Experts debate benefits of low-carb diets for gestational diabetes

Key takeaways:

• Low-carb diets may decrease glycemia in gestational diabetes.
• However, overall, low-carb diets do not result in clear differences in gestational diabetes vs. flexible carbohydrate diets.

SAN DIEGO — Adherence to a low-carbohydrate diet during pregnancy may have some benefits in gestational diabetes, but overall, low-carbohydrate diets are not associated with any significant differences in outcomes, according to two experts.

During a debate at the American Diabetes Association Scientific Sessions, Amy M. Valent, DO, MCR, associate professor in the division of maternal-fetal medicine in the department of obstetrics and gynecology at Oregon Health & Science University, said identifying gestational diabetes and treating it, and the quality of carbohydrates in one’s diet, improves perinatal outcomes. She said the recommended dietary allowance of carbohydrates for pregnant individuals is at least 175 g per day because glucose is imperative in healthy fetal development. However, according to Valent, historical data have demonstrated that a lower-carbohydrate dietary plan can decrease glycemia, which may reduce the risk for some pregnancy complications among people with gestational diabetes.

“Based on the last 100 years of diabetes research in pregnancy, we’ve been focused on reducing overall blood sugars. The primary target for people with gestational diabetes has been dietary, and that approach has been low carbohydrates, which has been able to decrease perinatal mortality to the level that we are at today,” Valent told Healio.

Teri L. Hernandez, PhD, RN, associate dean of research and scholarship in the College of Nursing and professor in the department of medicine and the division of endocrinology, metabolism and diabetes at the University of Colorado Anschutz Medical Campus, agreed that the first line of therapy with gestational diabetes is nutrition. However, Hernandez said, low-carbohydrate diets are not the only approach in gestational diabetes treatment with nutrition.

“There’s no clear difference in primary outcomes between reduced carbohydrate meal plans and those that are more flexible in carbohydrate,” Hernandez said during the debate.

Benefits of a low-carb diet in pregnancy

Currently, dietary advice for treating gestational diabetes is inconsistent, and current professional guidelines have limitations and biases, according to Valent. Different diet strategies include low-carbohydrate, low glycemic index and total energy restriction eating plans, according to Valent. Valent said ACOG guidelines recommended a low-carbohydrate diet for gestational diabetes until the most recently revised edition in January.

Valent reviewed several major landmark studies demonstrating that gestational diabetes treatment can decrease pregnancy complications such as preeclampsia and large for gestational age infants.

“These studies were in the era where treatment of diabetes in pregnancy involved recommending a low-carbohydrate diet,” Valent said. “The concern with lowering carbohydrates is the risk of consuming lower nutrient-dense foods and resulting in the body to produce ketones, which may be associated with negative effects on the developing baby.”

In the Maternal-Fetal Medicine Unit (MFMU) multicenter, randomized trial published in The New England Journal of Medicine, 96% of pregnant women included in the study received nutritional counseling and diet therapy. This was associated with lower birth weight, neonatal fat mass, large for gestational age, macrosomia, shoulder dystocia, cesarean delivery, preeclampsia and gestational hypertension.

The Australian Carbohydrate Intolerance Study in Pregnant Women (ACHOIS), which individualized dietary advice with a dietitian and assessed individual dietary intakes, demonstrated that this strategy was associated with lower perinatal complications, birth weight, large for gestational age and macrosomia.

Trial results published in Diabetes in 1991 showed a correlation between carbohydrate percentage and postprandial glucose level at 1 hour. Results also showed that having a carbohydrate target of less than 140 mg/dL was associated with a 45% carbohydrate intake at breakfast, 55% at lunch and 50% at dinner. However, having a carbohydrate target of less than 120 mg/dL was associated with overall lower intakes, with 33% at breakfast, 45% at lunch and 40% at dinner.

A 2013 study published in Diabetes Care compared ketonuria percentage among pregnant women with gestational diabetes following a 55% carbohydrate diet or a 40% carbohydrate diet. According to Valent, findings showed no differences in ketonuria between the two groups.

An Australian study assessing a 6-week intervention with a low-carbohydrate diet (180-200 g) or an absolute low-carbohydrate diet (135 g) found low compliance: 65% of pregnant women in the moderate-carbohydrate group and 20% of pregnant women in the low-carbohydrate group stuck to their assigned eating plan. There was no difference in macronutrient intake between groups nor were there differences in HbA1c, fasting glucose, postprandial glucose or insulin use, Valent said. However, results demonstrated a difference in neonatal head circumference with smaller heads among the absolute low-carbohydrate group compared with the low-carbohydrate group (33.9 cm vs. 34.9 cm).

