Q. How does an improved diet impact fertility?

A. According to Chavarro, most of the dietary factors that improve fertility impact "the body's ability to respond to insulin, which in turn improves ovulatory function, either by reducing the amount of glucose in the bloodstream after a meal (e.g., favoring low-glycemic carbs), by improving the ability of muscles to respond to insulin (e.g., increasing physical activity) or even by affecting the expression levels of genes known to affect insulin sensitivity (e.g., avoiding trans-fats)."

Folic acid and iron are "both very important in DNA replication and in the maturation of the egg prior to ovulation, and folic acid may improve the response of the ovary to follicle-stimulating hormone," added Chavarro.

Eating high-quality protein also appears to be important, according to Dr. Pak H. Chung, of Cornell University, primarily because gametes are essentially proteins.

Q. What should you NOT consume?

A. "Alcohol, because of its effects on folic acid; high-fat and trans-fat foods (because of effects on ovulation and long-term health); potentially toxic seafood (shark, tuna); raw dairy products (because of rare infectious diseases); and simple carbohydrates such as cakes and doughnuts (because they have no nutritional value and stimulate insulin)," said Chenette.

According to Dr. Eve Feinberg, a fertility expert in Illinois, caffeine has been associated with decreased uterine blood flow. "This, in turn, may prevent implantation of a developing embryo. Ideally, it is best to avoid caffeine in the pre-conception period."

Q. What about what the male eats?

A. "It is possible, with severe dietary indiscretion, to cause problems with sperm production, though this is unusual. There is data to indicate that antioxidants (glutathione and cryptoxanthin) are helpful for sperm production, but their effects are minimal," said Chenette.

The primary offender for male fertility is alcohol, he said. "The ability of this nonnutritional carbohydrate to get into every cell in the body and interfere with folate metabolism, as well as the typical junk-food diet that accompanies its use, are negatives. It interferes with male erectile performance," said Chenette.

Q. If diet is so important, what about all those who become pregnant while they are eating poorly or are overweight?

A. "A young woman with healthy eggs can conceive and deliver a child in the face of a poor diet, since the egg has such resiliency. An older woman with marginal eggs must take advantage of every practical measure to optimize egg quality. In cases of a severely poor diet, it is certainly possible, even in an otherwise healthy woman, to induce miscarriage, preterm labor, birth defects and fetal demise," said Chenette.

Q. What about multivitamins?

A. Most over-the-counter multivitamins are fine. "The only thing I would make sure of is that it has at least 400mcg of folic acid and 40mg of iron," said Chavarro. Supplementation with docosahexaenoic acid, an essential fatty acid, may also be beneficial. "This is one area where it is important to note that more is not better. High doses of vitamins and minerals can be toxic," said Feinberg.

Q. How important is exercise?

A. It's vital. "The greatest improvement in fertility with exercise (high-impact aerobic activities) is for those patients who have ovulatory dysfunction," said Feinberg.

However, be cautious. "Excessive exercise can be associated with the hypothalamic type of anovulation (not ovulating). Runners, for instance, have a lower tendency to have regular ovulation. I tell patients who ovulate on a regular basis not to intensify their exercise routine if they desire fertility," added Chung.

Charles Stuart Platkin is a nutrition and public-health advocate, and author of "Breaking the FAT Pattern" (Plume, 2006). Sign up for the free Diet Detective newsletter at www.dietdetective.com.