Just back and Kbear has directed me to this thread!
DH says Mummyof3 has pretty much summed it up for you! Conveniently, nuts are something that he really must avoid! He needs to avoid any foods with small seeds in, like fresh tomatoes and even the seeds in cucumber. (just cut them out) Anything that doesn't digest well and could get stuck in the pockets that Mummyof3 describes. This is how DH was finally diagnosed, because something got caught in one of the pockets, went bad and caused an inflamation, which is diverticulitis.
Your dh needs to eat anything brown basically! And green too. Both have a lot of fibre in and will help to keep him regular! Fibrogel does work, also lactalose. Pretty disgusting to drink, I'm told, but DH used to mix it into a glass of juice or squash, so it was slightly more bearable.
TBH, DH was diagnosed so late, there was not much he could do. He ended up having to have the bad part of his colon removed, which thankfully has solved everything. An op is not always necessary though, so hopefully your DH can just control it though diet.
Shout if you have any other questions and DH and I will do our best to answer them.