I haven't seen diarrhea, just the one cat w/vomiting like clockwork a few hours after eating. The wet food goes, but I can't tell if they're both eating the same amount-- I've seen her eat a little and not been around enough to observe after it's first put down. They don't seem to drink much water. Her sister seems fine. Their owner had said she had some condition, just can't remember now or track down which vet. She sleeps a little more than the more active one not vomiting but doesn't seem listless. Their fur not horrible, not great.
In these cases - we then target the cause - the hypersensitivity to the food - changing their food to either a hydrolyzed protein diet or a novel protein diet.
Other common treatments for cats with IBD including medications such as metronidazole (an antibiotic) and even a steroid (prednisone)
Critical Care Veterinarian
Emergency and Critical Care Specialist