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Having trouble getting pregnant? Maybe you are not eating enough ice cream, say researchers who found that a low-fat dairy diet can cause infertility, by preventing ovulation.
This type of infertility, known as anovulatory infertility, was far more common in women who ate low-fat dairy products such as skimmed milk and low-fat yoghurt, the study found.
Jorge Chavarro at Harvard School of Public Health in Boston, Massachusetts, US, and colleagues tracked more than 18,000 women aged between 24 and 42 with no history of infertility. Every two years over an eight-year period, the women were asked if they had tried to become pregnant, whether they had been trying for more than a year without success, and the medical reasons for any fertility problems. The women also supplied detailed information about what they consumed during this time.
Women who ate two or more servings of low-fat dairy foods a day increased their risk of ovulation-related infertility by 85% compared with those who ate less than one serving of low-fat dairy food a week. Conversely, women who ate at least one serving of high-fat dairy food a day, such as ice cream or full-fat milk, reduced their risk of anovulatory infertility by more than 25% compared with women who consumed up to one serving a week.
Women trying to conceive should adjust their diet, if only temporarily, Chavarro says. â€œThey should consider changing low-fat dairy foods for high-fat dairy foods,â€ he says, noting that the rest of the diet could be adjusted to achieve the same overall calorific intake. â€œOnce you are pregnant, you can always switch back.â€
Chavarro does not know why dairy fat affects fertility in this way. Other types of fat that he and others have studied do not have the same effect. â€œItâ€™s either something specific to dairy fat, or a fat-soluble substance present in dairy foods that reduces the risks of infertility,â€ Chavarro says.
Processing whole milk into low-fat milk may not only strip away the fertility benefits of dairy fat, but may also raise levels of hormones that interfere with female sex organs. To turn whole-fat milk into skimmed milk, whey protein is often added back for taste and colouring. The protein has been found to produce testosterone-like effects in mice, Chavarro says.
It may simply be the over-processing of low-fat foods that is causing increased infertility, says Nanette Santoro, director of the reproductive endocrinology division at the Albert Einstein College of Medicine in the Bronx, New York, US.
But Santoro adds that the most important factor of all may be maintaining a healthy body weight. There is a clear relationship between increasing weight and infertility, she says, pointing out that women with very low body fat risk infertility. One of the best self-help things women can do is maintaining an optimal body weight neither too thin nor too large.
Journal reference: Human Reproduction doi:10.1093/humrep/dem019