The popularity of low-carbohydrate regimes like the Atkins diet could trigger a sharp resurgence in devastating birth defects and childhood cancers, scientists warn.
Bread, pasta, breakfast cereals and orange juice - which are largely shunned in low-carb regimes - are key sources of folic acid, a micronutrient essential to the neurological development of fetuses.
Since 1998, all white flour, white pasta and cornmeal in Canada have been fortified with folic acid.
As a result, the number of children born with neural tube defects has fallen by half. The incidence of neuroblastoma, a common childhood cancer, is down 60 per cent.
"Fortification is one of the greatest success stories in the history of medicine but, with so many people on low-carb diets, there is a real danger that those gains will be lost," said Gideon Koren, director of the Motherisk program at the Toronto Hospital for Sick Children.
Folate, or vitamin B-9, is found in leafy green vegetables like spinach, fruits like oranges, and in legumes like lentils and kidney beans.
The synthetic version, folic acid, is found in commercially prepared baked goods and pasta and can be purchased in supplements.
The recommended daily dose is four micrograms. A woman would have to eat about eight slices of white bread daily to reach that minimal level. Because almost half of all pregnancies are unplanned, supplements are recommended for all women of childbearing age.
Dr. Koren said in an interview that while he applauds efforts by people to maintain a healthy weight, women should avoid fad diets during their reproductive years because they will miss out on essential micronutrients, including folic acid, vitamin D and vitamin A.
"Low-carb diets are a striking example of how you can do something really bad for your child's health while trying to do good for your own health," he said.
Dr. Koren and a number of other scientists are planning to ask Health Canada to issue a formal warning to women about the risks of low-carb diets.
A recent survey revealed that one in every nine adults in North America is currently on a low-carbohydrate regime like the Atkins or South Beach diets and that twice as many again are planning to go that route in the next two years.
If they follow through with the diet plans, that would mean that as many as 75 million adults could be on low-carb diets in the United States and Canada by 2006.
The survey revealed that almost 40 per cent of people on low-carb diets had stopped drinking orange juice. An even larger number are likely to have abandoned bread. Canadian flour sales dropped almost 10 per cent in the last year.
The numbers have caught the eye of health groups and scientists.
"We're really beginning to worry about the popularity of low-carb diets but, at this point, we just don't know what the impact is going to be," said Nancy Green, medical director at the March of Dimes, a charitable group that works to prevent birth defects.
She said folic acid fortification has had such a dramatic impact that it follows that if people shun foods that are fortified, rates of birth defects could jump again.
The problem could largely be avoided if all women of childbearing age took a daily multivitamin that contains folic acid, she added.
Fewer than 300 children with neural tube defects are now born annually in Canada, down from more than 800 a year 15 years ago.