Not IBD, but IBS-C for 6+ years intermittently. It had gone away for a long time (a few years) then returned WORSE than ever when I went paleo. Likely, it was a combination of stress and diet. I couldn't figure out why the healthier I ate, the worse it got until I realized that cutting out all the grains, starches, and sugars meant a giant increase in fiber, specifically all that insoluable fiber, which was really destroying my insides.
I was able to heal myself by going super low fiber (big reduction in veggies) and an increase in white rice and potatoes, probiotics, and some supplements like L-glutamine and bone broth.
Also realized that a trigger for my IBS is eating gigantic meals - my digestive system really can't cope with too much at once, even with the help of digestive enzymes and HCl. I had been intermittent fasting for months, hoping that by eating 1 huge meal per day, I'd give my digestive system downtime to heal whatever the problem was, but it turned out that IFing was actually making my problem worse. So, I went back to several smaller meals.
Basically, paleo/primal was one of the worse things to ever happen to me, digestively speaking, but I'm able to keep the parts of it that I think are most important (no gluten, dairy, soy, omega 6 crap oils, etc...) and not do the parts that wreak havoc on my system (huge+infrequent meals, fiber from veggies).