Fatty fish varieties such as salmon, mackerel, sardines and trout are high in omega-3 fatty acids, which have been found to have potent anti-inflammatory effects. In addition to this, fatty fish is also a good source of vitamin D. Multiple studies have found that rheumatoid arthritis may be associated with low levels of vitamin D, so it is definitely a wise decision for the people with arthritis to have fatty fish on their platters.