Does the acid in tomatoes affect arthritis?

No because RA is autoimmune disease and this is caused by genetic factors effecting the immune system, however there could be some effect depending on the individual, on the arthritis that is a result of RA. I have found In my particular case that Acidy foods don't make any particular difference to my condition. I have found from time to time that certain fruits and red wines and port can cause some discomfort if I have a lot. but the affects are not consistent. there is no scientific evidence that diet has any affect on Arthritis of any kind other then Gout.