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Do Low-Carb Diets Cause Birth Defects?


A 2018 study suggests that a low-carbohydrate diet during pregnancy may increase the risk of neural tube defects by up to 30 percent.

The research triggered media headlines like, “Low carb diets like Atkins, Paleo or Keto linked to risk of birth defects including spina bifida, study claims.”

But do these sensational headlines tell the full story?

Read on to learn about the 2018 study and why it has some severe flaws, how to prevent birth defects if you follow the keto diet, and the potential benefits of low-carb diets during pregnancy.

The 2018 UNC Study in a Nutshell

In a new study published in January 2018, Dr. Tania Desrosiers, a Ph.D. epidemiologist, and her colleagues at the University of North Carolina Chapel Hill set out to understand the effects of carb restriction during pregnancy[*].

Specifically, they were concerned about folic acid deficiency.

Processed foods fortified with folic acid are known to decrease the rate of neural tube defects like anencephaly and spina bifida[*]. Therefore, the researchers suspected women who intentionally avoid refined carbohydrates during pregnancy might have lower levels of folic acid and a higher rate of these birth defects.

How The Study Was Done

Researchers decided to analyze results from a data set of 1,740 mothers of infants born, stillborn, or terminated with neural tube defects and compare them to a control group of 9,545 mothers of live-born infants without birth defects.

The researchers also used questionnaire data to estimate folic acid intake and carbohydrate consumption among the pregnant mothers-to-be.

They found that in the 5% of women who ate the fewest carbs (approximately 95 grams of carbs per day), dietary folate intake was less than half compared to the rest of the women on average.

More importantly, the study also demonstrated that eating low-carb with a low folic acid intake increased the relative risk of neural tube defects by 30%.

In the United States, the prevalence of neural tube defects is 5.3 per 10,000 births or about one out of every 1,900 births[*]. In absolute terms, that means the risk of neural tube defects went from about 0.053% to 0.069%.

In other words, the 30% greater relative risk shown in the study translates to an absolute risk increase of around 0.016%.

Problems With The Study

While the study provides some useful insight — folic acid is essential during pregnancy, and women who are low-carb but don’t eat a nutritious diet are likely to be deficient — the “low-carb” and “birth defects” subsets were both fairly small.

Here are a couple of problems with the study and how to fix them:

Problem #1: Get a Larger Sample Size

The study found a higher concentration of low-carb dieters in the “birth defects” group than in the healthy birth group, but there were only 564 low-carb individuals in total, and 1,740 mothers whose infants had neural tube defects.

To generate more reliable results, a larger overall sample size providing bigger subsets of these groups would be helpful.

Problem #2: Self-Reported Dietary Data

There are also several issues with the dietary questionnaire. Scientists already know dietary surveys aren’t very reliable; people aren’t very good at remembering what they eat, let alone reporting it on a questionnaire[*].

Problem #3: The Diet Questionnaire

Also — the food data reflected the year prior to pregnancy. While the UNC researchers argue that the diet during pregnancy tends to reflect the diet before pregnancy, it definitely introduces more uncertainty into the study.

Another problem is that the dietary folate intake and low-carb consumption are both estimated from the same questionnaire data. As a result, here’s what the researchers stated:

“We cannot assume, for example, that all women classified in our study as having restricted carbohydrate intake actually consumed fewer than 95 g/day

Of course, this doesn’t negate the study’s findings entirely, but it would be much better to have precise dietary information from the participants.

Problem #4: Participants Weren’t Low-Carb

Finally, as you probably realize, 95 grams of carbs may be low for the general population, but it’s not what most knowledgeable people would call low-carb. A better definition is fewer than 50 grams of carbs per day, or for keto, 30 grams or fewer of carbs daily.

But The Biggest Flaw Is…

It’s not very surprising that a folic acid deficiency from a nutrient-poor, low-carb diet results in birth defects. Most people are aware of the importance of folic acid during pregnancy.

But one shocking aspect of this study is that the researchers only found a correlation between a low-carb diet and neural tube defects in unintended pregnancies.

Here’s what they said:

“In our data, 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”

That’s what you might call a bombshell, but the full-text study only mentions it once. It’s nowhere to be seen in the abstract, and the press release and news stories don’t cover it, either.

And worst of all, there’s no control data to establish how common neural tube defects are in unintended pregnancies in women who aren’t low-carb, or how common they are in planned versus unplanned pregnancies.

It’s almost like the authors of the paper buried this vital information deep in the full text, behind a paywall, to get more attention and recognition for their findings.

“Low-carb diets may cause birth defects” sounds a lot more exciting than “low-carb diets may cause birth defects, but only in unplanned pregnancies.”

