Its def worth trying to break the cycle - Holly would hold on for days on end till she literally exploded. Now she's got in the habit of going when she 'gets a poo feeling' and not holding on to it. She goes nearly every day now and they are easier for her to do.
We had to really work hard at getting her to go cos she was scared. we rewarded her, we encouraged her till the cows came home, we got cross when she held them in, we explained how it would be easier if she just did them. Eventually it worked, took about a year! My mum came up with the best tactic, if you ask Holly - do you need a poo? Do you want a poo? the answer is always no, But if you ask her Have you got a poo feeling in your bottom, she will always be truthful. Then we negotiate how we are going to get the feeling out, on the potty/toilet with or without mummy there (she does vbetter on her own) etc.
With my IBS its not really what I eat, its about non ignoring the signals when I need to go - Holly is the same.