One disease that is not mentioned very often that we see in cats is chronic diarrhea. It is probably not talked about because, well, no one wants to talk about it. It is gross and cannot be described without describing very bad smells and accidents. I will leave the rest of that to your imagination and hope I have not grossed you out too much.
But the reason I want to talk about it is there are some things that can be done to help the condition. There are special diets available. The two I have seen have the most success are the Science Diet I/d and the Science Diet Gastrointestinal Biome.
Biome is a high-fiber dry cat food that has been shown to promote regular healthy stool and reduce the risk of diarrhea recurrence. It is made with ingredients that rapidly activate the gut microbiome and help manage the diarrhea. It contains a unique blend of prebiotic fibers, and it stimulates the microbiome to produce beneficial postbiotics.
I/d diet is highly digestible, and the nutrients are easily absorbed. It has prebiotic fiber, and is high in electrolytes and B vitamins that are known to help the lining of the gut. It also contains antioxidants, and Omega 3 and Omega 6 fatty acids.
If a cat is having chronic problems with diarrhea, especially if it is a kitten, I recommend starting with the Gastrointestinal Biome if possible. The next best choice would be the I/d. I have seen really good results with I/d, but the Biome is just a cut above.