Previous research has tended to focus on the role that diet plays in women diagnosed with or receiving treatment for infertility.
Women who eat less fruits and more fast food take longer to get pregnant and are less likely to conceive within a year, a study has found.
Researchers asked 5,598 first-time mothers about their diet. Compared to women who ate fruits three or more times a day in the month before conception, women who ate fruits less than one to three times a month took half a month longer to become pregnant.
Similarly, compared to women who never or rarely ate fast food, women who consumed fast food four or more times a week took nearly a month longer to become pregnant.
Among all the couples in the study, 468 (8 per cent) were classified as infertile (defined as taking longer than a year to conceive) and 2,204 (39 per cent) conceived within a month.
When the researchers looked at the impact of diet on infertility, they found that in women with the lowest intake of fruit, the risk of infertility increased from 8 per cent to 12 per cent, and in those who ate fast food four or more times a week, the risk of infertility increased from 8 to 16 per cent.
"These 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," said Claire Roberts, from the University of Adelaide in Australia, who led the study published in the journal Human Reproduction.
"We recommend that women who want to become pregnant should align their dietary intakes towards national dietary recommendations for pregnancy. Our data show that frequent consumption of fast foods delays time to pregnancy," said Jessica Grieger, post-doctoral research fellow at the University of Adelaide.
Previous research has tended to focus on the role that diet plays in women diagnosed with or receiving treatment for infertility; the impact of maternal diet before conception in the general population has not been widely studied.
During the first antenatal visit at around 14-16 weeks' gestation, midwives collected information about the time it took to become pregnant and the women's diet.
This included details of their diet in the month before conception, and how frequently they consumed fruit, green leafy vegetables, fish and fast foods. Fast foods included burgers, pizza, fried chicken and chips that were bought from take-away or fast food outlets.
Fast foods eaten at home (bought from supermarkets, for example) were not included in the data collected and so consumption of this type of food is likely to be under-reported.
"We adjusted the relationships with pre-pregnancy diet to take account of several factors known to increase the risk of infertility, including elevated body mass index (BMI) and maternal age, smoking and alcohol intake," Grieger said.
"As diet is a modifiable factor, our findings underscore the importance of considering preconception diet to support timely conception for women planning pregnancy," he said.
The researchers also found that while intake of fruit and fast foods affected time to pregnancy, pre-pregnancy intake of green leafy vegetables or fish did not.