A good way to boost your chances of pregnancy?

Harvard researchers found women who frequently ate these foods were 85% more likely to have ovulation problems.

In contrast, the Human Reproduction study found eating full-fat dairy foods, including ice cream, cut the risk of this type of infertility.

However, UK experts insist there is scant evidence of a link.

The research used a database of 116,000 US nurses which is regularly updated with information about their lifestyle, diet and health.

I'm not convinced that there is any reason for women who are trying to conceive to alter their diet, unless they are obese

Dr Richard Fleming

Glasgow Centre for Reproductive Medicine

They were asked whether they had been trying, and failing, to conceive, and whether a diagnosis of 'ovulatory failure' - infertility due to irregularity in the normal monthly cycle - had been made.

Over an eight year period between 1991 and 1999, 438 women reported this set of circumstances, and their answers to questions about their diet were analysed.

If the women ate two or more portions of low-fat dairy produce a week, the risk of infertility due to ovulatory failure appeared to be 85% higher.

When women eating two or more portions of full-fat dairy produce such as whole milk or ice cream were compared with those eating one or fewer, they had a 27% lower risk of infertility due to lack of ovulation.

Food swap

Dr Jorge Chavarro, who led the project, said that the link needed further investigation.

He said that women trying to conceive should think about their diet: "They should consider changing low-fat dairy foods for high-fat dairy foods; for instance, by swapping skimmed milk for whole milk and eating ice cream, not low fat yoghurt."

He believes the key may be that there is a substance vital for healthy ovarian function that requires the presence of fat for it to be properly absorbed into the body.

However, other scientists say that the only compelling evidence of a link between diet and infertility involves obesity, which is linked to a significant reduction in the chances of conception.

Dr Richard Fleming, from the Glasgow Centre for Human Reproduction, pointed out that women reporting a low-fat 'healthy' diet might be those already aware of fertility issues and trying to improve their chances.

He said: "Women with ovulatory failure make up a relatively small proportion of cases of female infertility.

"I'm not convinced that there is any reason for women who are trying to conceive to alter their diet unless they are obese, and I would not advise any woman to do this."