Great question Danny.... now just if we knew the answer!!!
As you said the western world's diet compared to the rest of the world is something that many look at for a proof that diet is cause of IBD. I believe it is called the SAD (Standard American Diet), which is said to be full of white flour and sugar (I am sure a search for this can bring up more on it, this is just from memory). I do not know the exact reasons that the medical community is not so positive on this idea, but it may be due to the differences that diet plays into each persons life and condition. Flairs are not triggered by the same foods for everyone, so this might be one of their reasons. This still does not explain how diet does not influence the start of the disease in some, but not others. Also, since family's typically eat the same food, the fact that not all families get the same disease may also be part of the reasoning why this is not true.
I have heard that a thought of how it is caused is some sort of bacteira gets inside the intestine (one that is not supposed to be there) and the immune system does what it is naturally supposed to do, which causes inflammation as the body literally is attacking itself. Which bacteria this is and how it happens or what causes this is still not explained (from what I have been told).
I have also heard their may be a genetic component to this, but it always seems that they say the answer to this must wait until the future when more research can be done.
