[pknight]

What was your diet like when you were taking them? It's been observed in some studies that delivered mixed results that responders had better diets (i.e. more bacteria friendly components in the diet such as indigestible carbs from vegetables/legumes/fruit etc) whereas non-responders had weaker diets in terms of providing the gut microbes nutrients.

[everybodyknows]

Diet is now generally low-FODMAP, emphasis on reducing fructose, glucose, and sugar alcohols e.g. sorbitol, erythritol, to which I seem especially sensitive -- this may be atypical among IBS patients.