NICE, France (June 17) -- Obese women have less sex than women of normal weight, but they also have more unplanned pregnancies because they often don't ask for contraceptives or use the pill, according to a new study.

Obese men have fewer sexual partners than men of normal weight, the study also says, but they run a higher chance of contracting sexually transmitted diseases and are more prone to erectile dysfunction.

The study by French and British researchers, published this week in the British Medical Journal, is the first to investigate the impact of obesity on sexual health.

The results of the study show that the stigma of being fat can lead to less sex but, paradoxically, more complications like unplanned pregnancies, in part because obese women may find it difficult to discuss contraception with their doctors. Experts said the study should be a wake-up call to doctors to overcome their reluctance to discuss delicate subjects like obesity and sex with their patients -- especially women.

"Physicians must talk to obese women about birth control," wrote Dr. Sandy Goldbeck-Wood, a specialist in psychosexual medicine at Ipswich Hospital in Britain, in an editorial accompanying the study.

"Doctors need to get over their own embarrassment and ask the difficult questions. The study lends a familiar slant to a new message: that obesity can harm not only health and longevity, but your sex life," Goldbeck-Wood wrote.

The study centered on sexual activity, sexual satisfaction, accidental pregnancy and abortion and involved telephone interviews with 12,364 French men and women between 18 and 69 who were obese, overweight and of normal weight. Overweight was defined as having a body mass index of between 25 and 30 and obesity as having a BMI of 30.

Professor Nathalie Bajos of France's National Institute for Health and Medical Research directed the study, which comes at a time when obesity is becoming an epidemic in wealthy nations and starting to surface in many developing countries.

"Any temptation to think that obese women are any less sexually active and therefore less in need of effective methods of contraception is clearly without foundation," Bajos said.

Among the key findings in the study:

• Obese women have four times the number of unplanned pregnancies compared with women who are not obese, even while they have a less active sex life.
• Obese women under 30 are much less likely to ask for contraceptives or use the pill.
• Obese men are at more risk of contracting a sexually transmitted disease, even though they have fewer sex partners.
• Obese and overweight men are more likely to suffer from erectile dysfunction, but sexual dysfunction was not found to occur any more in obese and overweight women than in their slimmer counterparts.
• Obese women were five times more likely to meet sex partners on the Internet and more likely to watch pornography. Yet they were less likely to view sex as important in their lives.