TUESDAY, June 15 (HealthDay News) -- Obesity is tied to reduced sexual activity and poorer sexual health, according to new research from France.

The rate of unplanned pregnancy among obese women is four times that of normal-weight women, despite the former having fewer partners, the report found.

For men, being obese greatly raised the odds for impotence and their risk of contracting a sexually transmitted disease.

"Being obese has a strong influence on people's sexual life," said lead researcher Nathalie Bajos, an associate professor at the London School of Hygiene and Tropical Medicine and research director at the National Institute of Health and Medical Research, in Paris.

She believes obesity affects the sex lives of women particularly hard.

"Because of social pressure or social stigmatization, obese women are less likely to engage in sexual intercourse and more likely to find sexual partners via the Internet," Bajos said. "Because of their obesity, they are not comfortable meeting men through friends, through work, through parties," she reasoned.

Obese women are also more likely than thinner women to be in a relationship with a partner who is also obese or overweight, Bajos said.

A lot of these problems are driven by the stigmatization of obese women, she said, and "these women are more likely to have low self-esteem."

The report is published in the June 16 online edition of the BMJ.

For the study, Bajos and colleagues collected data on the sexual behavior of more than 12,000 French men and women. Among this group, 3,651 women and 2,725 men were normal weight, 1,010 women and 1,488 men were overweight, and 411 women and 350 men were obese.

Putting on excess pounds did take a toll on sex lives, the study found.

Compared with normal-weight women and men, obese women were 30 percent less likely to have had a sex partner in the past year, while obese men were 70 percent less likely to have had more than one sex partner over the same time, the researchers found.

Obese men were also 2.5 times more likely to experience erectile dysfunction than normal-weight men, and obese men under 30 were more likely to have had a sexually transmitted disease, the researchers found.

Obese women under 30 often didn't seek contraceptive advice or use oral contraceptives, and were more likely to have an unintended pregnancy, the researchers found, and they were also less likely to visit a gynecologist, Bajos said. Due to being overweight, "they do not [always] feel comfortable seeing a gynecologist for contraception issues," she said.

In addition, gynecologists and general practitioners are less likely to prescribe contraception to obese women, Bajos noted. "It could be that they believe these women are less likely to have a sexual life," she said.

The study also found that 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, Bajos said.

Dr. Sandy Goldbeck-Wood is associate specialist in psychosexual medicine at Camden and Islington Mental Health Trust in the U.K., and author of an accompanying editorial. She said that "the differing sexual experiences of obese and non-obese people need cautious interpretation."

"We need to understand more about how obese people feel about their sex lives, and what drives the observed behaviors and attitudes. In particular, we need to know why obese women use less contraception and have more unwanted pregnancies despite having fewer sexual partners," Goldbeck-Wood said. "The answers are likely to be complex, with biological, psychological and social aspects that will require a qualitative research approach," she added.

Doctors must also develop the courage, skill and sensitivity to speak to patients directly about their sex lives and their weight, Goldbeck-Wood noted. "Doctors in primary care and sexual and reproductive health need to pay particular attention to the complex contraceptive needs of obese women," she suggested.

Dr. Robert Schwartz, professor and chairman of family medicine at the University of Miami Miller School of Medicine agreed that, right now, "a lot of physicians don't pay much attention to obese patients' sexuality."

His advice to doctors: "Don't make the assumption that your obese patients are not as sexually active as the rest of the population, and they need to be counseled appropriately."

More information

For more information on obesity, visit the U.S. National Institutes of Health.