Hi Christopher,
Very interesting post as I had similar problems and was told I had IBS , this was a year or two before I was diagnosed as a type 1 diabetic. Almost immediately after my diabetic diagnosis and my subsequent switch to a a very low car diet the problem ceased and It has not come back. I could not find any medical theories on the subject but now strongly believe it was caused by high Carb food i.e pasta, bread, rice , chocolate bars , chips etc. I try and keep my BS under (100 Mg/dl) 5.5 Mmol all the time and 98% of the time I achieve this.
I have been free of IBS for almost two years (one plus side of being diagnosed with diabetes) , I know how restrictive and embarrassing it can be:-(