I have Crohn's disease. More specifically, severe Crohn's disease.
Crohn's disease is one of a class of autoimmune diseases. The common theme for these diseases (including RA, Lupus, Colitis, MS, Psoriasis, etc.) is your body's immune system decides it's more fun attacking your own body than it is to attack outside infections.
Currently, there are no cures for Crohns or Colitis (a very closely related Inflammatory Bowel Disease). There is no diet, no lifestyle change, and no pill that can make those suffering from a Crohn's disease flare-up heal permanently.
There are a lot of drugs that can help. I should know, I've been on literally every one of them.
But for many people with IBD, the drugs stop helping (or never help in the first place), and your immune system goes thermonuclear on your guts. This happened to me last year.