Rheumatoid arthritis (RA) is a systemic connective tissue disease which develops in the course of an autoimmune inflammatory process triggered by environmental factors in a genetically predisposed person. One of the environmental factors is the diet. RA patients’ adherence to a healthy diet remains low, despite plentiful data confirming positive effects of some foods, e.g. fish rich in n-3 polyunsaturated fatty acids (PUFAs), as well as the negative influence of unhealthy eating patterns, such as high consumption of fats and sugars, on RA incidence, activity and treatment response. In this review, we present current knowledge on the role of diet in rheumatoid arthritis, including dietary factors’ preventive/promoting influence on RA development, as well as their impact on RA activity. We hope this article will aid and encourage clinicians to recommend a relevant dietary intervention to their RA patients.