Carol wrote this book not knowing she was actually suffering from Ankylosing Spondylitis, though she does refer to the pains she had disappearing. It turns out that her diet is absolutely perfect for AS, as is explained by the web page (you really should read that too!). I have been following her diet now for 15 months, and my pain is completely gone. I know if I slip up on the diet though - the pain returns for a week or so.
If you have AS, do this diet. Don't cheat on it. You won't believe the difference it makes. Also, buy Elaine Gottschall's book, which contains a very similar diet, known as the Specific Carbohydrate Diet. "Breaking the Vicious Cycle : Intestinal Health Through Diet "
I don't know if this diet will help with all cases of IBS, however. It is possible that it will only help in cases of IBS which are related to one of the autoimmune conditions such as AS, Crohn's, Celiac, Ulcerative Colitis (although the diet is essentially the same, Elaine's book is targetted at the latter 3).
The recipes in this book and Elaine's book, combined, mean you never need to be bored with the food restrictions. There is plenty you can still eat, and food can still be interesting.
If you have Ankylosing Spondylitis, you MUST buy this book, and follow the diet strictly. You can be well! Allow at least a month before giving up, it can take a while to really notice the benefit. Note well what Carol says about sugar; don't try to cheat there either - it doesn't work (I tried).
Once you realise the strong association between starch and pain, you won't desire starchy foods again.