I second the EVO recommendation. The last vet I worked for (who was pretty traditional, but open to some “natural” ideas) actually started carrying it instead of the prescription high-protein foods for diabetic cats. It was the only non-prescription food she carried, but otherwise the closest place for clients to get it was 20 miles or so away a few suburbs over, and most of them just wouldn’t drive any further than the nearest Petco or Petsmart. We did actually see several diabetic cats go into remission as well (to be fair, we also saw it happen on the prescription diabetic foods, but they were both more expensive and contain some more questionable ingredients). I’m interested to hear that it helped your IBD cat, though, since the most frequent side effect we heard was that it caused nasty smelly diarrhea (and in fact it does this in one of my IBD cats too - of course it’s the fuzzy-bottomed one - ick!). The company told us that it usually only causes diarrhea when overfed, and this did seem to be somewhat true. But it reinforces the idea that you really need to feed mealtimes, not free-fed, and monitor the quantity. EVO’s canned food is great too (I never really worked out the price comparison to the dry, just decided to go with mostly canned because it never causes diarrhea in my cats). If you can’t find EVO, there’s one called Instinct (I think it’s by Nature’s Variety, can’t remember right now) that’s also high protein, no-grain, and Wellness makes one called “Core”. And Solid Gold makes “Indigo Moon”. I kind of rotate my cats through these as an occasional treat instead of their canned food. They love them all.) And I think there are a few others that are equally good, but harder to find. (You can get Wellness at Petco and Whole Foods, Solid Gold at Petco, and the others I’ve really only seen in pet specialty stores.) Be careful - all these companies make “normal” catfood too - it’s natural and probably higher quality than regular food, but still contains too many grains and too low a protein content, in my opinion. You have to read the labels to be sure what you’re getting.
If all you have near you is a Petsmart, Blue Buffalo Wilderness is another good choice. It’s comparable to the good foods Orpington posted.