Jun 04, 2008
The Fertility Diet: Eat Right to Get Pregnant
By Deborah Kotz
Posted November 30, 2007
One in seven American couples grapples with infertility, often with no explainable medical cause. A new book, The Fertility Diet, may offer a low-tech, low-cost solution for some. It's based on research from the well-respected Harvard Nurses' Health Study suggesting that diet may play a role in women's efforts to conceive. The book identifies particular nutrients they should be getting, such as iron, or avoiding, such as trans fats, to improve their chances of getting pregnant. How much are the odds increased? The book doesn't say. That's because the 10-step plan was formulated from dietary habits collected from surveys—and not actually tested on infertile women. While no one knows whether this plan can truly help women get pregnant, it's based, for the most part, on good nutrition and smart health habits. Book coauthor Jorge Chavarro, an investigator on the Nurses' Health Study and research fellow at the Harvard School of Public Health, spoke with U.S. News to explain how the Fertility Diet works.
How do you know food actually affects ovulation?
We don't know for certain, but we think this is the case, based on our data. We looked at nearly 19,000 female nurses who were actively trying to get pregnant to see if there was any link between what they ate and whether they became pregnant. We found some very interesting statistical associations. Those who took multivitamins containing folic acid, for example, were more likely to become pregnant. So, too, were those who had a high intake of iron, but it had to come from fruits, vegetables, beans, or supplements, not red meat. Trans fats from doughnuts, margarine, and other processed foods seemed to have a particularly detrimental effect on fertility.
Any theory as to why diet would have an impact?
We think it has to do with the hormone insulin and the function of the ovaries. Women who have healthy insulin levels are more likely to ovulate normally; those who have insulin resistance or diabetes are more prone to irregular ovulation. What's more, several studies, including ours, have shown that women who exercise moderately, about 30 minutes every day, are less likely to experience ovulation-related infertility than those who don't, and we know that exercise improves insulin levels. In fact, moderate activity, as well as nutrition, is a key part of the Fertility Diet.
Avoiding trans fats, which may also disrupt this hormonal pathway, is key as well. We recommend eating as little as possible—less than 2 grams per day—or even banning them altogether. Replacing processed foods with whole grains, fruits, and vegetables appears to have a beneficial effect on insulin levels, which could also promote healthy ovulation.
What is the single most important thing a woman can do to improve her fertility odds?
After a fertility workup on both the woman and man to determine underlying medical problems like blocked fallopian tubes or a low sperm count, I'd say the most important thing would be to get to a healthy body weight. Women who have a body mass index of 20 to 24 [between 117 and 140 pounds for someone 5 feet, 4 inches tall] have the best chance of getting pregnant. Those at either extreme of the weight spectrum, underweight or overweight, are more likely to be infertile. But I don't want to imply that obese women should throw in the towel. Numerous studies have shown that they can frequently jump-start ovulation by losing a modest amount, about 5 to 10 percent, of their starting body weight. So, the fertility diet recommends splitting the difference and aiming for a 7½ percent weight loss, which is 15 pounds for a woman who currently weighs 200 pounds.
Can having a small bowl of full-fat ice cream really help trigger ovulation, as the book jacket claims?
The Nurses' Health Study found that a daily serving of a full-fat dairy food, such as whole milk, ice cream, or cheddar cheese, increased a woman's pregnancy odds. This doesn't mean women can consume a nightly carton of Ben & Jerry's without guilt. The impact of ice cream was seen at two half-cup servings a week, which means a pint should last you two weeks. I'd rather see women replacing a low-fat yogurt with a full-fat one or adding whole milk to their cereal instead of skim. But I'm still skeptical about the full-fat dairy connection that we found in our study since high-fat dairy foods have been connected to poor insulin levels in other research. I consider it an optional part of the diet. Women can try a small amount, but they certainly shouldn't go overboard.