Are you ready for the punchline? In low-carb women who planned their pregnancies, there was a 13% reduction in neural tube defects.

That’s right: if you intend to get pregnant, according to the results of this study, your child is 13% less likely to have a neural tube defect if you eat a low-carb diet.

What is Folic Acid?

If nothing else, the 2018 UNC study is a reminder that folic acid is crucial during pregnancy.

Folic acid is one form of folate, a B vitamin. You can get it through food, oral supplementation, or injection.

Humans can’t make folate, but it’s required for cell division, amino acid metabolism, and the production of DNA and RNA. Folate deficiency can cause anemia, fatigue, heart palpitations, and tongue sores.

During pregnancy, the CDC and other US government agencies recommend women consume 400 micrograms of folic acid daily to prevent neural tube defects[*].

About 20-40% of women have insufficient or deficient levels of folic acid already (without being on low-carb diets), so it pays to get enough folate, whether or not you are pregnant currently[*].

Low-Carb Folic Acid Sources

If you eat keto or another low-carb, high-fat diet, then typically you avoid fortified refined carbohydrates with added folate.

While the easiest way to get enough folic acid is through supplements, it’s still possible to obtain adequate folate with a high-quality diet, including plenty of healthy fats and leafy greens.

Here are the top low-carb folic acid sources[*]:

  • 3 ounces of cooked beef liver has 215 mcg folate
  • One avocado gives you 160 mcg folate
  • A half-cup of cooked spinach contains 131 mcg folate
  • Four spears of boiled asparagus offer 89 mcg folate
  • A cup of shredded romaine lettuce has 64 mcg folate

As long as you eat plenty of healthy whole foods, you probably aren’t deficient in folic acid.

But if you are pregnant or plan to become pregnant, a high-quality folic acid supplement is an excellent idea to be on the safe side and ensure you get 400 micrograms each day.

Always talk to your doctor about supplementation if you’re pregnant or planning on becoming pregnant.

Should I Be Concerned About Birth Defects on a Low-Carb Diet?

No. You shouldn’t be overly concerned about neural tube defects or other birth defects if you’re low-carb, because you can use folic acid supplements or consume low-carb whole foods that offer dietary folate.

Although the 2018 UNC study conducted by Dr. Desrosiers and her colleagues caused a stir in the press, the results were not groundbreaking.

The researchers found that exclusively in unplanned pregnancies, the absolute risk of neural tube defects went from about 0.053% to 0.069% (a 30% increase in relative risk) when women consumed fewer than 95 grams of carbs per day.

What wasn’t mentioned in the study summary, press release, or media coverage was this: low-carb moms-to-be who planned their pregnancy were 13% less likely to give birth to babies with neural tube defects.

This is likely because these women started taking a prenatal or otherwise began consuming more folate once they realized they were pregnant.

It’s a question of folic acid levels, not carbohydrate intake.

While neural tube birth defects are a tragic issue that no one deserves to experience, they’re related to unplanned pregnancies and poor dietary habits, not low-carb diets per se.

Are There Benefits to Low-Carb, High-Fat Diets During Pregnancy?

Not only are low-carb diets like the keto diet safe during pregnancy (as long as you avoid fasting and eat adequate amounts of nutritious foods), they also happen to offer some significant benefits:

  • Research suggests low-carb diets may prevent gestational diabetes[*]
  • Children of mothers who maintain a healthy weight are less likely to be overweight or obese[*]
  • Mothers who eat a healthy diet may pass on a healthier microbiome to their babies[*][*][*]
  • Healthy fats are essential for fetal brain and central nervous system development[*][*]

Low-carb, high-fat diets aren’t required for a healthy pregnancy, but they’re a fantastic way to enhance your health and wellness and reduce your risk of disease and may do the same for your baby.

The Takeaway: Get More Folic Acid if You’re Pregnant

Most potential mothers care immensely about having a healthy pregnancy. As a result, clickbait headlines about diet and birth defects get a lot of shares and attention.

The media coverage of the 2018 UNC study linking low-carb diets to birth defects represents a cautionary tale. Unfortunately, you can’t necessarily trust most science news stories for accuracy or completeness.

Dietary intake of folic acid plays a much more significant role than carb intake when it comes to your child having a higher risk of neural tube defects like spina bifida or anencephaly.

If you eat a low-carb, high-fat diet like keto, the good news is that as long as you get the recommended 400 micrograms of folic acid each day through food or folic acid supplementation, you are probably less likely to have a baby with birth defects compared to women who eat conventional diets.

And as always, talk to your health care provider if you’re following a special diet while pregnant or breastfeeding.

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