A Nutrition Intervention for Arthritis -4 (WCCR-ARTH4)

Inclusion Criteria: * A diagnosis of rheumatoid arthritis based on 2010 ACR / EULAR Rheumatoid Arthritis Classification Criteria. Classification as "definite RA" is based on: * the confirmed presence of synovitis in at least 1 joint * absence of an alternative diagnosis that better explains the synovitis * and achievement of a total score of 6 or greater (of a possible 10): 24 Joint involvement, designating the metacarpophalangeal joints, proximal interphalangeal joints, the interphalangeal joint of the thumb, second through third metatarsophalangeal joint and wrist as small joints, and elbows, hip joints and knees as large joints: 1. Involvement of 1 large joint gives 0 points 2. Involvement of 2-10 large joints gives 1 point 3. Involvement of 1-3 small joints (with or without involvement of large joints) gives 2 points 4. Involvement of 4-10 small joints (with or without involvement of large joints) gives 3 points 5. Involvement of more than 10 joints (with involvement of at least 1 small joint) gives 5 points * Serological parameters - including the rheumatoid factor as well as anti-citrullinated protein antibody (ACPA): 1. Negative RF and negative ACPA gives 0 points 2. Low-positive RF or low-positive ACPA gives 2 points 3. High-positive RF or high-positive ACPA gives 3 points Acute phase reactants: 1 point for elevated erythrocyte sedimentation rate (ESR) or elevated C-reactive protein (CRP) value Duration of arthritis: 1 point for symptoms lasting six weeks or longer * Continuing or recurring pain (i.e., joint pain daily, unless on pain medication). * Age at least 18 years * Ability and willingness to participate in all components of the study * Willingness to be assigned to either the diet group or supplement group * Pain medications unchanged within last 6 weeks. Exclusion Criteria: * \< 18 years of age * Alcohol consumption of more than 2 drinks per day or the equivalent, episodic increased drinking (e.g., more than 2 drinks per day on weekends), or a history of alcohol abuse or dependency followed by any current use * Use of recreational drugs in the past 6 months (past drug use, if fully recovered, is not a criteria for exclusion) * Pregnancy * Unstable medical or psychiatric illness * Likely to be disruptive in group sessions (as determined by research staff) * Already following a low-fat, vegan diet * Lack of English fluency * Inability to maintain current medication regimen * Inability or unwillingness to participate in all components of the study