OLIDIAG Study: Extra Virgin Olive Oil Supplementation in the Diet of Women with Gestational Diabetes Mellitus—A Randomized Clinical Trial

Background/Objectives: Gestational diabetes mellitus (GDM) is a prevalent metabolic disease associated with maternal and neonatal complications. Diets enriched with extra virgin olive oil may benefit metabolism and provide antioxidant effects. We aimed to evaluate the effects of dietary supplementation with extra virgin olive oil on metabolic parameters and insulinization rate in women with GDM. Methods: This is a multicenter, parallel, randomized controlled trial in which 190 patients with GDM were enrolled before week 29 of gestation and randomized into the Control group and the Intervention group. Patients in the Intervention group received the indication to consume three tablespoons of extra virgin olive oil (EVOO) daily. At term, metabolic parameters, insulin requirement and maternal and neonatal outcomes were evaluated. Results: Control and Intervention groups showed no differences in maternal age (31.7 ± 6.0 and 32.4 ± 5.2 years, respectively) or gestational age (26.5 ± 3.6 and 26.7 ± 3.3 weeks, respectively) at enrollment. Primary outcomes showed that EVOO consumption was associated with a reduction in insulin requirement (RR 0.595, 95% CI 0.361–0.967, p < 0.05). There was a significant reduction in triglyceridemia in the EVOO-supplemented group compared to controls (MD −43.3 mg/dL, 95% CI −66.8–−19.8, p < 0.01). There were no effects of the intervention on gestational weight gain. As secondary outcomes, maternal BMI and gestational age at delivery showed no changes between the groups. Although maternal and neonatal composite outcomes were not significantly reduced, the rate of neonates with more than one complication (RR 0.340, 95% CI 0.133–0.870, p < 0.05) and NICU requirement (RR 0.367, 95% CI 0.140–0.939, p < 0.05) were significantly reduced in the Intervention group. Conclusions: In GDM, maternal dietary supplementation with extra virgin olive oil resulted in reduction in maternal triglyceridemia, need of insulinization and neonatal complications.