The use of fish, particularly fatty fish and fish oil, to support or treat rheumatoid arthritis (RA) is justified by scientific evidence. Numerous studies have investigated the effects of omega-3 polyunsaturated fatty acids (PUFAs), primarily eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), found in fish and shellfish, on inflammatory conditions like RA. Meta-analyses and randomized controlled trials have demonstrated that omega-3 supplementation can lead to modest but meaningful reductions in joint pain, morning stiffness, and the number of tender joints in people with RA. The proposed mechanism involves the anti-inflammatory properties of omega-3 PUFAs, which compete with pro-inflammatory omega-6 fatty acids, leading to decreased production of inflammatory eicosanoids and cytokines.

For example, a 2017 Cochrane review concluded that fish oil supplementation probably reduces pain and improves patient-reported global assessment of disease activity, although the effects are moderate and not all patients respond. Dietary guidelines for people with RA commonly recommend regular consumption of fatty fish (such as salmon, sardines, and mackerel) or fish oil supplements as part of an anti-inflammatory diet. Shellfish contain lower amounts of omega-3s, but still contribute beneficially.

While fish is not a cure for RA and should not replace conventional treatments, the scientific consensus supports its adjunctive role in symptom management and possibly in slowing disease progression.