The Role of Microbiome and Diet on Disease Activity and Immune–Inflammatory Status in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease of autoimmune background and unknown etiology. The importance of genetic factors in RA development is well-established. Environmental factors have also been extensively researched in relation to risk of RA and managing its symptoms. Smoking, physical activity, diet, and gut microbiota are considered to be the most essential modifiable factors in RA. Among dietary interventions, the most researched is Mediterranean diet, monounsaturated fatty acids, fish consumption, and fish oil (EPA, eicosapentaenoic acid and DHA, that is, docosahexaenoic acid). Others concerned gluten-free and vegan or vegetarian diet, salt intake, supplementation with vitamin D, antioxidants, prebiotics, and probiotics. Diet modifications can alter the gut environment, and the association between RA development or severity and the composition of gut bacteria has already been shown. This review focuses on effectiveness and usefulness of various dietary approaches and supplements in RA prevention and management, including the influence on disease activity and inflammatory status. The composition of gut microbiota and its changes in response to dietary factors are also considered. There is a great need for further research into mutual dependencies of diet, microbiome, and RA activity. The current state of knowledge provides promising evidence for future nutrition and microbial therapies.