A University of Pittsburgh School of Medicine study says thin and overweight adolescent girls are more likely than girls of normal weight to engage in risky sexual behavior.

Study results also indicate that a girl's race or ethnicity, as well as her actual or perceived weight, play a role in what risky sexual behaviors she participates in.

The study, conducted by Dr. Aletha Akers, assistant professor of gynecology and reproductive sciences in the medical school, found girls who were sexually active and overweight based on body-mass index (BMI), or thought they were overweight, are less likely to use condoms than normal-weight, sexually active girls. Underweight girls also were less likely to use condoms.

"A couple of other studies were done with young adult women and college-age women concerning weight and sexual behavior, but those studies showed variations," Dr. Akers said, noting her study focused exclusively on adolescent girls. "No one [before this study] showed what role race might play in this."

Published online in the November issue of Pediatrics, the study is based on the 2005 Youth Risk Behavior Surveillance survey, which showed that half of the 7,300 adolescent girls surveyed reported having sex.

In Dr. Akers' study, Caucasian girls who believed that they were underweight, whether accurately or not, were more likely to have had sex and to have had four or more sexual partners.

Overweight Caucasian girls, meanwhile, were less likely to use condoms.

The reverse held true for African-American girls.

Underweight African-American girls were less likely to use condoms while overweight African-American girls reported to be more likely to have had four or more sexual partners.

The study found that Latina girls, regardless of their weight or perceived weight, were more likely to engage in a wide variety of risky behaviors, including sex before age 13, greater than four sexual partners and use of alcohol.

But Dr. Akers cautioned against drawing conclusions about Latina girls. She said the sample of Latina girls was small among the 7,300 high-school girls surveyed about sexual activity and risky sexual behavior. The Latina category also included a broad range of girls of different national origin and diverse cultures throughout the Americas and Europe. Those factors make it difficult to draw conclusions about the Latina population.

But in the discussion of the study results, Dr. Akers hypothesized that thin Caucasian girls and overweight African-American girls had more sexual partners because those body images are preferred or most desirable in their respective cultures. If so, those girls have more opportunities for sexual relationships, possibly explaining why they were more likely to have had four or more partners.

On the contrary, thin African-American girls and overweight Caucasian girls -- or those who perceive themselves to fit those weight categories -- might feel less desirable based on social norms for attractiveness. Dr. Akers hypothesizes that those groups of girls might be less willing to use condoms or capable to negotiate condom use.

"The goal is the point out that race is an important context of how girls think about their body image, and those variations influence how they negotiate sexual behavior," Dr. Akers said.

While her study shows a relationship between race, body image and sexual behavior, the study does not explain why such relationships actually occur.

For that reason, Dr. Akers said she'll seek funding through the National Institutes of Health to conduct a follow-up study focused on understanding why different body types in different ethnic and racial cultures produce varying behaviors.

Results of the second study could be used in sex or reproductive-health education classes to reduce risky sexual behavior among adolescent girls.

Richard Baird, president and chief executive officer of Adagio Health, a nonprofit organization that provides family planning and reproductive health education, among other services in 23 counties in Western Pennsylvania, cautioned against using the study to prejudge girls or generate biases.

He and Mary Anne Poutous, Adagio director of community education, said they intended to read the entire study before commenting at length about it.

"We are a long way from having information that's useful for risk avoidance or for counseling intervention," Mr. Baird said.

Ms. Poutous said the study, at least at this stage, shouldn't be used to change sound intervention practices or counseling methods for adolescent clients. Both also said factors other than body type can affect self esteem in adolescents and prompt other risky behavior, including smoking and alcohol use. They expressed interest in reading any follow-up studies, as well.

Dr. Akers also discouraged using study results to bolster racial or ethnic stereotypes. The degree of sexual activity among adolescent girls is similar in all Western cultures, she said, and fairly consistent year after year. In that context, cultural preferences for particular body types do influence sexual behavior among adolescent girls.

"Studies in adult women have shown a relationship between weight and sexual behaviors," Dr. Akers said. "Our study adds to the body of literature by showing these relationships start early in adolescence when girls are forming and beginning to engage in dating and sexual relationships."

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