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CORVALLIS, Ore. - Oregon and Hawaiian researchers have found that a woman's weight does not seem to affect sexual behavior. In fact, overweight women are more likely to report having sex with men than women considered to be of "normal weight."

The study, published in the September issue of Obstetrics & Gynecology, is based on data from the 2002 National Survey of Family Growth that looked at sexual behavior of more than 7,000 women. Dr. Bliss Kaneshiro, an assistant professor at the School of Medicine at the University of Hawaii, was a student at Oregon Health & Science University at the time. Oregon State University professor Marie Harvey helped Kaneshiro with her research because of Harvey's background and expertise in women's sexual and reproductive health issues.

Some studies have suggested that obese and overweight women have a higher risk of unintended pregnancy than do normal weight women, according to Kaneshiro. Although multiple factors, including contraceptive use and its efficacy, may increase the risk of unintended pregnancy among these women, sexual behavior and the frequency of intercourse could also be a factor.

Kaneshiro's objective was to study the impact of body mass index on sexual behavior. It is important to understand this relationship because preexisting physician biases can affect how heavy women are counseled about pregnancy and sexually transmitted diseases prevention. Kaneshiro studied the relationship between body mass index and sexual behavior, including sexual orientation, age at first intercourse, number of partners, and frequency of intercourse.

"Our analysis demonstrated that obese and overweight women do not differ significantly in some of the objective measures of sexual behavior compared to women of normal weight," said Kaneshiro. "This study indicates that all women deserve diligence in counseling on unintended pregnancy and STD prevention, regardless of body mass index."

The study seems to contradict widely held stereotypes that overweight and obese women are not as sexually active as other women. If anything, the researchers concluded the opposite seems to be true.

"I was glad to see that the stereotype that you have to be slender to have sex is just that, a stereotype," Harvey said.

Kaneshiro said the data showed that overweight women were more likely to report having sexual intercourse with a man, even when she controlled for age, race and type of residence. Ninety-two percent of overweight women reported having a history of sexual intercourse with a man, as opposed to 87 percent of women with a normal body mass index.

"These results were unexpected and we don't really know why this is the case," Kaneshiro said.

Harvey said the important part to take away from the study is that physicians and others who work in women's medical health should never make assumptions about sexual behavior based on outward appearances.

"Some medical practitioners may not do appropriate follow-up with women who are overweight, they might assume they aren't having sex unless they are told otherwise," Harvey said.

Other coauthors on the study include Jeffrey Jensen, Mark Nichols and Alison Edelman of Oregon Health & Science University and Nichole Carlson of the University of Colorado Denver.

Kaneshiro's study was awarded first prize at the American College of Obstetricians and Gynecologists' annual meeting this year. The abstract can be viewed at: http://www.greenjournal.org/cgi/content/abstract/112/3/586.