If I'm not mistaken (and I could be; I'm a cardiologist, not a _____ologist) spina bifida is one of a class of developmental problems called "neural tube defects" and can be prevented, or at least minimized, if mother-to-be gets enough folic acid; this could well be the connection to diet. People who are malnourished, or who take too much alcohol, or who eat fad diets, are more susceptible than the general population to folate deficiency, and pregnant women need enough for two, which is the reason folic acid is an obligatory component of pre-natal vitamins.

See http://www.spinabifida.org/genetics.htm, from Dr. Bill's site/citation above; start a couple of paragraphs down.

Later on in life folate can be important for preventing nutritional anemia, and it's also prescribed with the hope of bringing down a high "homocysteine" level, thereby (maybe) giving a modicum of protection against coronary artery disease.