Have you been diagnosed with colitis or Crohn's? Wondering if you would get a better response on the IBS Diet boards instead of here.
Just my observation, white flour is not great, period. Don't think there is much difference in the nutritional value with white vs. "whole grain" flour. I get my fiber in "safe" fruits and veggies. I try to get my nutrition from protein (meat/fish/poultry) and veggies rather than grains (breads, pastas, etc.) I don't do well with all the starches/sugars. I am also yeast intolerant so I buy yeast-free millet bread, rather than wheat bread. You really need to experiment and see what works best for you. I did not have good results on the IBS diet, but others have found great success.
Have you eliminated all artificial sweeteners from your diet? Have you tried probiotics?