An unplanned pregnancy is four times more likely to happen for single women who are obese, researchers have revealed.
The largest ever study into obesity and sexual health found that obese women generally view sex as less important and are five times more likely to have met their partner on the internet.
It also found that they are 66% less likely to take the Pill and 63% less likely to seek advice on contraception. Obese women are also more likely to have a partner who is obese than women of a healthy weight.
They are 29% less likely to report having a sexual partner in the previous year.
However, obesity also impacts men, with obese men being 69% less likely to report more than one partner in the previous year compared with men of normal weight.
The study found they were almost three times more likely to report erectile dysfunction than men of a normal weight and more likely to say they have a sexually-transmitted infection.
The research, published online in the British Medical Journal, involved more than 12,000 men and women in France.
But a British expert said the findings had far-reaching implications, and called for greater understanding of how obese people feel about their sex lives and the impact of obesity on health.
In an accompanying BMJ editorial, Dr Sandy Goldbeck-Wood at the Camden and Islington Mental Health Trust in London said: "In particular, we need to know why obese women use less contraception and have more unwanted pregnancies despite having fewer sexual partners."