For example, I cannot tollerate corn bran. Don't know why, but small quantities of corn (I love corn ) destabilize me, although I tollerate other IF pretty well. I eat apples with their skins on for example.
I think it is normal to get more gas initially when you increase the IF. Especially if it was too sudden (e.g. a large increase rather than a SLOW gradual increase). You body just needs time to adjust to the new food. In particular, your bacteria need time to adjust to the new stuff you are feeding them. My husband used to have a lot of gas (he does not have IBS although I am beginning to doubt that, I think he just never complains) when he started eating much more IF because we wanted him to lose weight and lower his cholesterol level. Now that his body is used to the IF, he has much less gas.
I can't testify on my own, because I had to REDUCE the amount of IF I was eating rather than increase it when I first got IBS. When I switched to the BTC diet, there was almost no IF (but that in brown rice). Then I added some IF super slowly (only recently did I start to eat apples with the peel on) starting with oat bran. I didn't sense a notable increase of my gas.
I suggest you try to add less IF. And wait until your body adjusts to the new amount, then add a little bit more
While you are waiting and not getting enough IF to get on a regular BM schedule (I mean a normal BM, not one with super hard stools), use a gentle laxative such as Natural Calm/Magnesium Citrate. I wouldn't be able to survive and have such great progress had I not used that.
For the record, I am IBS-C, stable, thanks to Heather's diet