Eating ice cream and drinking whole fat milk appears to be beneficial for women trying to become pregnant, but a diet consisting of low-fat dairy products such as skimmed milk and yoghurt is not, according to new research.

Researchers in the US have found a link between a low-fat dairy diet and increased risk of infertility due to lack of ovulation (anovulatory infertility). Their study showed that women who ate two or more servings of low-fat dairy foods a day increased their risk of ovulation-related infertility by 85%. On the other hand, women who ate at least one serving of high-fat dairy food a day reduced their risk of anovulatory infertility by more than a quarter.

Lead author of the study, Dr Jorge Chavarro, advised women wanting to conceive to change 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."

However, he said that it was important that women did this within the constraints of maintaining their normal calorie intake and limiting their overall consumption of saturated fats in order to maintain general good health. "Once they have become pregnant, then they should probably switch back to low-fat dairy foods as it is easier to limit intake of saturated fat by consuming low-fat dairy foods," he said.

The researchers believe that the presence of a fat-soluble substance, which improves ovarian function, might explain the lower risk of infertility from high-fat dairy foods. "The intake of dairy fat, or a fat-soluble substance present in dairy foods, may partly explain the inverse association between high-fat dairy foods and anovulatory infertility," said Dr Chavarro.

Further analysis of the findings showed that an extra serving per day of a low-fat dairy food such as yoghurt, appeared to increase the risk of anovulatory infertility by 11%, if the total daily intake of calories was unchanged. In contrast, an extra daily serving of a high-fat dairy food such as whole fat milk was associated with a 22% lower risk (with an unchanged calorie intake).

The study showed that the more ice cream the women ate, the lower was their risk, so that a woman eating ice cream two or more times a week had a 38% lower risk compared to a woman who consumed ice cream less than once a week.

Previous studies had suggested that lactose (a sugar found in milk) might be associated with anovulatory infertility, but Dr Chavarro's study found neither a positive nor negative association for this, and nor was there any association between intake of calcium, phosphorus or vitamin D and anovulatory infertility.