Extra Virgin Olive Oil Supplementation in Gestational Diabetes: Insights from the OLIDIAG Randomized Trial

Key Takeaways:

• Daily extra virgin olive oil (EVOO) intake significantly reduced the need for insulin therapy in women with gestational diabetes mellitus (GDM).
• Maternal triglyceride levels improved without affecting weight gain or overall glycemic control, suggesting a targeted metabolic benefit.
• Neonatal outcomes showed meaningful improvements, including fewer multiple complications and reduced NICU admissions.

Dietary management remains a cornerstone of care for gestational diabetes mellitus, yet the optimal composition of that diet continues to evolve. A multicenter randomized clinical trial conducted across Argentina—the OLIDIAG study—offers new evidence that a simple nutritional intervention, supplementation with extra virgin olive oil, may meaningfully influence both maternal metabolism and neonatal outcomes.

The trial enrolled 190 pregnant women diagnosed with GDM before 29 weeks’ gestation, randomly assigning them to standard care or to an intervention that included three daily tablespoons (approximately 36 grams) of EVOO. As illustrated in the study flow diagram on page 3, 140 participants completed the study with third-trimester data available, forming the basis for outcome analysis. Adherence to the intervention was notably high, with more than 80% of participants maintaining consistent intake.

The primary findings point to a clinically relevant metabolic effect. Women in the EVOO group experienced a significant reduction in insulin requirements during pregnancy. When evaluated after initiation of the dietary intervention, insulin use dropped from 40.9% in the control group to 24.3% in the intervention group, corresponding to a roughly 40% relative risk reduction. Moreover, time-to-event analysis showed that women receiving EVOO remained free from insulin therapy for longer durations, with more than half never requiring insulin by delivery.

This improvement occurred alongside a marked reduction in maternal triglyceride levels—approximately 43 mg/dL lower than controls—without significant changes in gestational weight gain or overall glycemic markers such as HbA1c. These findings suggest that EVOO may exert a targeted effect on lipid metabolism and insulin sensitivity rather than broad changes in glucose control. The reduction in the triglyceride-to-HDL ratio, a surrogate marker of insulin resistance, further supports this interpretation.

Mechanistically, these effects align with the known properties of EVOO. Rich in monounsaturated fatty acids—particularly oleic acid—and polyphenols, EVOO has been shown in prior studies to exert anti-inflammatory and antioxidant effects, as well as to modulate metabolic pathways through nuclear receptor activation. The current trial extends these observations into the context of pregnancy, where metabolic regulation is uniquely complex.

Maternal clinical outcomes, however, remained largely unchanged. Rates of hypertensive disorders, cesarean delivery, and other obstetric complications did not differ significantly between groups. This may reflect the relatively good baseline metabolic control achieved in both arms through standardized care and frequent clinical follow-up.

The most compelling secondary findings emerged in neonatal outcomes. While the overall composite of neonatal complications did not differ significantly, the intervention group showed a substantial reduction in more severe presentations. Specifically, the proportion of neonates experiencing more than one complication decreased by two-thirds, and NICU admissions were reduced from 18.2% to 6.8%. These benefits were particularly pronounced among infants with hypoglycemia, where the need for intensive care was markedly lower.

Although the mechanisms underlying these neonatal improvements remain speculative, they may relate to improved intrauterine metabolic conditions or direct effects of maternal diet on placental function. Prior translational and preclinical studies cited by the authors suggest that EVOO may reduce placental inflammation and oxidative stress, potentially influencing fetal development.

Several limitations temper the findings. The study was not blinded, introducing the possibility of performance bias, and a relatively high dropout rate may affect generalizability. Additionally, the lack of strict intention-to-treat analysis and absence of objective biomarkers of EVOO intake warrant cautious interpretation.

Even so, the OLIDIAG trial provides some of the most robust clinical evidence to date supporting a specific dietary modification in GDM management. In an area where interventions are often complex or resource-intensive, the simplicity and accessibility of EVOO supplementation may offer a practical adjunct to standard care.

As gestational diabetes continues to rise globally, integrating evidence-based nutritional strategies into routine practice could help reduce both maternal treatment burden and neonatal risk—an outcome that resonates well beyond pregnancy itself.