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Hopeful news for some of the more than 6 million women in the United States who suffer from infertility: A recent large study found that unlike other factors that you cannot control—such as age and genetics—eating certain foods and avoiding others is something you can do yourself, without medical intervention.
For eight years, the Harvard study followed 17,544 married nurses without any history of infertility as they tried to become or became pregnant. The research found that by changing five or more aspects of their diet (and exercise) habits, women with irregular or absent ovulation, which is responsible for 18 to 30 percent of infertility cases, reduced their risk of infertility by 80 percent.
One of the study's authors is Walter Willett, M.D., a professor of nutrition and epidemiology at the Harvard School of Public Health whose research is clearly outlined in The Fertility Diet (McGraw-Hill; co-written with Jorge Chavarro, M.D.). Here, Willett answers important questions about which foods are most—and least—fertility-friendly.
Fit Pregnancy: How much does the modern American diet have to do with rising infertility rates?
Walter Willett, M.D.: Probably quite a bit. Americans' high consumption of sugary sodas and fruit drinks, starches, red meat and trans fats is a big factor. The sad reality is that even in our study of nurses, fewer than 5 percent of the women had an optimal diet.
FP: Why do you recommend eating complex, or "slow," carbohydrates to enhance fertility?
WW: Your body digests bad carbs (like cookies, cakes, no-fiber breakfast cereals, sugary drinks, chips, white bread and white rice) quickly, and turns them into blood sugar. To drive down the blood-sugar spike, the pancreas releases insulin into the bloodstream. Good carbs (those containing fiber, such as fruits, vegetables, beans and whole grains) are digested slowly and have a more gradual effect on blood sugar and insulin. Previous studies have found that high insulin levels appear to inhibit ovulation. In our study, women whose diets had the highest glycemic load (a measure of the amount of bad carbs eaten and how quickly they're turned into blood sugar) were 92 percent more likely to have ovulatory infertility than those whose diets had the lowest glycemic load.
FP: How do trans fats affect fertility?
WW: Trans fats (found primarily in foods such as commercial baked and snack foods, animal products, french fries and some margarines) increase insulin resistance. Insulin helps move glucose from the bloodstream to the cells; resistance means it's harder to move glucose into the cells. The pancreas keeps pumping out more insulin anyway, and the result is more insulin in your bloodstream. High insulin levels cause a lot of metabolic disturbances that affect ovulation. (In a previous study, Willett and Chavarro found that each 2 percent increase in consumption of trans fats—as opposed to the same increase from carbs—was associated with a 73 percent increased risk for ovulatory infertility.)
FP: What about caffeine and alcohol?
WW: We didn't see any relationship with moderate consumption and fertility. One to two drinks of alcohol or several cups of coffee or tea a day had little effect on ovulation problems.
FP: You recommend full-fat dairy products for women trying to conceive over nonfat or low-fat ones. This contradicts the standard recommendation. Why?
WW: This is the part we understand least. But we found that the more low-fat dairy products in a woman's diet, the more trouble she had getting pregnant. The more full-fat dairy products she ate, the less likely she was to have trouble. We know that full-fat dairy foods convey the female hormones estrogen and progesterone. Skimming the fat from dairy also removes these hormones, which are attached to fat. Left behind are androgens, or male hormones. When male hormones are unchecked by female hormones, ovulation is impaired. (Regarding the recent sensational headlines about ice cream: Its impact was seen at two half-cup servings a week; at that rate, a pint should last about two weeks. If you gain weight from eating more, the extra pounds will offset any fertility benefits you might get from full-fat dairy.)
FP: Why do you suggest that women consume more protein from plants?
WW: Plant protein (from beans, nuts, seeds and tofu) comes with healthy fats and is relatively low in calories and can be helpful for weight loss. We found that a body mass index (BMI) between 18.5 and 24 is best for fertility. (For a BMI calculator, go to fitpregnancy.com/BMI.)
FP: Can taking vitamins make a difference if you're trying to conceive?
WW: Women in the study who took daily multivitamins containing 400 micrograms of folic acid were 40 percent less likely to experience ovulatory infertility over the eight years than women who didn't.
FP: What is the single most important diet change for women who are trying to conceive?
WW: There isn't one. Nutrition is sort of like an orchestra: You need to have all factors in place for the best result. If you practice all of our recommendations, it could have a large impact on your fertility. (See "Diet Changes That Aid Ovulation.")