Today my friend and colleague, Lily Nichols, a fellow registered dietitian and certified diabetes educator, shares her insight on carbohydrate-restricted diets during pregnancy. This is a controversial topic that I believe deserves more attention and investigation, which Lily does brilliantly in the following article.
Is It Safe to Go Low Carb During Pregnancy?
With the wide adoption of low-carbohydrate diets, many people question if they are safe during pregnancy. While quite a few women use a lower carbohydrate diet to conceive (since they are especially useful for women struggling with infertility), most medical professionals discourage women from continuing this diet during pregnancy. I find it ironic that if you tell your doctor that you plan to eat low carb during pregnancy, they’ll say it’s unsafe, but if you say you plan to eat a diet based on fresh vegetables, meat, fish, eggs, dairy, nuts, seeds, and a little fruit, they’ll encourage you to stay the course. The controversy over the safety of low carbohydrate diets in pregnancy stems primarily from misconceptions around ketosis. It’s incorrect, but widely accepted, that ketosis during pregnancy is harmful to a developing baby.
When I first dove into the research, I was shocked to find that studies on healthy, non-diabetic pregnant women (eating a “regular” diet) show a marked elevation in ketones after a 12-18 hour fast, which is akin to eating dinner at 8pm and having breakfast at 8am (or skipping breakfast entirely). What’s more interesting is that pregnancy actually seems to favor a state of ketosis. Compared to non-pregnant women, blood ketone concentrations are about 3-fold higher in healthy pregnant women after an overnight fast. And in late pregnancy, metabolism shifts to a state of catabolism, making ketosis even more frequent. Knowing this, I would expect that every pregnant woman experiences ketosis at some point during her pregnancy (particularly if she experiences nausea or food aversions!).
I find it hard to believe that our bodies would perpetuate a state of ketosis if it was truly harmful to a baby, but I continued my research into the topic. The majority of studies on ketosis are actually looking at diabetic ketoacidosis (DKA) or starvation ketosis, not nutritional ketosis (induced by eating a low amount of carbohydrates).
First, let me state that diabetic ketoacidosis is an extremely dangerous phenomenon, pregnant or not, that occurs in people with insulin dependent diabetes. This is classically due to skipping insulin shots, incorrectly dosing insulin, or taking inadequate insulin to cover unexpected elevations in blood sugar. Unlike nutritional ketosis or starvation ketosis, DKA is accompanied by unnaturally high levels of ketones from complete insulin deprivation and blood sugar levels at least three times higher than normal, which profoundly and dangerously alters the acid-base balance in the body. The blood sugar levels seen with DKA are themselves teratogenic (can cause birth defects), so this state should obviously be avoided by pregnant women. Some studies have suggested the metabolic effects of diabetic ketoacidosis may harm fetal brain development.
However, to assume that all ketosis is harmful to a developing baby is illogical. For example, nutritional ketosis (the type of low level ketosis sometimes experienced on a low carbohydrate diet) is accompanied by normal blood sugar levels, blood ketones at very low levels (in general, thirty-fold less than what’s seen in diabetic ketoacidosis), and normal acid-base balance in the blood. So if a woman eats a lower carbohydrate diet during pregnancy, she might experience ketosis from time to time, but it’s not anywhere close to ketone levels induced by DKA in a pregnant woman with uncontrolled diabetes. Even if a woman tests positive for urinary ketones, it’s highly unlikely her blood ketone levels will be elevated. Studies on pregnant women who test positive for urine ketones rarely have detectable levels in the blood.
Despite all the medical warnings about ketones “harming the fetus”, it turns out the fetal brain actually gets approximately 30% of its energy from ketones. In fact, ketones are used by the growing fetus to synthesize a variety of essential cerebral lipids, which perhaps helps explain why ketosis is more common in the third trimester. And get this: Ketones are so important for fetal development, that researchers believe the fetus manufactures its own ketones. Umbilical venous blood samples (fetal blood supply) indicate significantly higher ketone concentrations compared to maternal levels in healthy pregnant women in their second and third trimesters.
So although the fetus requires glucose for growth, it also requires ketones. Either fuel provided in excess is harmful to the developing fetus, but as long as a mom is consuming enough calories and maintaining normal blood sugar levels, the baby will get just the right mix.
Given all of this information, I’ve changed my stance on the recommended carbohydrate levels for pregnant women and believe that it is safe to go low carb during pregnancy - at least lower than the arbitrary “minimum” of 175g per day suggested by most dietitians.
Now before you cut out all carbs, know that there are a variety of carbohydrate foods that pregnant women should continue to eat, including vegetables, fruit, nuts, seeds, and if they are tolerated, dairy and legumes. Eating fewer carbohydrates generally means women will eat less refined grains, junk foods, and added sugars, leaving more room for nutrient-dense foods that provide a growing baby with essential nutrients.
Many women do just fine eating a more moderate level of carbohydrates in pregnancy, so I do not believe everyone needs to goes low carb. But if you have medical conditions that are tied to blood sugar issues, such as gestational diabetes, preeclampsia, or you simply want to prevent excess weight gain, you should know it’s safe to eat a lower carbohydrate diet while pregnant.
*This article includes excerpts from Lily’s book, Real Food for Gestational Diabetes: An Effective Alternative to the Conventional Nutrition Approach, which includes an entire chapter exploring the research on ketosis during pregnancy.
Lily Nichols, RDN, CDE, CLT is one of the country’s most sought after ‘real food for pregnancy’ experts whose approach to nutrition embraces real food, integrative medicine, and mindful eating. You can learn more about Lily by visiting her popular blog, www.PilatesNutritionist.com and get her book, Real Food for Gestational Diabetes (and snag an exclusive FREE guide on managing gestational diabetes) at www.realfoodforGD.com.
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Franziska Spritzler, RD, CDE