Can Early Nutrition Be Responsible for Future Gut Microbiota Changes and Different Health Outcomes?

Background/Objectives: Chronic inflammatory diseases (CIDs) often present a preclinical phase influenced by genetic and environmental factors, including nutrition. Early dietary habits may modulate long-term health trajectories by shaping the intestinal microbiota. Previous work showed that weaning with fresh foods from the Mediterranean diet (MD) improved dietary habits and microbiota composition at 3 years of age. This study aimed to assess whether such benefits persist at 9 years. Methods: This long-term follow-up included 191 children (96 MD, 95 controls) from the original randomized cohort (ClinicalTrials.gov NCT05297357). The primary endpoint was adherence to MD (KidMed score ≥ 8). Secondary endpoints included BMI, incidence of CID, maternal dietary adherence, and intestinal microbiota composition in a subset of 36 children. Results: At 9 years, no difference was found in overall MD adherence (27.4% controls vs. 27.1% MD; p > 0.99) or BMI (17.7 vs. 18.1 kg/m²; p = 0.384). However, children from the MD group reported higher daily vegetable intake (71.9% vs. 51.6%; p = 0.005). Microbiota analyses revealed persistent differences between groups, with higher alpha diversity in the MD group. Although not statistically significant, the MD group showed lower prevalence of atopic dermatitis, allergic rhinitis, autism spectrum disorder, and ADHD. Maternal adherence to MD did not differ between groups. Conclusions: Early introduction of Mediterranean-style foods during weaning exerts lasting effects on dietary patterns and gut microbiota, with a potential protective trend against CID. While overall MD adherence converged between groups by 9 years, these findings suggest that early-life nutritional interventions may induce durable microbiome-mediated benefits and contribute to preventive strategies for chronic disease, warranting confirmation in larger, extended cohorts. Moreover, this study highlights the value of the collaboration between the Italian primary care pediatric system and the integration of the pediatric residency program, demonstrating a feasible and cost-effective methodology to generate large-scale prospective data within routine clinical practice. Larger studies and a longer follow-up period are necessary to confirm these results.