If you’ve ever been overweight or obese, and felt that your sex life left something to be desired, a new study finds that you’re not alone. Obese participants report fewer partners, more sexual dysfunction, less use of contraception, and more unplanned pregnancies.

Nathalie Bajos and her team gave surveys to over 10,000 participants; just over 60% were normal weight, meaning that their body mass indexes (BMI) fell within the normal range, 18.5-25. Also surveyed were 1010 women and 1488 men who were overweight (BMI of 25-29), and 411 women and 350 men who were obese, with BMIs over 30.

Another interesting trend was that younger obese women (under 30) were 73% less likely to go to a health provider for contraceptives and 70% less likely to use the pill, compared to normal weight women... Obese women under 30 also reported unplanned pregnancies four times as often as normal weight women.

The results showed that compared to normal weight participants, obese men were 70% less likely to have had more than one sex partner in the previous 12 months, and obese women were 30% less likely to have had one sex partner in this time period. Obese men were also 2.6 times as likely as normal weight men to report erectile dysfunction. Interestingly, obese women did not report any more sexual dysfunction than normal weight women, and were just as likely to live with a sexual partner. But the researchers say that, overall, as BMI rose, the likelihood of having a sexual partner fell for both sexes.

Another interesting trend was that younger obese women (under 30) were 73% less likely to go to a health provider for contraceptives and 70% less likely to use the pill, compared to normal weight women. They were also “eight times more likely to use less effective methods, such as withdrawal, compared with women with normal BMI.” Obese women under 30 also reported unplanned pregnancies four times as often as normal weight women.

Obese women had about the same likelihood of reporting having had a sexually transmitted disease in the past five years, but obese men under 30 were more likely than normal weight men to report an STD. Obese women were also more likely to look to the internet for sexual partners, and also more likely to watch pornography.

The authors make the interesting observation that men and women differed in how they viewed themselves and the significance of sexuality: “There was also evidence that self image varies with gender; obese women were twice as likely to see themselves as such compared with obese men. They also downgraded the importance of sexuality to their wellbeing, which might reflect a rationalising adjustment to the lack of an available sexual partner.”

The authors talk about the societal factors that may be at play here, like the pressure that many women in industrialized countries feel to be thin, as well as other potential causes: “Psychological factors (such as poor sexual self esteem leading to difficulty in allowing or initiating sex) or biological factors (such as musculoskeletal problems) might also be involved.” They also raise concern at the public health issue of obese women being less likely to use effective – or any – method of contraception and reporting more unwanted pregnancies, which is of particular concern since obese women are also at higher risk for prenatal health problems.

The authors conclude that health professionals should be aware of the role of weight in sexual health, and say that “[g]iven the social and gender related sensitivities, obese women and men will certainly benefit from tactful guidance and advice on preventive sexual health matters.”

Bajos is affiliated with the London School of Hygiene and Tropical Medicine; the findings are reported in the June 16, 2010 online issue of BMJ.