Do Low-Carb Diets during Pregnancy Increase the Risk of Birth Defects?

I’m constantly inundated with concerns over the latest media headlines. Last month, a study titled “Low carbohydrate diets may increase risk of neural tube defects” was published in the journal Birth Defects Research (1). Media sources picked up the story:

Women with low carbohydrate intake are 30 percent more likely to have babies with neural tube defects, when compared with women who do not restrict their carbohydrate intake (2).

While this is true, it’s an oversimplification of the authors’ findings. In this article, I’ll break down the study design and give my interpretation of the dataset. I’ll also discuss other studies that may give us clues as to how many carbohydrates women need during pregnancy and how macronutrient intake during pregnancy may program our children’s metabolism for life.

Not only is nutrition during pregnancy important for supporting growth and development, it also programs the metabolism of our children for the world they will be born into. 

Breaking down the Study Results

In the study mentioned above, the researchers analyzed data from the National Birth Defects Prevention Study for infants conceived between 1998 and 2011. This included:

• 1,740 mothers of infants, stillbirths, and terminations with cases of anencephaly, where part of the brain or skull is missing, or spina bifida, where the spinal cord does not completely close
• 9,545 mothers of control infants born without birth defects

Not so fast, though. Here are my four qualms with this study:

• This 30 percent change is a change in relative risk. The absolute risk of giving birth to an infant with a neural tube defect is about one in 1,700 births, so any change to the absolute risk is still quite small.
• Carbohydrate intake prior to conception was estimated from food frequency questionnaires. Self-reported food intake is notoriously inaccurate and a huge problem in nutrition research. On average, the researchers interviewed women up to nine months after their due date and asked them to recall their diet in the year before pregnancy! Quick, can you remember how many carbs you ate a year and a half ago? I think you see my point.
• It was the folate intake that mattered most. As the authors report: “Our measures of carbohydrates and folic acid are not independent in that they both come from the same reported food.” Estimated dietary intake of folate among women restricting carb intake was less than half that of other women. Insufficient folate is well known to cause neural tube defects, so it’s much more plausible that this was the true cause for the difference.
• The effect also depended on pregnancy intention. The embryologic period of neural tube development often occurs before a woman realizes that she is pregnant. The author’s comment:

The association between restricted carbohydrate intake and NTDs was observed only among women with unintended pregnancies. We speculate this could be because women who intended to get pregnant made positive changes to their diet or began consistently taking the recommended dose of folic acid supplement.

This further suggests that folate deficiency is the culprit, not the low carbohydrate intake.

A more descriptive title of this study might be: “Low self-reported folate intake before conception is associated with an increased risk of neural tube defects. Women who have unplanned pregnancies while restricting carbohydrates may be most at risk for folate deficiency.”

But that’s not as catchy, is it?

What We Know from Traditional Cultures

Clearly, the study discussed in the previous section itself is not reason to avoid low-carbohydrate diets during pregnancy, provided that you mind your folate intake by consuming foods like liver and dark leafy greens. But are there other reasons to avoid a low-carbohydrate diet during pregnancy? Will it reduce the health of the child, whether at birth or later in life? These are the questions that I will try to answer in the remainder of this article. First, we’ll look at the role of carbohydrate in maternal health and practices of traditional cultures around pregnancy.

According to Weston A. Price, who journeyed around the globe to document the diets and lives of traditional cultures, special dietary practices were common around the time of conception, pregnancy, and lactation. In Africa and South America, people went to extensive lengths to properly prepare grains during this time:

Among many of the tribes in Africa there were not only special nutritional programs for the women before pregnancy, but also during the gestation period, and again during the nursing period. As an illustration of the remarkable wisdom of these primitive tribes, I found them using for the nursing period two cereals with unusual properties. One was a red millet which was not only high in carotin [carotene] but had a calcium content of five to ten times that of most other cereals. They used also for nursing mothers in several tribes in Africa, a cereal called by them linga-linga. This proved to be the same cereal under the name of quinua that the Indians of Peru use liberally, particularly the nursing mothers. The botanical name is quinoa. This cereal has the remarkable property of being not only rich in minerals, but a powerful stimulant to the flow of milk (3).

