From the World Health Organization's Report

Carmichael and her colleagues wondered if eating a healthy, balanced diet could have the same protective effect as getting extra vitamins and minerals through supplements. They used data from the National Birth Defects Prevention Study to compare about 3,400 women who had a baby with a neural tube defect or a cleft lip or palate, and 6,100 women whose babies didn't have a birth defect.

Each of those women completed a phone interview in the two years after her baby was born. Researchers asked the new mothers how frequently they had eaten a range of foods, from beans to candy, in the few months before they became pregnant. Then they calculated how closely women had followed the so-called "Mediterranean diet" ir the U.S. Department of Agriculture's Food Guide Pyramid.

After taking into account how much the women weighed, whether they took vitamins and if they smoked and drank, Carmichael and her colleagues found that those who more closely followed either healthy diet were less likely to have babies with any of the birth defects they studied.

In particular, women with a diet closely matching the USDA Food Guide Pyramid were half as likely to have a baby missing part of its brain and skull -- a birth defect called anencephaly -- than women whose diet was farthest from those guidelines. They were also 34 percent less likely to have a baby with cleft lip and 26 percent less likely to have one with cleft palate.

From the World Health Organization's Department of Nutrition of Health and Development in Geneva, cautioned that with the current evidence about the benefits of prenatal supplements, a good diet isn't enough. On a global scale, especially in places where diets aren't as good, folic acid is still a priority for preventing birth defects, she told Reuters Health. "If a woman is trying to get pregnant, a good diet should be a complement to the use of folic acid supplementation, not a substitute," said de Regil, who wasn't involved in the study.