I developed a form of RA. There is about 1 to 3 percent or more of humans that have a sensitivity to foods in the nightshade family of foods. I was skeptical at first, but went on a restrictive diet excluding these foods for two weeks and got a big surprise. The inflammation and swelling went away. It is hard to avoid these foods and I find they are some of my favorites but if I want relief then I stay away from them. Some people can eat these foods with no apparent problems. You can check this information out here:
http://www.noarthritis.com/nightshades.htm