Can a 'fertility diet' get you pregnant?

Can a 'fertility diet' get you pregnant?

Can changing your diet improve your chances of getting pregnant? "The Fertility Diet," a new book by some prominent Harvard Medical School researchers, suggests that it can — that among other things, eating ice cream and cutting back on meat may help raise your fertility.

The problem is that much of the research behind the book doesn't live up to its hype. "The Fertility Diet" isn't the first to promote nutritional changes as a way to increase the odds of pregnancy; an online search will turn up any number of titles like "The Infertility Diet," "Fertility Foods" and so on.

Essentially, their recommendations are alike: a heart-healthy diet with more fruit and vegetables, less meat and bad carbs, more healthy fats and few or no trans fats.

While the messages are similar, a big difference is that the newest book comes from Harvard. As a result, it's had an enviable amount of buzz. Newsweek even devoted its Dec. 10 cover to an excerpt.

The notion that something as simple as better eating might improve fertility is certain to raise the hopes of tens of thousands of couples. But unfortunately, the findings in this book don't apply to a vast majority of people with infertility problems. Instead, they are based on women with ovulatory infertility, a condition caused by irregular ovulation that affects fewer than a third of infertile women.

And while it's never a bad idea to improve your nutrition, there is no definitive evidence that many of the diet changes outlined in the book will increase a woman's odds of getting pregnant.

"It's marketing," said Dr. Jamie Grifo, a respected fertility researcher who is director of the New York University Fertility Center. "There's a limit to what conclusions you can draw from the way they conducted the study."

The findings on fertility in the Nurses' Health Study come from more than 18,000 women who were trying to get pregnant over an eight-year period. But while that sounds like a lot, only about 400 of the women were given diagnoses of infertility related to irregular ovulation. So many of the associations between nutrition and fertility outlined in the book are based on a relatively small number of women.

It's important to note that while the study showed strong associations between certain habits and fertility, it did not prove that the women's diet was what made the difference. Furthermore, it was the women themselves who reported their eating habits, and only every few years. Critics note that most people can't remember what they ate last night, let alone over the course of a few years.

Two recommendations in "The Fertility Diet" are backed by relatively solid science. For a woman with irregular ovulation, attaining a healthy weight and taking a multivitamin with folic acid can improve her odds of getting pregnant. Being overweight or underweight has been shown to suppress ovulation, because both conditions throw off a woman's natural hormone levels.

In a major study of vitamins and folic acid to reduce the incidence of neural-tube defects in babies, the researchers noted a trend they hadn't expected. The women taking the vitamins were not only more likely to conceive, but also more likely to have twins.

The heart-healthy diet recommendations behind "The Fertility Diet" might influence ovulation because they affect insulin levels. Insulin levels, in turn, can affect sex-hormone-binding globulin, which can affect the amount of free androgen in a woman's body. Too much can suppress ovulation.

Importantly, the nurses' study found associations between fertility and certain eating behaviors, but it didn't test whether adopting new eating habits would make a difference. Dr. Walter Willett, the Harvard nutrition researcher who is a co-author of the book, acknowledges the limits of the data, but adds that he believes it is "highly likely" that the diet will help some women, given what is known about dietary influence on other body functions like blood pressure.

"The underlying principles are compatible with good health and prevention of some of the complications of pregnancy," he said. "This is a good eating strategy anyway. It's going to be clearly a safer, more modest approach to fertility than just jumping right into heavy medication."

The weakest recommendation in "The Fertility Diet" is the notion that ice cream and whole-fat dairy products will increase fertility. Even the study authors note in the book that it would be an "overstatement" to say there are even "a handful" of studies on the subject.

To their credit, the book's authors acknowledge early on that the research has limitations and that their diet doesn't guarantee a pregnancy. Dr. Jorge Chavarro, the lead author, said it had been a challenge to balance the limitations of scientific research with the commercial demands of book publishing. Even the simple title of the book, he added, belies the complexity of the findings.

"I would describe it as an apparently fertility-enhancing dietary pattern, but that doesn't go with the flow of your reading," he said. "This is not a cure for infertility. We have been very careful in explaining what we think these dietary changes can do and what they cannot do ."