CHICAGO: Where a teenage girl sees herself on her school's social ladder may sway her future weight, a study of more than 4,000 girls finds.

Those who believed they were unpopular, gained more weight over a two-year period than girls who viewed themselves as more popular. Researchers said the study showed how a girl's view of her social status has broader health consequences.

The girls in the study were still growing - their average age was 15 - and all of them gained some weight. However, those who rated themselves low in popularity were 69% more likely than other girls to increase their body mass index by two units, the equivalent of gaining about 11 excess pounds. (The body mass index, or BMI, is a calculation based on height and weight).

Girls who put themselves on the higher rungs of popularity also gained some excess weight, but less - about 6 1/2 pounds. Both groups, on average, fell within ranges considered normal. But a gain of two BMI units over two years is more than the typical weight gain for adolescent girls, the researchers said.

"How girls feel about themselves should be part of all obesity prevention strategies," said the study's lead author, Adina Lemeshow, who began the study as a Harvard School of Public Health graduate student. She now works at the New York City Department of Health and Mental Hygiene.

The research, used data from an ongoing study used frequently by scientists studying childhood obesity.

Weight and height data were reported by the girls themselves rather than getting weighed and measured by doctors; that's a weakness in the study that the researchers acknowledged. The researchers took into account the girls' weight and BMI at the start of the study, along with their diet, household income, race/ethnicity and whether they'd reached puberty - and still found the link.

In the study, perceived popularity was measured in 1999 by how the girls reacted to a question next to a picture of a 10-rung ladder: "At the top of the ladder are the people in your school with the most respect and the highest standing. At the bottom are the people who no one respects and no one wants to hang around with. Where would you place yourself on the ladder?"

The researchers put the girls into two groups: the 4,264 who said they were on rung 5 or above, and the 182 who said they were on rung 4 or below. The weight gain link was based on those two groups.

Clea McNeely of Johns Hopkins Bloomberg School of Public Health called the study strong. She said she wanted to know more about the 4% of girls who rated themselves below average in popularity, particularly whether they already were gaining weight faster before they rated themselves as unpopular.

"The reason this paper is so important is it has broader implications beyond weight gain," said McNeely, who was not involved in the research but wrote an accompanying editorial.