Modestly lower carbohydrate diet not associated with improved outcomes related to gestational diabetes

1. A modestly lower carbohydrate diet neither increased ketonemia nor improved glycemic control in pregnant women

Evidence Rating Level: 2 (Good)

Although meta-analyses have shown significant improvements in HbA1c and greater weight loss with low-carbohydrate diets in the context of type 2 diabetes and obesity, there is a lack of consensus on the most effective diet for gestational diabetes (GDM). GDM is rising in prevalence and associated with adverse pregnancy outcomes, such as macrosomia and cesarean section. However, low-carbohydrate diets in pregnancy may increase maternal ketone concentrations, which have been associated inversely with offspring intelligence, even without ketoacidosis. Therefore, a modestly lower carbohydrate diet (MLC) was hypothesized to lower glucose levels without inducing ketonemia. MAMI I (Macronutrient Adjustments in Mother wIth gestational diabetes study I) was a six week, two-arm, parallel RCT conducted on pregnant women between 18-45 years old with a GDM diagnosis at 24-32 weeks of gestation. 46 patients were randomly allocated (stratified by age and BMI) to either a diet of 135g of carbohydrates/day or routine care, targeting 180-200g/day (RC), with allocation of treatment concealed from the dietician. Through a modified ITT analysis, no detectable differences in blood ketone concentrations (BHB) between the dietary groups were found (MLC 0.1+0.0, RC 0.1 +0.0, P=0.34).  According to their food diaries at the end of the trial, only 20% of the women in the intervention group met the carbohydrate target, while 66% of all participants had already developed some carbohydrate restriction at baseline. The intervention group had significantly lower dietary intakes of iron and iodine, with only a third of the women in the intervention group meeting nutrient reference values (MLC 32% vs RC 67% for iron, MLC 39% vs 89% for iodine). No differences were found in secondary outcomes, in weight or gestational age at delivery, fat mass, macrosomia, or large-for-gestational age infants. There was no difference in glycemia (MLC 6.1+ 0.1, RC 6.0+0.1mmol/L), nor was ketonemia found to be affected by exogenous insulin use (P=0.97). Though small changes in ketonuria are not considered clinically important, the final sample size had 77% power to detect a 0.04 mmol/L difference in BHB. More appropriately powered studies with larger sample sizes and food provision to increase dietary compliance are necessary to assess the benefits and risks associated with a modestly lower carbohydrate diet in GDM.

Click to read the study in the American Journal of Clinical Nutrition

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