A diet rich in ice cream and other high-fat dairy foods may lower the risk of one type of infertility, a study suggests. But the findings should not be considered licence to overindulge at the dairy bar, doctors say.

Yet the study is bound to get attention, because it's from the well-known Nurses Health Study at the Harvard School of Public Health and was published Wednesday in the European journal Human Reproduction. 

'It's not that having high fat is protective. It's that being on a diet may be bad for reproduction."'—Fertility specialist Dr. Zev Rosenwaks's interpretation of study

Researchers found that women who ate two or more low-fat dairy products a day were nearly twice as likely to have trouble conceiving because of lack of ovulation than women who ate less than one serving of such foods a week.

Conversely, women who ate at least one fatty dairy food a day were 27 per cent less likely to have this problem.

Even the researchers said women should not make too much of these results, which are based on reports of what women said they ate over many years — not a rigorous, scientific experiment where specific dietary factors could be studied in isolation.

Binging won't help

"The idea is not to go crazy and start to have ice cream three times a day," said the lead author, Dr. Jorge Chavarro, a research fellow at Harvard. "But it is certainly possible to have a healthy diet with low saturated fat intake by having one serving of high-fat dairy a day."

Others urged caution.

"A good healthy dose of skepticism is good for people," especially when the results are so hard to swallow, said Dr. Patrick Remington, a University of Wisconsin-Madison epidemiologist.

After all, the Nurses Health Study also found that menopause hormones could ward off heart disease — something doctors believed until a more scientific study disproved it several years ago, he noted.

The new research doesn't apply to most cases of female infertility, as a lack of ovulation is to blame only one-third of the time.

The study also found no link between infertility and dairy foods in general, something that bothered another statistics expert, David Allison at the University of Alabama at Birmingham.

Instead, researchers only saw a link when they separated non-ovulating women who ate yogurt and other low-fat dairy products from those eating more high-fat varieties.

When they looked at specific foods — and this is where the numbers really get tricky — they found that women eating ice cream two or more times a week had a 38 per cent lower risk of infertility than women consuming ice cream less than once a week.

Researchers adjusted the results to reflect differences in weight, exercise levels and other factors, but many specialists said they suspect weight is still mostly responsible for the results.

Dieting may be the problem

Weight extremes — being too thin or too fat — raise the risk of any sort of infertility, said Dr. William Gibbons, who runs a fertility clinic in Baton Rouge, La., and is president of the Society for Assisted Reproductive Technology.

Other research shows that women eating lots of low-fat dairy also eat other low-fat foods and try to lose weight, said Dr. Zev Rosenwaks, director of Weill Cornell University and New York Presbyterian's fertility services.

His interpretation of the new study: "It's not that having high fat is protective. It's that being on a diet may be bad for reproduction."

The Harvard study, funded by the university and a long-running federal study, involved 18,555 women, ages 24 to 42, who became pregnant or tried to conceive from 1991-99. Among them, 3,430 reported infertility, including 2,165 who saw a doctor for it. Of those, 438 said an ovulation problem was to blame.

The women filled out questionnaires every two years on what they ate and how often. Those who ate more high-fat dairy foods were more likely to consume alcohol and to already have had a child, and less likely to exercise than those eating low-fat dairy products.

Researchers said they adjusted for these factors and still saw the link to ovulation-related infertility.

If women do eat more high-fat dairy foods to try to boost their odds of conceiving, it would be important to cut calories elsewhere to avoid gaining weight, doctors said. They also should switch back to low-fat dairy foods once the baby is born, to limit saturated fats.