Though not enough to cancel out that "Freshman 15," having an overweight roommate in college might keep you slimmer, a new study suggests.

The research showed college women who bunked with individuals who weighed more than average gained a half pound during their freshman year compared with the average 2.5 pounds gained by those with thinner roommates.

Freshmen typically gain an average of between 2.5 and 6 pounds (1.1 and 2.7 kg) – much less than the mythical 15, the researchers pointed out.

"This finding seems counterintuitive, but there are some good explanations for why it may be happening," said study researcher Kandice Kapinos, an assistant research scientist at the University of Michigan Institute for Social Research.

Behavior could explain the link since, Kapinos said, heavier roommates are more likely than average-weight women to diet and exercise more often. They are also more likely to use weight-loss supplements and purchase college meal plans that limit access to food, Kapinos added.

"It's not really the weight of your roommate that's important, but the behaviors your roommate engages in," Kapinos said. "These behaviors are what may really be 'contagious.'" [See "Obesity Is Socially Contagious")

For the current study, which was presented this summer at the annual meeting of the American Society of Health Economists and announced this week, the researchers assessed 144 female college students randomly assigned to share a living situation during their freshman year. At the start of the fall semester, the researchers obtained the women's weight and height, and asked about weight-management behaviors, including whether they had tried to lose weight during the previous year, how often they exercised, and whether they had signed up for an unlimited college meal plan.

Later this fall, the researchers will expand their study to include a larger sample of students at a public university to see if roommate weight patterns persist. They will also examine other environmental influences and see if the findings vary with race, ethnicity or socioeconomic status.

"Our hope is that this line of research will have practical implications for university administrators and more generally for public health efforts aimed at reducing obesity," Kapinos said.

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