Quality digestive enzymes and probiotics with added prebitiotics are not only safe but beneficial for max. nutrient absorption.
Possible Side effects: Beautiful skin and hair.
Also for many IBS sufferers Gluten or Dairy can aggravate things so be absolutely sure these cause no problem (in which case you would actually have an intolerance or sensitivity)
I am Gluten sensitive, which can not be tested yet with standard testing, only by monitoring symptoms. I was given the IBS diagnosis long time ago and my problems worsened not avoiding Gluten until my reactions to Gluten became more and more obvious and my digestion was horrible. Cutting it out eventuallt resulted in a full recovery and no more digestive issues whatsoever. Since I am only "sensitive" the occasional cake won't kill me, but it is nothing I eat on a regular basis. Just an idea in case you haven't considered it.
https://chriskresser.com/is-gluten-sensitivity-real/