Objective:  The historic practice of advising a low-carbohydrate, thus higher-fat, diet in the management of gestational diabetes mellitus(GDM) has not been sufficiently tested. In addition to glucose, high maternal triglycerides(TG) and free fatty acids(FFA) are independent risk factors for fetal macrosomia and excess neonatal adiposity. This study tested the hypothesis that a high-complex carbohydrate/lower fat diet would result in higher postprandial(PP) glucose excursions, but an overall 24-hour glucose area-under-the-curve(AUC) that is no different or lower than that of a low-carbohydrate/higher fat diet.

Design: Randomized cross-over study

Setting: Clinical Translational Research Center(CTRC)

Patients/Participants: Women with diet-controlled GDM

Methods: Women with diet-controlled GDM consumed a high complex-carbohydrate/low-fat diet(HC/LF; 60% CHO, 25% fat, 15% protein) and a low-carbohydrate/higher fat diet(LC/HF; 40% CHO, 45% fat, and 15% protein) for 3 days each (washout in between) while wearing a continuous glucose monitor(CGM). On day-4 of each diet, PP lipemia was measured hourly(5 hrs) after women consumed breakfast(30% of total daily calories). All food was provided by the CTRC. A paired t-test was used for difference testing.

Results:  Ten women with GDM (Mean±SEM; body mass index 33.6±1.5kg/m²; age 29±1yrs; 30.4±0.5wks gestation) completed the diet cross-over. While CGM revealed no difference in mean nocturnal blood glucose(BG) or fasting BG(p>0.05), the HC/LF diet yielded a modestly higher: mean 24-hr BG(96.3±3.4 vs. 90.3±3.8mg/dL, p=0.03, respectively), mean 24-hr AUC, and mean PP 2-hr AUC across meals(p<0.005). One-hr and 2-hr PP glucose by CGM was higher across meals on the HC/LF diet compared to the LC/HF diet(115±3 vs. 106±3mg/dL [p=0.009], and 108±5 vs. 98±3mg/dL [p=0.01], respectively). On day-4, there were no differences in fasting plasma glucose, insulin, TG, or FFA. Postprandial blood analyses revealed: higher 5-hr AUC for glucose and insulin on the HC/LF diet(p=0.004 for both), no difference in the 5-hr TG AUC, but a higher 5-hr FFA AUC on the HF/LC diet(p=0.005).

Conclusion/Implications for nursing practice: The pattern of glycemia on both diets was remarkably similar. Despite modestly higher glucose concentrations on the HC/LF diet, both diets easily met current recommendations (<140 and <120mg/dL at 1- and 2-hrs PP; mean BG 87-104mg/dL). Thus, nurses may be able to help women with GDM consume a more balanced diet (in carbohydrate/fat) while still meeting glycemic targets. The consistently higher FFAs on the LC/HF diet could worsen maternal insulin resistance and augment neonatal adiposity. Further investigation is required to understand the importance of balancing dietary carbohydrate and fat by its metabolic effects on both mother and offspring.

Keywords:  GDM, Diet, Carbohydrate