Whether you have RA or not, fasting regularly will first improve your health and if you are serious about it, it will finally free you from pain and suffering. Your bowel Sy may be an IBS, and a way your body is cleaning up toxicity or is sign of irritation. Fasting is safe for you, as long as you are careful and increase its duration by 24 hrs if the last fast was well tolerated. You need to read about proper breaking of fast and how to improve your diet overall. Curezone and this forum in particular have a wealth of info- on both. You may be undernourished with minerals and vitamins, but your weight is normal for your height. You eventually supplement when you finish your fast-breaking period. For your first 24 hrs fast you don't need special preparation. In the meanwhile read more about it and get somewhat prepared for the next one in a week or so.
BTW you need to be Gluten free for months, and avoid all exposure, if you have gluten intolerance, in order to calm down the immune reaction and completely reverse the damage and Sy with time.