For some women, all it takes is a month of “trying” to become pregnant. For others, conception may not happen for months, and sometimes years. In fact, 6.1 million American couples (or 10 percent of couples of childbearing age) have had trouble conceiving, according to the American Pregnancy Association.

What makes one couple fertile while another struggles to conceive? One obvious factor is age: More women in the United States are waiting longer to have kids. About 20 percent of women wait until after age 35 to start a family. Fertility naturally starts to decline with age; on average it takes one to two years for a couple over age 35 to conceive.

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To help the process along, some women undergo expensive drug-based and surgical fertility treatments, which work only 25 percent of the time. But recent research points to a handful of natural keys to fertility. A healthy diet and daily physical activity top this list. In fact, adopting five or more lifestyle choices—including weight control, physical activity, and proper diet—lowers the risk of ovulation-related infertility by 69 percent, according to the Harvard researchers who authored The Fertility Diet (McGraw-Hill, 2009). Why? Too much insulin, which is regulated by diet and exercise, overstimulates production of male hormones in the ovaries and blocks the liver’s production of sex hormone-binding globulin (SHBG). Less SHBG gives rise to more free testosterone circulating, and this excess testosterone can stop ovulation by disrupting development of the follicles that house eggs.

Here are experts’ beyond-the-basics suggestions for increasing your fertility. But be patient: “It could take a few months before there could be observable effects on fertility,” says Jorge Chavarro, MD, a coauthor of The Fertility Diet and a nutrition scientist at the Harvard School of Public Health.

Cut out trans fats

Weight gain isn’t the only problem with diving into bags of chips and cookies. Increasing trans fat intake by just 2 percent (about 4 grams per day) could increase a woman’s risk of infertility due to anovulation (when ovaries do not release an egg) by as much as 79 percent. Trans fats make it harder for the body to respond to insulin, and the body reacts by secreting more insulin (this is known as insulin resistance), Chavarro explains. Greater insulin levels influence the levels of other hormones, including many that directly affect ovulation. Focus on monounsaturated fats instead, such as those found in olive and other vegetable oils and foods like avocados, says Chavarro. Monounsaturated fats increase fertility by improving insulin sensitivity and reducing inflammation, he explains.

Tackle excess weight

Losing 5 percent to 10 percent of your body weight if you’re overweight, defined as a body mass index (BMI)score of 25 to 29.9, can help jump-start ovulation. A recent U.K. study, presented at the European Society for Human Reproduction and Embryology meeting in 2009, found that a 5 percent decrease in BMI—regardless of starting weight—resulted in a significant increase in blood flow to the womb, which can help trigger egg release from the ovaries and implantation. Weight loss boosts insulin sensitivity, which in turn improves levels of many reproductive hormones, Chavarro says. It also decreases levels of inflammatory markers, which can interfere with ovulation and implantation. On the other hand, being too thin also can disrupt ovulation. If you want to be in what the Harvard team calls “the fertility zone,” aim for a BMI of 20 to 24.

Choose slow carbs

Eating carbs that are lower on the glycemic scale—whole grains rather than processed ones—also helps control insulin levels, says Brandy Webb, ND, a resident at Bastyr Center for Natural Health in Seattle and director of Sage Natural Health and Fertility in Tacoma, Washington. “Overconsuming high-glycemic foods causes chronically elevated insulin levels,” she says. The resulting insulin resistance can interfere with fertility by leading to excess androgens (DHEA and testosterone) in females, which can cause anovulation. Choose from the American Diabetes Association’s list of the top ten low-glycemic, nutrient-rich foods: beans, dark leafy vegetables, citrus fruits, sweet potatoes, berries, tomatoes, omega-3-rich fatty fish, whole grains, nuts, and nonfat dairy. You also can lower a meal’s glycemic value by adding lean protein, monounsaturated fats, and fiber. So if you’re having pasta, for example, choose whole grain noodles and add nuts, chicken, or seafood.

Exercise, but not too much

A moderate 30 to 60 minutes daily boosts fertility, says Chavarro, by helping control insulin and weight, regulating the menstrual cycle, and reducing stress. “Exercise needs to be balanced with body weight. For women who are very lean, exercising could actually be counterproductive for their fertility,” he says. If your BMI is above 25, consistently aim for 60 minutes or more per day. Try to include aerobic exercise, strength training, stretching, and daily living activities such as housework.

Just relax

Hearing that trite advice can be frustrating, but scientific evidence consistently indicates that stress reduction definitely ups your odds of conceiving. For example, infertile women who participated in a ten-week mind-body workshop that included muscle relaxation, yoga, and imagery were nearly three times as likely to get pregnant within a year than those women who didn’t.

“There’s certainly a psychosocial component to getting pregnant,” suggests Dorothy Greenfeld, MSW, director of behavioral services at the Yale Fertility Center of Yale University. Moreover, she explains, anxiety and stress can upset a woman’s menstrual cycle by delaying or stopping ovulation. But what’s more important than how or why it works, says Greenfeld, is finding out what works for you.

“Women respond differently to stress than men, and than other women as well,” she says. “Sure, acupuncture, massage, and yoga may help. What really helps is trying to increase pleasurable activities. Reading trashy novels, walking, unscheduled sex … anything to temporarily take your mind off trying to get pregnant.”