Efficacy of Mediterranean Diet for the primary prevention of autoimmune diseases: A systematic review and meta-analysis featured in the Italian National Guidelines "La Dieta Mediterranea".

The Mediterranean Diet (MD) has been associated with reduced inflammation and improved immune regulation, suggesting a potential protective role against autoimmune diseases. This review was conducted in accordance with PRISMA 2020 and MOOSE guidelines. A comprehensive search of PubMed/MEDLINE, Scopus, Embase, and Cochrane Library was performed up to February 28, 2024. Study quality was assessed using the Newcastle-Ottawa Scale, and the certainty of evidence was evaluated with the NUTRIGRADE approach. Pooled effect sizes were computed using a random-effects model and expressed as risk ratios (RR), hazard ratios (HR), or odds ratios (OR), as appropriate. A total of 9 high-quality studies were included. No significant associations were found between high vs. low MD adherence and the incidence of rheumatoid arthritis (RR = 0.99, 95% CI: 0.97-1.01), lupus (HR = 0.97, 95% CI: 0.91-1.03), Crohn's disease (RR = 0.95, 95% CI: 0.84-1.07), or ulcerative colitis (RR = 1.02, 95% CI: 0.97-1.08). A significant inverse association was observed for multiple sclerosis (RR = 0.91, 95% CI: 0.85-0.98) and for Sjögren's syndrome (OR = 0.81, 95% CI: 0.66-0.99). However, the certainty of evidence for all outcomes was rated as low. Promising associations were observed for multiple sclerosis and Sjögren's syndrome, although current evidence does not support a consistent protective effect of the MD across several other autoimmune diseases. Further longitudinal research is needed to confirm these findings and explore underlying mechanisms. Meanwhile, the promotion of MD adherence remains justified within broader public health strategies for chronic disease prevention.