Diets that restrict carbohydrate intake, such as the low-carbohydrate diet or the ketogenic diet (KD), have gained popularity as potential dietary interventions for glycemic control in non-pregnant individuals with diabetes.1,2 Results among those with gestational diabetes (GDM), however, are conflicted.
Ketogenic Diets During Pregnancy
Current dietary guidelines by the American Diabetes Association based on Dietary Reference Intakes recommend at least 175 g of carbohydrates daily during pregnancy in women with GDM.3 Thus, dietary interventions that restrict carbohydrate consumption such as the KD are not currently promoted during pregnancy.1,4 These concerns are based on prior research suggesting that low-carbohydrate diets may increase maternal ketone levels, which may be associated with poor fetal and childhood outcomes.2
Maternal Ketone Physiology – Ketones are produced when lipids are broken down by the liver.2 When there is decreased glucose availability, the body increases the production of ketones as an alternate form of energy, a process known as ketogenesis. Ketogenesis is naturally accelerated when consuming diets that restrict carbohydrate intake and during the third trimester of pregnancy. Maternal and fetal ketone levels are directly linked as maternal ketones are shared with the fetus through the placenta.
Current Research – Although more research is needed to determine what degree of carbohydrate restriction increases ketone levels and what level of ketones may be harmful in pregnancy, concerns remain over carbohydrate restriction during pregnancy.2 Current research on the effects of low-carbohydrate diets in GDM are limited and conflicted. Older studies have discussed that elevated maternal ketone levels may be associated with low IQ in children, but no fetal malformations have been linked with maternal ketones. Research done in mice have shown that mice fetal brain development may be affected by KDs, but it is unclear how this is translated to human brain development. There has not yet been clear evidence suggesting that increased maternal ketones directly cause negative fetal outcomes.
A 2019 review of high-quality systematic reviews on dietary interventions for GDM noted that KDs have not yet been studied in women with GDM as a primary nutrition therapy.5 Studies found no particular advantages between low-carbohydrate and energy-restricted diets in maternal or neonatal outcomes. The review noted that diets that restrict carbohydrate intake may foster anxiety in mothers and unintentionally increase consumption of saturated and processed fats, which may increase maternal free fatty acids and prolong postprandial hyperglycemia. Recent evidence suggests that this may stimulate fetal overgrowth and fat accumulation, requiring individuals to carefully weigh the potential risks when utilizing carbohydrate restriction. The review concluded that diets with low glycemic index foods, regardless of whether it is a low-carbohydrate or a calorie-restricted diet, may improve maternal and neonatal outcomes such as rates of insulin use and macrosomia.
Special Caution: Diabetic Ketoacidosis
Diabetic ketoacidosis (DKA) is a serious complication considered particularly dangerous during pregnancy as it is associated with adverse fetal outcomes and high rates of perinatal morbidity and mortality.2,3 Research is yet unclear whether elevated ketone levels, acidosis, dehydration, or other confounding factors cause fetal harm, but individuals should be aware of the potentially increased risk of DKA with diets that restrict carbohydrate intake.
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