Nutritionist-Guided Video Intervention Improves Adherence to Mediterranean Diet and Reduces the Rate of Gestational Diabetes Mellitus: A Randomized Clinical Trial

Aims: Gestational diabetes mellitus (GDM) represents an increasing global challenge. Mediterranean diet interventions have proven benefits, but their implementation is limited by the absence of nutritionists in many public health systems. This study aimed to evaluate whether a video intervention guided by a nutritionist could increase compliance to Mediterranean diet and reduce the incidence of GDM and adverse maternal–neonatal outcomes. Methods: In this randomized controlled trial, 1750 consecutive pregnant women were allocated (1:1) to standard care (verbal, printed advice) or to a video designed by a nutritionist promoting a Mediterranean and physical activity. The primary outcome was the incidence of GDM; secondary outcomes included other pregnancy-related complications. Dietary adherence was assessed using the 14-item Mediterranean Diet Adherence Screener (MEDAS) score. Results: The experimental group increased their MEDAS score from baseline to GDM screening (mean difference (95% CI) 0.41 (0.23; 0.60); p < 0.001), mainly through greater extra virgin olive oil and nut intake and lower consumption of juices and confectionery. GDM incidence declined from 25.1% to 20.7% (p = 0.025), with significant reductions in gestational hypertension, episiotomy and neonatal intensive care unit admissions. Conclusions: Nutritionist-guided video intervention improves adherence to Mediterranean diet and reduces GDM incidence and adverse outcomes. This low-cost, scalable approach may help overcome structural limitations in public health systems.