Background and Objectives: This study investigated the impact of nutritional status and foods consumed on inflammation and disease activity in patients with rheumatoid arthritis (RA). Materials and Methods: We designed a cross-sectional observational study, involving 110 patients diagnosed with RA. The patients included were between 18 and 75 years old, diagnosed with rheumatoid arthritis two years ago or earlier, with stable treatment for the last 8 weeks. Data on anthropometric parameters, body mass composition, nutritional status, individual food consumption records, inflammation, disease activity, quality of life, clinical, and laboratory parameters were collected for each study participant. The evaluation parameters of the patients were the simple disease activity index (SDAI), clinical disease activity index (CDAI), systemic immune-inflammation index (SII) and individual food consumption records. A bioimpedance device and measuring tape were used to take body composition and anthropometric measurements of the patients. Results: According to the body mass index, waist circumference and waist-to-height ratio, in our study, we found that 60% of the patients were obese, 80% were at a very high health risk, and approximately 91% were in need of nutritional treatment. There was a significant negative correlation between the dietary intake of total energy, total fat, omega 3, calcium, zinc, cobalamin and the disease activity (SDAI, CDAI). There was a significant negative correlation between polyunsaturated fatty acids, omega 3, carotene, vitamin E, selenium and the SII. Additionally, there was a positive correlation between omega 6 and the SII, SDAI, CDAI (p < 0.05). Conclusions: The results of this study show that the foods consumed in the nutrition of RA patients may have effects on their inflammation and disease activity.