Women who consume fast food four or more times a week are more likely to suffer infertility, according to a new Australian study published in a leading reproductive medicine journals.
The research, carried out by the University of Adelaide's Robinson Research Institute and published in Human Reproduction, found women fell pregnant sooner if they consumed a good-quality diet – which included very little fast food and plenty of fruit – while trying to conceive.
The study involved 5598 women in Australia, New Zealand, the UK and Ireland.
The first-time mothers were interviewed by midwives during their first antenatal visits, and were asked about their eating habits in the month leading up to their pregnancies.
The institute's Claire Roberts led the study, which found women who consumed fast food four or more times a week took nearly a month longer to become pregnant than those women who rarely if ever ate fast food.
The study also found women who ate fruit less than one to three times a month took two weeks longer to get pregnant than women who ate fruit three or more times a day before conception.
"The findings show that eating a good-quality diet that includes fruit and minimising fast-food consumption improves fertility and reduces the time it takes to get pregnant," Professor Roberts said.
Eight per cent of the women in the study were classified as infertile (not pregnant after one year of trying to conceive), while 39 per cent conceived within a month of trying.
When the researchers looked at the impact of diet on infertility, they found the women with the lowest intake of fruit were more likely to be infertile (12 per cent compared with 8 per cent overall), while those who ate fast food four or more times a week were twice as likely to be infertile (16 per cent compared with eight per cent).
One of the study's authors, Jessica Grieger, says the data shows that frequent consumption of fast foods delays pregnancy.
"We recommend that women who want to become pregnant should align their dietary intakes towards national dietary recommendations for pregnancy. Our data shows that frequent consumption of fast food delays time to pregnancy," Dr Greiger said.
The researchers also found that while intake of fruit and fast foods affected the time it took to conceive, pre-pregnancy intake of green, leafy vegetables or fish did not appear to have any impact.
The researchers now hope to identify if any particular dietary patterns, rather than individual food groups, may be associated with a woman's fertility.
Dietitian Melanie McGrice, of St Vincent's Hospital in Melbourne, says the new research supports the growing body of evidence that adopting a nutritious diet is one of the most important ways couples can optimise their fertility.
"I'd like to see all GPs and fertility specialists referring [patients] to a fertility dietitian prior to conception," she says.
"As a fertility dietitian, I'm seeing more and more women who incorrectly think that they should be avoiding fruit in an effort to help them conceive. This study demonstrates that fruit consumption is not only safe, but beneficial for most women to optimise their fertility.
"Fruit is rich in antioxidants, vitamins and phytochemicals, and should not be lumped into the same basket as sugar and soft drinks."
Dr Jemma Evans, of the Hudson Institute of Medical Research in Victoria, says the study clearly highlights the need for a greater understanding of the impact of diet before conception on fertility and pregnancy.
"It also paves the way for accurate pre-conception dietary assessment studies using daily food records to fully understand the impact of lifestyle choices on fertility," Dr Evans says. Belinda Connolly, a food blogger who runs the website The Hungry Mum, says she adhered to a very healthy diet before she and her husband tried for their first baby.
"I have been a vegetarian since I was about 15 but I always ate dairy and eggs," she says.
"I upped my dairy quotient when I was trying to conceive and I have never really eaten much fast food anyway.
"I would have the occasional vegetarian pizza, say three or four times a year, hot chips from a takeaway maybe four times a year and Thai takeaway a few times a year."
Ms Connolly says she fell pregnant with her first child within three months of trying, and even less with her second child.
She says she felt lucky that she had no problems getting pregnant but never really considered the role of her diet until now.
However, she says her fruit intake cannot get any credit for the ease in which she conceived.
"I have never really liked fruit. I maybe eat it twice a month."