The researchers found that compared to women who ate three or more portions of fruit in the month before conception, those who ate fruit less than one to three times a month took around two weeks longer to become pregnant.
The findings were published in the journal Human Reproduction on May 4.
Researchers also found an average month-long delay in women who consumed fast food four or more times a week, unlike those who never or rarely ate fast food. "This new research supports the growing body of evidence that a nutritious diet is one of the most important strategies that a couple can employ to optimise their fertility", said Ms McGrice.
Specifically, the study pinpointed the exact amount of fast food meals that impact pregnancy.
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Fast food consumers were at slightly higher risk of having fertility problems, but this was based on a very small subset of women who took longer than 12 months to conceive. This was compared to women who ate more fruit instead of fast food.
"The major finding is that the risk of infertility - that is, taking longer than 12 months to conceive - went from 8 percent for all the women in the cohort to 12 percent ... in women with the lowest fruit intake", said lead study author Claire Roberts, a senior research fellow at Robinson Research Institute at the University of Adelaide in Australia.
Dr. Jessica Grieger, post-doctoral research fellow at the University of Adelaide and co-author of the study said: "We recommend that women who want to become pregnant should align their dietary intakes towards national dietary recommendations for pregnancy".
The study presented here was conducted at the between 2004 and 2011 at the multi-centre Screening for Pregnancy Endpoints (SCOPE).
Being too thin or being overweight can impact a woman's fertility.
"It is in keeping with other pieces of research, which show that your overall dietary pattern may influence fertility", Mathur told Live Science. 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. First, the researchers admitted that they relied heavily on retrospective recall about what the female participants ate. "Fast foods are energy dense with high amounts of saturated fat, sodium and sugar".