Home remedies to boost the odds of becoming pregnant include thinking positive thoughts and placing a pink or blue ribbon under a bed pillow, depending on whether a mother-to-be is hoping for a girl or a boy.

But women who want to try something with a bit more science behind it can start by changing their eating habits. So say Harvard doctors who recently completed a study on women's diets and fertility.

Their findings suggest that certain foods and lifestyle factors can significantly affect hormone levels and improve fertility in women with ovulation problems - a common cause of infertility, says Dr. Jorge Chavarro, lead author of the study, which was published last month in the journal Obstetrics & Gynecology.

What he and his colleagues found supports a growing body of evidence that diet can greatly affect hormone levels, particularly insulin, which then affects fertility. Although the research does not prove that certain foods have a direct effect, it does suggest that a woman can increase the odds of becoming pregnant without risky, costly or invasive treatments - something many women, and their doctors, may overlook.

"Making changes to your lifestyle should be a first step when people are facing problems with fertility," says Chavarro, a research fellow at the Harvard School of Public Health's department of nutrition.

Lifestyle changes

In the study, women who followed five or more lifestyle or dietary recommendations (see box at left) reduced their risk of ovulatory infertility by as much as 80 percent compared with women who engaged in none of the recommendations.

Ovulation problems - in which women ovulate irregularly or not at all - account for 18 percent to 30 percent of all infertility cases, Chavarro says. Doctors often prescribe fertility drugs as treatment, but the medication can raise the risk of conceiving twins or higher-order multiples, which can lead to other complications.

The study should open some eyes in the field of reproductive medicine, says Dr. Fady Sharara, a Virginia fertility doctor who has studied fertility and body mass index and has long supported the value of a healthful diet for fertility.

"I'm so happy that this paper came out," says Sharara, medical director of the Virginia Center for Reproductive Medicine. "I've been telling my patients for years that you have to change your diet. I personally believe that this is very important for many women, not just those who are overweight."

A new take on infertility

Few studies have specifically examined diet and infertility. The recent findings were culled from the long-running Nurses' Health Study II, an epidemiology study of registered nurses launched at Brigham and Women's Hospital in 1989. For the fertility analysis, the researchers analyzed data collected from 17,544 women with no history of infertility over eight years as they tried to become pregnant or became pregnant. They surveyed the women on their diets, exercise habits, weight and many other health factors.

In general, the study's findings point to factors that can disrupt the delicate balance of hormones needed for reproduction. Although the researchers aren't sure why certain foods seem to influence fertility, they have some strong hunches based on other scientific studies, says Chavarro, who has written a book based on the findings, "The Fertility Diet," with Dr. Walter Willett of Harvard. Willett is a widely published researcher and one of the nation's leading nutrition epidemiologists.

Research has shown, for example, that women with a disorder called polycystic ovary syndrome frequently experience ovulatory infertility due to insulin sensitivity and high testosterone levels. They are more likely to get pregnant after they lose weight or are treated with medications to improve insulin sensitivity.

Interesting data

One recom-mendation in "The Fertility Diet," is for women to avoid refined carbohydrates such as white bread, potatoes and sugary sodas, which quickly raise blood sugar and insulin, disrupting the balance of hormones. In the Nurses' Health Study II, women who had the highest glycemic load - a measure of the amount of carbohydrates in the diet and how quickly carbohydrates are turned into blood sugar - were 92 percent more likely to have had ovulatory infertility than women in the lowest glycemic load category.

"There are a lot of papers in the literature on body mass index and its effects on fertility," says Dr. G. David Adamson, president of the American Society for Reproductive Medicine who was not involved in the study. "This study certainly adds some very interesting data."

Another strong correlation was found with the amount of trans fats women consumed. The study found that eating a modest amount of trans fat - just 2 percent of calories - in place of healthier fats and carbohydrates would raise the risk of infertility by 73 percent to 131 percent.

Some fats help

Monounsaturated fats, such as those found in olive oil and canola oil, on the other hand, help increase insulin sensitivity and improve fertility.

One of the more surprising findings of the study was that whole milk and ice cream appear to be among the most potent fertility foods. That discovery does not have an obvious explanation, Chavarro says. It could be that removing fat from milk alters its hormonal composition, deleting estrogen and progesterone and leaving an excess of male hormones that can affect ovulation.

In the study, the researchers found that one serving a day of a low- or nonfat dairy product increased the risk of ovulatory infertility by 11 percent. But adding one serving per day of a full-fat dairy product, particularly whole milk, decreased it by 22 percent.

"The Fertility Diet" recommendation is to get one or two servings a day of whole milk or other full-fat dairy foods. But, Chavarro cautions, don't go crazy with the Haagen-Dazs. The idea is to balance the ratio of male to female hormones - not pack on pounds, which in itself can disrupt the balance of hormones needed for reproduction.

"Having one glass of whole milk every day is different than having a gallon of whole milk and a bowl of ice cream," he says. "We know one of the best ways to improve insulin sensitivity is to lose weight. So weight control is among the top priorities of the diet" even while including some high-fat dairy in the diet.

Multivitamin, iron

Other recommendations include taking a multivitamin and iron. Although American women of childbearing age are advised to consume 400 micrograms of folic acid per day to prevent neural tube birth defects, the nurses study found that ovulation and conception improve with consumption of at least 700 micrograms per day.

The study also found that women who regularly took an iron supplement of at least 40 milligrams a day were 40 percent less likely to have trouble getting pregnant. But this was only true of women who got the iron from fruits, vegetables, beans and supplements.

Those who consumed iron from mostly meat, which contains a different form of iron than that found in other food sources, weren't protected from ovulatory infertility. Previous research suggests that a woman's eggs and the embryo need iron to function properly.

Overall, Chavarro says, the more of these dietary factors a woman adheres to, the greater her chance of improving ovulatory function. The diet has no effect on other causes of infertility, such as blocked fallopian tubes - or a low sperm count in men.

Plans are under way to conduct a randomized, controlled study to test the diet in a more scientifically rigorous manner, Chavarro says. In the meantime, achieving a healthy weight is a good first step for any woman planning a pregnancy, he says.

10 ways to enhance fertility

"The Fertility Diet," based on a Harvard study, offers 10 key recommendations to enhance fertility:

* Avoid trans fats.

n Use more unsaturated vegetable oils, such as olive or canola oil.

n Eat more vegetable protein, such as beans and nuts, and less animal protein.

n Choose whole-grain sources of carbohydrates instead of highly refined carbs.

n Drink a glass of whole milk or have a small dish of ice cream or full-fat yogurt each day.

n Take a multivitamin that contains folic acid and other B vitamins.

n Get plenty of iron, but not from red meat.

n Avoid sugary sodas. Coffee, tea and alcohol are OK in moderation.

n If overweight, lose 5 percent to 10 percent of your weight.

n Start an exercise program. If you already exercise, keep it up but don't overdo it if you are quite lean.

- Los Angeles Times