Dissertação de Mestrado Nutrição Humana e Metabolismo 2023 Faculdade de Ciências Médicas, Universidade NOVA de Lisboa

Introduction: Rheumatoid Arthritis (RA) is an autoimmune disease that leads to inflammation, cartilage and bone destruction, and malformation/destruction of multiple joints; affecting the physical and mental well-being and quality of life (QL) of patients. As remission is not always achieved with pharmacotherapy, dietetic intervention has been evaluated as an adjuvant therapy. Diet is an environmental factor that can influence inflammatory activity, change the lipid profile, increase antioxidant levels, and modulate the gut microbiota (also involved in the development of the disease). In this sense, studying a diet that combines all the components with an impact on RA is a priority to complement the prescribed treatment. Objective: The main objective of the present study was to investigate the effect of an anti inflammatory diet (AID) (characterized by the reduction of exposure to large proteins in the intestine, mainly gluten; specification of the most suitable vegetables; limitation of yogurts to those enriched with L. Casei; and by the daily intake of specific spices and seeds), compared to a control diet (Mediterranean Diet - MD), on disease activity (DA) and on the improvement of QL, in RA patients. Furthermore, the relationship of AID with clinical and anthropometric markers, and with the modulation of the composition of the intestinal microbiota, in comparison with MD, was analyzed. Methodology: This parallel randomized controlled clinical trial included 26 patients with RA followed in the autoimmune disease appointment at Hospital Particular do Algarve. They were randomized/allocated and educated to perform one of the two diets. The dietetic intervention lasted fifteen weeks and clinical, anthropometric and QL markers and a fecal sample was collected before and after the intervention. The composition of the intestinal microbiota was sequenced by 16S after extraction of genomic DNA from feces and the statistical treatment was performed using SPSS version 27. Results: It was found that the application of AID led to a greater reduce the Disease Activity Score 28 (DA) compared to MD, however, after eliminating the confounding factors, this reduction was not statistically significant between diets and both led to a moderate clinical response. About the Health Assessment Questionnaire (QL), the two interventions led to a similar reduction. MD induced an increase in beta diversity and a greater number of changes in microbiota composition. With DM, a decrease in the abundance of the phylum of Actinobacteria and Firmicutes and an increase in Bacteroidota was verified. As for the genus, there was an increase in Bacteroides, Bilophila, Lachnospiraceae_unclassified, Parabacteroides, Roseburia and Suterella and a reduction in Bifidobacterium, Subdoligranulum, Lachnospiraceae_ge and Collinsella. However, no differences were found between diets in terms of diversity after the intervention. When comparing the relative abundance of phylum and genus between diets at the end of the intervention, it was found that the phylum Deferribacterota and the genus Collinsella showed a significant difference and were found in greater amount in the AID participants. Conclusion: The results suggest that both interventions had a positive impact on DA, but the AID intervention had a greater impact compared to MD, and both diets had an effect on improving QL. The greater impact on the microbiota did not correspond to a superior improvement in the prognosis of the disease. In this way, changes in the microbiota did not seem to be the main significant etiologic agent in DA. This study reinforces the viability a dietetic intervention as an adjuvant therapy in patients with moderate DA, in particular, an AID-based intervention