In this study, it is aimed to determine the effect of the DASH diet model on the treatment of patients with seropositive rheumatoid arthritis, by evaluating its potential impact on inflammatory markers, disease activity scores, patients' functional status in daily life, and quality of life.

"This study is being conducted as part of a doctoral dissertation, and due to insufficient initial awareness regarding the requirement for prior registration, the registration process was completed after data collection had already begun. However, data collection is still ongoing, and the study has not yet been completed. We remain committed to full compliance with clinical trial reporting standards and transparency."

Prior to the commencement of the study, participants will be informed about the research, and those who voluntarily agree to participate will be asked to sign an informed consent form. This study, designed to determine the effect of the DASH diet on treatment outcomes in patients diagnosed with seropositive rheumatoid arthritis (RA), will collect data through a questionnaire including participants' demographic characteristics (gender, age, marital status, education level, occupation, income status), health status (duration of treatment, RA symptoms, presence of RA in relatives, use of medications and nutritional supplements, history of any RA-specific nutritional or diet therapy, presence of any chronic diseases other than RA, pregnancy/lactation status in RA patients), dietary habits (number of main and snack meals, reasons for meal skipping, foods consumed during snacks, average daily water intake, smoking and alcohol consumption), functional status in daily life, quality of life, food consumption frequency, and a 3-day dietary record. Additionally, numerical data including patients' 24-hour physical activity level, DAS-28 disease activity score, VAS general health assessment, VAS pain score, anthropometric measurements (body weight, height, and BMI), and basal metabolic rate (BMR) will be obtained.The DASH diet prescribed to patients in the intervention group will be planned according to their 24-hour physical activity level and BMR. The DASH diet adherence score will be calculated using the "Nutrition Information System (BeBiS)" program, based on the patients' dietary intake records including average daily intake of total fat, saturated fat, protein, cholesterol, fiber, magnesium, calcium, sodium, and potassium. Biochemical findings of the patients will be obtained from the patient information system with physician approval.This randomized controlled trial is planned to implement the DASH diet intervention for 3 months (12 weeks), considering similar studies in the literature, to observe the expected differences in patients with seropositive rheumatoid arthritis in the intervention group. Patients in the control group will continue their usual diet without any specific dietary intervention. Relevant data from individuals in both the intervention and control groups will be collected again at the end of weeks 4, 8, and 12 following the dietary intervention.

Inclusion Criteria:

• Voluntary acceptance to participate in the study, Being within the age range of 18-64 years, Having a diagnosis of rheumatoid arthritis according to the 2010 American College of Rheumatology (ACR)/European League Against Rheumatism (EULAR) classification criteria and belonging to the seropositive rheumatoid arthritis subgroup, Being in the active phase of rheumatoid arthritis according to the DAS-28 CRP or DAS-28 ESR disease activity score, Having a disease duration of at least 1 year, Not having previously undergone any dietary treatment specific to rheumatoid arthritis, Not using any dietary supplements other than calcium and vitamin D3 supplementation (e.g., 1000 mg calcium, 880 IU vitamin D3) recommended by the physician for patients using glucocorticoids and folic acid supplementation (10 mg weekly) recommended for patients using methotrexate, Having stable use of disease-modifying anti-rheumatic drugs (≥3 months), corticosteroids (≥4 weeks), and nonsteroidal anti-inflammatory drugs (≥10 days) before starting the DASH diet treatment, with a daily oral corticosteroid dose not exceeding 12.5 mg of prednisolone, Not having a diagnosis of eating disorders, Not being pregnant or breastfeeding, Not using banned substances, Having no intellectual disability, Having no allergy and/or intolerance to the foods included in the DASH diet

Exclusion Criteria:

• Not voluntarily agreeing to participate in the study, Not being within the age range of 18-64 years, Not having a diagnosis of rheumatoid arthritis according to the 2010 American College of Rheumatology (ACR)/European League Against Rheumatism (EULAR) classification criteria, and not belonging to the seropositive rheumatoid arthritis subgroup, Being in remission according to the DAS-28 CRP and DAS-28 ESR disease activity scores, Having a disease duration of less than 1 year, Having previously undergone any dietary treatment specific to rheumatoid arthritis, Using any dietary supplements other than calcium and vitamin D3 supplementation (e.g., 1000 mg calcium, 880 IU vitamin D3) recommended by the physician for patients receiving glucocorticoid therapy and folic acid supplementation (10 mg weekly) recommended for patients using methotrexate, Having changes in disease-modifying anti-rheumatic drugs usage within less than 3 months, corticosteroids within less than 4 weeks, and nonsteroidal anti-inflammatory drugs within less than 10 days before starting the DASH diet treatment, having a daily oral corticosteroid dose exceeding 12.5 mg of prednisolone, Having a diagnosis of eating disorders, Being pregnant or breastfeeding, Using banned substances, Having intellectual disability, Having any allergy and/or intolerance to the foods included in the DASH diet.

This is an open-label study. No masking was applied, as both participants and investigators were aware of the group assignments due to the nature of the dietary intervention.