From that thread the response was to pursue an elimination diet, I quote:
"Unfortunately, if our patients have tried a strict gluten-free mcdougall diet and are still struggling with RA symptoms then the next step is an elimination diet. Some people get rid of corn and soy as well as gluten but it really depends on how quickly they want to figure this out vs. deal with some food deprivation. If you are struggling with doing an Elimination Diet on your own then ask your physician for help. Of course, you could see us or Dr. McDougall but it is important that you get your symptoms under control!"
I don't have it, I have his older book, but there are good reviews on Amazon. I can't see any claims of curing Arthritis in 12 days, I guess though that this will work if there are no complications.
There are also a couple of Star McDougallers that may interest you...
At the end of each lecture, Dr McD comments.
My best guess is for whoever is concerned to try the basic McDougall plan, if symptoms persist then try elimination. If that were me I'd want to do it in conjunction with a doctor who understands this stuff. There is a search facility at the McDougall website http://www.drmcdougall.com/doctors/
- but this covers USA only, sadly.
In the future, I think Dr Campbell will be making a list of Doctors who have been on his certificate course, at least that is the impression I get, having read the inside back cover of his latest prints of "The China Study". That may be a useful resource, if and when it arrives.