How Diet Affects Fertility

Every new life starts with two seemingly simple events. First, an active sperm burrows into a perfectly mature egg. Then the resulting fertilized egg nestles into the specially prepared lining of the uterus and begins to grow. The key phrase in that description is "seemingly simple." Dozens of steps influenced by a cascade of carefully timed hormones are needed to make and mature eggs and sperm. Their union is both a mad dash and a complex dance, choreographed by hormones, physiology and environmental cues.

A constellation of other factors can come into play. Many couples delay having a baby until they are financially ready or have established themselves in their professions. Waiting, though, decreases the odds of conceiving and increases the chances of having a miscarriage. Fewer than 10 percent of women in their early 20s have issues with infertility, compared with nearly 30 percent of those in their early 40s. Sexually transmitted diseases such as chlamydia and gonorrhea, which are on the upswing, can cause or contribute to infertility. The linked epidemics of obesity and diabetes sweeping the country have reproductive repercussions. Environmental contaminants known as endocrine disruptors, such as some pesticides and emissions from burning plastics, appear to affect fertility in women and men. Stress and anxiety, both in general and about fertility, can also interfere with getting pregnant. Add all these to the complexity of conception and it's no wonder that infertility is a common problem, besetting an estimated 6 million American couples.

It's almost become a cliché that diet, exercise and lifestyle choices affect how long you'll live, the health of your heart, the odds you'll develop cancer and a host of other health-related issues. Is fertility on this list? The answer to that question has long been a qualified "maybe," based on old wives' tales, conventional wisdom—and almost no science. Farmers, ranchers and animal scientists know more about how nutrition affects fertility in cows, pigs and other commercially important animals than fertility experts know about how it affects reproduction in humans. There are small hints scattered across medical journals, but few systematic studies of this crucial connection in people.

We set out to change this critical information gap with the help of more than 18,000 women taking part in the Nurses' Health Study, a long-term research project looking at the effects of diet and other factors on the development of chronic conditions such as heart disease, cancer and other diseases. Each of these women said she was trying to have a baby. Over eight years of follow-up, most of them did. About one in six women, though, had some trouble getting pregnant, including hundreds who experienced ovulatory infertility—a problem related to the maturation or release of a mature egg each month. When we compared their diets, exercise habits and other lifestyle choices with those of women who readily got pregnant, several key differences emerged. We have translated these differences into fertility-boosting strategies.

At least for now, these recommendations are aimed at preventing and reversing ovulatory infertility, which accounts for one quarter or more of all cases of infertility. They won't work for infertility due to physical impediments like blocked fallopian tubes. They may work for other types of infertility, but we don't yet have enough data to explore connections between nutrition and infertility due to other causes. And since the Nurses' Health Study doesn't include information on the participants' partners, we weren't able to explore how nutrition affects male infertility. From what we have gleaned from the limited research in this area, some of our strategies might improve fertility in men, too. The plan described in The Fertility Diet doesn't guarantee a pregnancy any more than do in vitro fertilization or other forms of assisted reproduction. But it's virtually free, available to everyone, has no side effects, sets the stage for a healthy pregnancy, and forms the foundation of a healthy eating strategy for motherhood and beyond. That's a winning combination no matter how you look at it.

Slow Carbs, Not No Carbs
Once upon a time, and not that long ago, carbohydrates were the go-to gang for taste, comfort, convenience and energy. Bread, pasta, rice, potatoes—these were the highly recommended, base-of-the-food-pyramid foods that supplied us with half or more of our calories. Then in rumbled the Atkins and South Beach diets. In a scene out of George Orwell's "1984," good became bad almost overnight as the two weight-loss juggernauts turned carbohydrates into dietary demons, vilifying them as the source of big bellies and jiggling thighs. Following the no-carb gospel, millions of Americans spurned carbohydrates in hopes of shedding pounds. Then, like all diet fads great and small, the no-carb craze lost its luster and faded from prominence.

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