“Pregnancy is dynamic. Nobody’s the same today as they were yesterday. They’re going to be different 1, 2 or 3 weeks from now, and the nutritional demands and the fetal growth and development stage are going to be different,” Valent said. “So, nutritional demands are going to vary.”

According to Valent, further studies are needed to determine the quality of carbohydrate and not just the quantity of the carbohydrate on their effects in pregnancy outcomes.

Carbohydrate flexibility in gestational diabetes

A higher carbohydrate,complex carbohydrate eating plan is neither superior nor inferior to a low-carbohydrate diet, according to Hernandez; following a flexible carbohydrate meal plan during pregnancy contributes to a healthy mother and fetus.

In a flexible carbohydrate meal plan, a person reduces simple sugars while increasing their overall diet quality and complex carbohydrate intake, Hernandez said.

A 2018 meta-analysis published in Diabetes Care evaluated 18 randomized controlled trials of 1,151 pregnant women with gestational diabetes and found that any nutrition pattern modification after gestational diabetes diagnosis was associated with reduced maternal fasting and postprandial glucose by 4 mg and 8 mg. However, the quality of the evidence in the meta-analysis was low.

A Cochrane systematic review from 2017 included 19 randomized controlled trials that assessed different dietary advice for pregnant women with gestational diabetes and found no differences in outcomes. According to Hernandez, evidence in the review was limited because of the challenges of adherence in nutritional studies; medication being associated with one or more metabolic outcomes; phenotypic heterogeneity; inadequate power; inconsistent BMI reports; and reports of weight gain as total gestational weight gain, instead of weight gained during the nutrition intervention period.

Hernandez also noted that other randomized controlled trials reported lower postprandial glucose levels, reduced need for insulin, reduced weight gain and reduced macrosomia among pregnant women with gestational diabetes who followed low glycemic index carbohydrate diets. One study enrolled 140 Asian women who were admitted to a metabolic ward. They were randomized to either a diet in which a rice staple was replaced with a low glycemic option, or they were administered a diet with typical white rice. After 5 days, women in the low glycemic index-staple group had larger improvements in fasting and postprandial glucose vs. those in the regular diet group. Across five low glycemic index carbohydrate trials, researchers observed a reduced need for insulin, reduced weight gain and reduced macrosomia.

In the 6-week MAMI study published in The American Journal of Clinical Nutrition, researchers randomly assigned pregnant women with gestational diabetes to 135 g absolute carbohydrates per day or 180 to 200 g per day. Researchers noted no difference in ketones or glycemia between groups and no difference in macronutrient intake within or between carbohydrate groups.

In Hernandez’s own study, she and colleagues provided all nutrition to their study participants and participants were randomly assigned to follow a low-carbohydrate diet of 40% carbohydrates and 25% fat or higher-carbohydrate diet of 60% complex carbohydrates and 25% fat. Women in the higher-complex carbohydrate group ended up with 316 g carbohydrates per day vs. 214 g among women in the low-carbohydrate group. Hernandez and colleagues found no differences in 24-hour glycemia between the two groups, as both responded to their respective diets from 30 to 37 weeks. Women in both low- and high-carbohydrate diet groups demonstrated similar neonatal adiposity (P > .05) and good glycemic control (P > .05) that showed improvement over time. Time in range for both groups was about 92% with no between-group differences.

“The evidence that we have supports room for improvement in our guidelines for nutritional therapy for gestational diabetes,” Hernandez told Healio. “They show that low-carbohydrate diets are not superior to other diet patterns, including those that are more flexible with carbohydrate content, but also that diets that are more flexible [can] control glycemia to our current metrics and control fetal overgrowth.”

Hernandez also added that women and girls tend to be priced out of good nutritional patterns, which is an issue not only in the pregnancy field, but also in the global community. According to Hernandez, it is important to create ways moving forward to identify what nutritional patterns are best that are also affordable for families, especially in lower-income settings.

“There’s more to do, perhaps in real-world settings to address cultural acceptability and cost, but the evidence that we have is a good platform from which we can move forward,” Hernandez said.

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