're treated by others they then project that behaviour on other people, but we don't know," he said.
Researchers observed that boys were more likely to be bullied physically while girls were more typically involved in relational bullying.
"This may be attributable to perpetrators targeting that which is important to their peer group, with boys valuing physical dominance over their peers and girls valuing close, intimate relationships," they wrote.
Researchers acknowledge limitations in the study. Among them: the small sample size and that few incident cases of bullying which took place. As such, they write that their findings may underestimate the true association between BMI status and bullying behaviour and affect the ability to generalize the study to other youth populations.
Researchers point to evidence that school-based anti-bullying interventions have been effective overall. Such interventions have focused on increasing awareness surrounding bullying behaviours, empowering bystanders and providing support for victims.
Targeting those at high risk for being involved with bullying may increase the effectiveness of those approaches, they write.
"I think the big thing in the report is together with schools, together with teachers, with students, with public health professionals, trying to design programs that take into an account an inclusive school-level approach is the best way to tackle bullying in schools," said Kukaswadia.
Note to readers: This is a corrected story.