There is no one food or group of foods to give up that will help all or even most people with arthritis. Some people report benefits from altering their diet, but it is very individual. You have to do a lot of detective work. Some people feel better when they give up animal protein.
Some people feel better when they give up all foods in the nightshade family.
The nightshade family also includes tobacco and belladonna. The nightshade family can be tricky. After eating a tomato, it can take as long as 48 hours before a reaction occurs. And it can actually take as long as six months for all reactions to stop. This means if you want to test for nightshades you may need to completely give up every member of this family for six months.