Just some thoughts on this...I've read a little bit about AS, and I believe it is classified as autoimmune and one of the rheumatological diseases, although different in ways...still, that like many of those diseases, and like just about all autoimmune diseases, it can also affect eyes, lungs, various organs, and may possibly also originate from leaky gut syndrome.
As I understand leaky gut syndrome, the openings in the small intestine that are supposed to let digested nutrients into the bloodstream become too large, and at the same time, it's possible some proteins are not adequately broken down, enter into the bloodstream and are attacked by the immune system. I have read that a hormone called zonulin is responsible for the size of the openings in our intestine...that too much zonulin causes the openings to become too wide, thus allowing undigested protein fragments to escape and activate the immune system.
I've also read that gluten, in all people--even those who are not gluten intolerant--plays a role in the amounts of zonulin secreted...in my mind, I imagine this to be something like how glucose stimulates our production of insulin...that gluten (and I guess other foods do it too, but gluten is the only one I've seen written in regard to zonulin production) causes the spikes in zonulin that could be responsible for a part of this cascade of health events. I've read that in the absence of gluten among people with autoimmune disorders, the leaky gut part might get better, and there may be hope for arresting or even reversving the disorder if other factors come into place right.
I would think one of the other factors needing to come into place would be withdrawal of casein and other dairy proteins, especially those from pasteurized cow's milk (and unpasteurized may be safer autoimmune-wise, but could cause deadly infectious diseases)...from what I've heard, milk from other animals...such as goats, has much less or in some types of goats no casein, although there would be other proteins that could still cause trouble in those sensitive to them.
As far as avoiding starches across the board...yes, there are studies. I can't remember the name of the bacterium now, but in many autoimmune diseases there is a specific bacterium to be found present...and I remember reading of one in particular associated with AS, although it isn't clear how that bacterium is involved...still, it's one that does feed on starches in general...from what I've read, studies are not entirely clear on that, but apparently some people find relief by avoiding all starches...so...there has been research involved in that.
After I discovered my problems with gluten, I became really curious about all of these sorts of things and started doing some reading...eventually runnning across an interesting, thought-provoking web site by a veterinarian, John Symes, in Mobile Alabama. Going by the name Dogtor J on the net...he writes of his similar problems with gluten sensitivity, and then sort of cross-referencing things in his veterinary studies/practice and did tons of research and came up with some interesting stuff... his site is interesting, for sure,
www.dogtorj.net even if you might not automatically agree with everything he says, still he puts out plenty for thought on there. In a nutshell...he has come to believe that there are four foods that can instigate leaky gut syndrome, which will then potentially go on to produce autoimmune diseases...the four foods are casein (anything at all dairy), gluten, soy, and corn. He points out that traditionally, these foods were included in people's diets only after some method of "digestion" outside of the body was engaged...such as fermentation, etc. He believes that simple-stomached animals, including dogs/cats and humans, simply cannot properly digest these foods.
Dogtor J really caught my attention when he said that he believed that celiacs who don't improve well after removing all gluten from their diets seem to get much better once they removed the other 3 potential offenders.
He also believes that he has seen evidence in his dogs/cats-patients, and people he's talked to, that other sensitivites that came about during the leaky gut episode may eventually become tolerated if the 4 foods above are completed avoided long enough.
So...that's all I know about it. I think some people we've seen here do make dramatic improvements in autoimmune disorders by going vegan, getting the casein out of their diets, but for others, I think some of the proteins in other foods may cause as much trouble. THe starches, if there is a particular bacterium involved that you're feeding with starches....then, of course, you would want to avoid that...maybe not forever, if everything else fell into place to set your body up for healing...but at least for a few years.
Just my opinion...for whatever it's worth.