Carbohydrate is particularly important for supporting thyroid function, since insulin stimulates the conversion of inactive T4 to active T3. Cultures that subsisted largely on protein and fat for much of the year and had little access to plant foods had to make other arrangements to support fertility:

Among the Indians in the moose country near the Arctic Circle a larger percentage of the children were born in June than in any other month. This was accomplished, I was told, by both parents eating liberally of the thyroid glands of the male moose as they came down from the high mountain areas for the mating season, at which time the large protuberances carrying the thyroids under the throat were greatly enlarged (3).

In other words, these cultures could conceive healthy children without eating carbohydrate, but their fertility was not optimal unless they self-medicated with the thyroid glands of other animals.

The Fetal Origins of Disease

This is more formally called the “fetal origins of disease” hypothesis, which has been well supported by the scientific literature. The most oft-cited example is children who were born to women during the Dutch Hunger Winter during World War II. Severe undernutrition of these women early in pregnancy produced children who were metabolically programmed for a world where food was scarce and where conserving energy and storing fat was advantageous. When the famine ended and food became plentiful again, these children were predisposed to obesity and metabolic syndrome in adulthood (4).

Bringing it back to carbohydrate intake, it’s clear that we have two distinct questions:

• Does a low-carb diet during pregnancy prevent a woman from giving birth to a healthy baby?
• Does a low-carb diet pregnancy predispose offspring to disease later in life?

I think the answer to question #1 is clear. Most women can give birth to a healthy baby while on a low-carbohydrate diet, provided that they are obtaining adequate folate and other micronutrients (and that their thyroid health doesn’t suffer). Anecdotally, several women in the blogosphere report eating a low-carbohydrate or even ketogenic diet throughout pregnancy and lactation without issues.

However, the answer to question #2 is still a bit uncertain. There are only a few studies that have looked at carbohydrate restriction and how this affects the health of offspring later in life, but in general, they don’t favor low-carb diets.

• One study in humans found that the offspring of mothers who had consumed higher levels of protein and fat (likely resulting in lower carbohydrate intake) had significantly reduced insulin production in response to a glucose challenge 40 years later. For mothers consuming adequate protein, there was also an average 9.3 mm Hg increase in adult blood pressure for each 100 gram decrease in maternal carbohydrate intake (5).
• A similar study found that a high-protein, low-carbohydrate diet during pregnancy was associated with increased cortisol levels in the offspring 30 years later (6). (Unfortunately, these studies did not report micronutrient intakes.)
• Animal studies have suggested that a ketogenic diet during pregnancy may reduce the size of brain regions like the hippocampus in offspring, while increasing the size of others, such as the hypothalamus (7).

If the child sticks to a low-carb diet, she may be perfectly healthy. However, I think our goal as parents should be to maximize the metabolic flexibility of our children—particularly in a world full of readily available carbohydrates—such that they can remain healthy without unnecessary restriction.

Conclusion

To sum up, low-carbohydrate diets are not acutely harmful to the growth of the fetus, provided that micronutrient needs are met and the mother is not attempting to lose weight. However, wisdom from traditional cultures points to an increased need for carbohydrates during pregnancy, and carbohydrate restriction may have long-term implications on metabolic health and the ability to consume a wide variety of foods. Therefore, I think it’s safest to consume a moderate to high carbohydrate intake (about 75 to 150 grams) when pregnant or breastfeeding, unless a low-carb diet is being used therapeutically to treat a particular condition, such as gestational diabetes.

Of course, this does not mean bingeing on cakes, bread, and sweets. Simple sugars and refined carbohydrates have been associated with poor birth outcomes and increase the risk of gestational diabetes (8). Focus on high-quality carbohydrates like sweet potatoes, potatoes, plantains, fruit, and other starchy carbohydrates. These are packed with nutrients and fiber and accompanied by high-quality fats and proteins, will help to support the health of the mom and proper growth and development of the baby.

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