Will switching from low-fat milk to whole milk increase a woman’s chances of becoming pregnant? Maybe. It’s one of the recommendations in The Fertility Diet (McGraw Hill, 2009), a book by Jorge Chavarro, M.D., and Walter C. Willett, M.D.
The book, which has garnered a good deal of press since its release, offers dietary changes a woman can make to help her chances of conceiving. But it’s important to note that those changes won’t solve most infertility cases.
More than 6 million women – or one in seven couples – in America today struggle with infertility, a word they inherit after trying, unsuccessfully, to become pregnant for one year. (The number includes women who’ve had one child but face “secondary infertility” in trying to have another.) Approximately 30 percent of these women have issues caused by irregular ovulation, and it is this group the book studies and sets out to help. Dietary changes won’t boost the fertility of the 70 percent of infertile women who have anatomical problems, such as fibroid blockages in the fallopian tubes or other issues.
The book is based on part of the eight-year Nurses’ Health Study II – researchers asked 18,000 nurses who were trying to become pregnant to provide information on what they ate, their lifestyles, and personal and medical histories. Nurses were chosen for their training and skill in providing accurate information, and were asked to supply information every two years. (To learn more about this part of the study, visit nurseshealthstudy.org.)
What Chavarro and Willett found were some surprising connections. “Going into the study, we had no strong reason to believe there was a relationship between dairy and fertility,” says Chavarro, a research fellow who is studying the role of diet and lifestyle on reproductive function at the Harvard School of Public Health. “The benefit of high-fat was a big surprise.” He’s quick to point out that for everyone outside the fertility issue it’s best to stick to low-fat dairy for heart health.
The other surprise, Chavarro says, was the magnitude of the relationship between diet and infertility.
When it comes to irregular ovulation and infertility, diet matters, say Chavarro and Willett. And weight is also an important consideration. To women who suffer from ovulatory infertility, the book offers 10 basic recommendations:
1. Avoid trans fats, found in fast foods and many commercial products. Check package labels for amounts of trans fats and avoid anything that contains a “partially hydrogenated” ingredient.
2. Cut back on saturated fat from red meat and palm and coconut oils, and use unsaturated oils, such as olive and canola.
3. Eat less animal protein and more vegetable protein, such as beans and nuts.
4. Choose whole grains, which have lower, slower effects on blood sugar, over highly refined carbohydrates, which boost blood sugar and insulin production.
5. Temporarily trade skim or low-fat dairy products for their full-fat counterparts – one glass of whole milk or one serving of full-fat yogurt or ice cream daily.
6. Take a multivitamin that contains folic acid and other B vitamins.
7. Get plenty of iron from fruits, vegetables, beans and supplements, not from red meat.
8. Drink water; have coffee, tea and alcohol in moderation. Avoid sugared sodas.
9. If you are overweight, lose between 5 percent and 10 percent of your weight.
10. If you aren’t physically active, start a daily exercise plan; if you’re quite lean, don’t overdo exercise.
With the exception of full-fat dairy and vitamins containing folic acid, the above advice was the basis for Walter Willett’s earlier book, Eat, Drink and Be Healthy (Free Press, 2003), which stressed the importance of eating well and controlling weight for all men and women. Willett, who chairs the Department of Nutrition at the Harvard School of Public Health, outlined a diet to inspire readers to weigh what they did in their early 20s, give or take a few pounds.
Will it bring on pregnancy?
“Women who have issues with ovulatory fertility who follow five or more of these recommendations have a substantial chance of getting pregnant,” Chavarro says. “In two out of three cases, women can get pregnant by moderate changes to diet and lifestyle.”
Willett and Chavarro say weight is an important fertility factor for men, as well as women. New research indicates that overweight men have a lower sperm count than men of healthy weight.
As for women, while being too thin to sustain an ovulatory cycle is also a problem, more women are at risk for infertility because they are overweight. Body fat can contribute to insulin resistance and disrupt ovulation. While Willett and Chavarro recommend that overweight women lose 5 percent to 10 percent of their starting weight, to make that goal more reachable, their book suggests the 7.5 percent solution: “12 pounds for a women starting at 160 pounds, 15 pounds for one starting at 200 pounds, and 19 pounds for one starting at 250 pounds. Although such goals are a challenge, they are far less daunting than ‘aiming for a healthy weight,’ the advice usually offered by health-care professionals.”
Many women worry about the increased risk of infertility as they age. Citing American Society for Reproductive Medicine statistics, Willett and Chavarro write that fewer than 10 percent of women in their early 20s have issues with infertility, compared to nearly 30 percent of those in their early 40s, and 50 percent or more of those over age 45. Here again, dietary changes can help with infertility at a wide range of ages.
“In our study, the relation between diet and infertility did not differ by a woman’s age,” Chavarro says. “Women in their 20s were as likely to benefit from the diet as women in their 30s. And increases in body weight with age can add to the effects of age itself.”
But Chavarro has this caveat: “We know that fertility decreases with age, and there is a trend now toward later child bearing. Many women get the mistaken impression that they can delay the age they get pregnant and rely on fertility treatments later.”
The national Centers for Disease Control and Prevention (CDC) tracks the success rates for fertility clinics across the country. Most recently, the CDC reported that the rate of infertile couples finally able to have a baby is around 20 to 29 percent overall.
“Biologically, younger women have a better capacity to get pregnant,” Chavarro says. “But it’s a difficult issue. They have to consider their personal goals.”