The problem is that much of the research behind the book doesn't live up to its hype. 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 A. 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.