In regards to Rheumatoid Arthritis, I want to relate my experience using Conjugated Linoleic Acid (CLA).
When I eat dairy products especially milk and ice cream, I notice my RA DOES act up. When I eat the dairy with one tablet of CLA, my RA DOES NOT seem to act up.
I have found a supporting study that relates my personal experience
Milk has been anecdotally associated with an exacerbation of arthritic symptoms. A case study presented in the Arthritis and Rheumatism Journal found that some patients have an allergic response to milk that creates inflammation in the joints. Another study published in Arthritis Today magazine found that one compound in milk called conjugated linoleic acid actually reduced inflammation. Patients are advised to eliminate milk for one week to monitor symptom relief. In addition, milk and dairy products are rich sources of calcium and vitamin D which strengthen bones and prevent fractures and other bone concerns for those with osteoarthritis.
For people whose RA acts up but may desire to eat dairy products, this may be something to experiment with.
As an aside, CLA also does wonders for body fat management but each person is different in when they will respond. It took me nearly 7 months and others respond more very quick.
CLA got removed from the diet when they stopped using grass fed animals.