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

Those who believed they were unpopular tended to gain more weight over a two-year period than girls who viewed themselves as more popular.

Girls who rated themselves low in popularity were 69 percent 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 Adina Lemeshow, lead author of the study appearing in January's issue of Archives of Pediatrics & Adolescent Medicine.