Patients with RA will be studied to see whether meals of different content will affect inflammation and metabolic variables in the postprandial state. Healthy controls will also be invited to examine potentially different responses to patients with RA.

The PIRA study aims to evaluate the metabolic and inflammatory effects after a vegan meal or a meal containing red meat or fish in patients with RA and matched controls. The study have a cross-over design and each participant will have one of three meals every week and then be compared to themselves. In addition healthy individuals will be included for the red meat meal so that the response from this meal could be compared between patients with RA and their matched controls. Blood samples will be collected before the meal (fasting) and every hour until 5h. Primary outcome will be high sensitive IL-6. Secondary outcomes will be additional inflammation markers such as area under curve for hs-CRP and gene expression in PBMC:s regarding genes related to inflammation and, glucose, blood lipids and metabolomics-profile in serum and urine.

Inclusion Criteria for patients with RA:

• Diagnosed with rheumatoid arthritis
• BMI 18.5-30.0 kg/m2
• 2 years or more since diagnosis
• No DMARD changes during the last 3 months

Inclusion Criteria for healthy controls:

• Absence of diagnosis of RA
• BMI 18.5-30.0 kg/m2
• Self-assessed as healthy

Exclusion Criteria:

• Diagnosis of cancer, inflammatory bowel disease, celiac disease, diabetes
• Allergy or intolerance to any of the foods in the study
• Pregnancy or breastfeeding
• Use of any blood lipid lowering medication, glucocorticoids or IL-6-inhibitor during the last 4 weeks prior to enrolment
• Smoking
• Hemoglobin < 100 g/L

Data cannot be shared publicly because of Swedish law. The datasets analysed could be made available from the corresponding author on reasonable request.

All data will be given a new code Before statistical analysis to mask treatment (study meal or Control) to the outcome assessor