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Generally, rheumatoid arthritis is not aggravated, in any universally predictable fashion, by foods we eat. This is what research tells us.
Having stated that, it must be recognized that each human being is a complex organism and that we are each different. Anecdotally, a particular individual may notice worsening of symptoms after certain foods are eaten. This individual may, indeed, benefit by avoiding or limiting these foods.
Finally, researchers have also found that fish oils have inflammation - fighting properties. This is especially true of fishes in the salmon family. Eating diets that emphasize fish my benefit some patients with rheumatoid arthritis. Fish oil tablets are also available in health stores and pharmacies for this purpose. For more, read the Rheumatoid Arthritis article.