Results seem to be mixed, some studies show a positive effect, others no effect at all. The studies referenced by [Arthritis Research](http://www.arthritis.org/living-with-arthritis/arthritis-diet/anti-inflammatory/vegan-and-vegetarian-diets.php) suggest that going vegan seems to show better results than being vegetarian. Going vegetarian or vegan may have the additional benefit that you're more likely to [lose weight](http://www.eatthis.com/veganism-found-to-be-the-best-diet-for-weight-loss) over time which will put less strain on your joints. Most studies don't really run long enough to prove this though.

On the other hand, I suppose it's only fair to point out if you are thinking of becoming vegetarian and vegan solely for the above reasons that there is also evidence that the [consumption of oily fish](http://www.arthritisresearchuk.org/arthritis-information/complementary-and-alternative-medicines/cam-report/complementary-medicines-for-rheumatoid-arthritis/fish-oils.aspx) can improve the symptoms of rheumatoid arthritis.

On balance, changing your diet probably won’t have as great an impact on your arthritis as the medicine prescribed by your doctor will.