I spent a few years in remission so here is my experience - obviously, others' experiences may vary, as we're all pretty different.
When flaring, I tend to lose weight, and when on steroids, I tend to gain weight. In remission, I was able to gain or lose like a normal person would. If I ate too much I gained, if I exercised and ate less I would lose. It was weird to be normal in such a way after so predictably gaining or losing due to disease and meds. I was able to exercise regularly and I got in pretty good shape - there were a few things I wasn't able to do, like jogging as it was too hard on my arthritic hip joints, and abdominal exercises would make my belly quite uncomfortable and it would also make my GERD act up, but as long as I avoided things like that, I could pretty much exercise as much as I wanted. I wouldn't say I ever felt 100% like my old self, but on some days I was a solid 90 or even 95%. I couldn't eat anything I wanted, I still had some trigger foods (and some foods would also trigger my GERD), so I still had to be careful about what I was eating. For the most part, though, as long as I took my meds and supplements and watched my stress level and didn't eat trigger foods - I was pretty darn normal and well. I still had a few bad belly days here and there, but I think that's true for normal people as well (like, eating something that doesn't agree with you, or getting a 24 hour tummy bug, etc). remission was wonderful - it didn't let me forget that I have a chronic illness, but it sure let me push that to the back of my mind much of the time. And the exercise kept the depression side of things well away, so I felt much happier in general. It was a really good time. I hope to get back there someday!