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Health Sense

Book on fertility and diet stirs buzz, skepticism

Email|Print| Text size + By Judy Foreman
December 24, 2007

Researchers at the Harvard School of Public Health have created a buzz with their new - and controversial - book, "The Fertility Diet."

The book doesn't actually come right out and claim that the new Harvard diet is a cure for infertility. But that's the message desperate couples could be forgiven for getting, given its title, some of the authors' public statements, the intense media hype, and, of course, the clout of almost anything with the Harvard imprimatur. That's why some critics are upset.

The book, by epidemiologists Drs. Walter Willett and Jorge Chavarro and writer Patrick J. Skerrett, is based on the authors' research, published in the November issue of "Obstetrics and Gynecology."

In that paper, the authors reported on 17,544 women participating in the Nurses' Health Study who recorded their diets and their quests to get pregnant in biennial questionnaires.

The study found that women had a lower risk of infertility due to anovulation - the failure to produce a viable egg every month - if they ate a diet that emphasized monounsaturated fats like olive oil over trans fats often found in baked goods; vegetable proteins such as in beans and nuts rather than animal sources such as red meat; whole grains instead of refined carbohydrates that cause too rapid a rise of blood sugar and insulin; some whole milk, a little ice cream or other high-fat dairy products daily; multivitamins containing folic acid; and iron from plants and supplements.

The study is groundbreaking because it "is one of the first times that anyone has shown that what you eat and drink can impact the reproductive system," said Alice Domar, a psychologist who heads the Domar Center for Mind/Body Health at Boston IVF, one of the country's largest infertility centers.

But it's a huge leap to go from a statistical correlation to actually giving advice. The authors veer toward prescription when they say in their book, "We have discovered 10 simple changes that offer a powerful boost in fertility for women with ovulation-related infertility." Ditto, in a cover story they wrote for the Dec. 10 issue of Newsweek, when they said their recommendations are aimed at preventing and "reversing" infertility - a conclusion Willett defended in an interview.

Observational studies like the Nurses' Health Study do not prove that a behavior causes or prevents a health problem, only that it might do so. To prove that diet affects fertility, researchers would have to take a group of women with diagnosed infertility and randomly put half on a special diet and half on a regular diet and compare conception rates.

This would be an interventional study, which would have come closer to the "gold standard" of medical research and would have provided the solid ground to offer advice. Such a study could also show how long a woman would need to eat this way to affect her fertility.

Dr. Guy Ringler, a fertility specialist at California Fertility Partners and a board member of the American Fertility Association, cautioned in an e-mail that the new findings are interesting but "not sufficient to conclude that a modified diet in an infertile population would improve fertility. There need to be randomized, prospective studies comparing the different diets before such claims could be made."

So where's the harm in a little hype? Since the diet is basically a healthy one, except for the controversial suggestion to eat more high fat dairy, including ice cream, it is unlikely to cause direct harm. But a woman who follows the diet and still doesn't get pregnant may blame herself, even though the diet isn't proven effective.

Worse yet, a woman may follow the diet and postpone seeing a doctor. "If you're 22 and you follow this diet for six months, that's no big deal. But if you're 42, you can't afford to postpone seeing a doctor and try this diet in the meantime," said Domar.

Dr. Gil Wilshire, a reproductive endocrinologist at Boone Hospital Center in Columbia, Mo., put it even more strongly: "This book is blatantly irresponsible. I am going to be cleaning up the damage from this book for years to come. I will be having women who wasted one, two, three years of their lives with imprecise, ineffective treatment. Those are precious years you can't get back."

But the book has obvious market appeal. Infertility is a source of heartache for more than 6 million American couples, although infertility due to problems with ovulation only account for about one-quarter of these cases. The diet won't help if male biology - such as inadequate production of viable sperm - is the problem, as the authors themselves note. Or if the woman has blocked fallopian tubes or fibroids that impair the lining of the uterus.

All this said, the observations make biological sense, particularly the idea that certain foods may influence levels of hormones involved in ovulation and conception.

For instance, a diet high in refined carbohydrates is detrimental to ovulation because it sends blood sugar and insulin, the hormone that escorts sugar into cells, skyrocketing, Willett said in a telephone interview. Too much insulin makes the ovaries overproduce testosterone, the male hormone. Meanwhile, insulin reduces production by the liver of a protein called SHBG (sex hormone binding globulin), which captures testosterone. The net result of these processes is too much testosterone in the bloodstream, which can impede ovulation.

The ice cream recommendation is surprising, Willett acknowledged, and a bit tricky to explain. But his research suggested that "higher fat dairy products were related to better fertility and lower fat dairy was related to lower fertility. The reason? We're only speculating, but it may well be that the relatively modest amounts of estrogen and progesterone that are present in the fatty part of whole milk can have a positive effect on fertility," he said.

The Harvard team is not recommending a switch to high-fat dairy for a whole lifetime - if consumed long-term, high fat dairy products can increase the build-up of fatty plaques in artery walls, contributing to heart attacks.

The take-home message? If you're having trouble getting pregnant, see your doctor before you hit the bookstore.

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