Have you ruled out psychological factors (which are probably more likely)? It's impossible to know for sure without doing a placebo controlled trial on yourself.
I have found that removing HFCS from my diet (basically, fizzy pop) and eating probiotic yogurt seems to mostly cure my mild IBS. I still get IBS due to stress, but don't seem to get it during non-stressful daily life any more. Of course, it still could be the placebo effect...it's hard to know for sure. It never affected my sleep though. The only time I would get anxiety would be due to an imminent bowel movement.
I have actually done extensive controlled tests on myself for a couple decades now. That is not to say I have all the facts. There are still many unknowns that I would like to eventually figure out, I just simply don't have the tools at my disposal and functional lab tests are time consuming.
I have found that removing HFCS from my diet (basically, fizzy pop) and eating probiotic yogurt seems to mostly cure my mild IBS. I still get IBS due to stress, but don't seem to get it during non-stressful daily life any more. Of course, it still could be the placebo effect...it's hard to know for sure. It never affected my sleep though. The only time I would get anxiety would be due to an imminent bowel movement.