A new study out of the Yale Center for Interdisciplinary Research on AIDS found a clear link between risky sex and women's body mass index (BMI).
The study followed over 700 mothers between 14 and 25-years-old in New Haven and Atlanta for six months to a year. These women reported their sexual history and condom use regularly.
In this group, overweight women were found to have riskier sex, exposing themselves to STIs at a higher rate than average weight or obese women. However, obese women were significantly less likely to catch an STI than normal weight women.
Perhaps most surprisingly is that all of the women reported similar rates of protected and unprotected sex. Researchers think that these women's weight may have impacted the type of partners they had sex with.
Previous work by the same group found that obesity and the risk of catching an STI increased for young mothers. Researchers assumed the risk of STIs would drop as weight increased because other studies have shown that overweight women are less sexually active than normal weight women. This was not the case.
For now, these results are surprising but they don't offer a clear relationship between STI rates and weight. Also, there are several key factors that prevent the results from being applied to the larger population. The majority of the women in the study were young mothers between 14 and 25, lived in urban areas, and were African-American or Hispanic.