Cats & Dogs with Kidney problems

I need some input on kidney problems, today specifically for cat owners having to deal with them. I am getting confused by all the advise which is out there. I understand there are different opinions but it seems to me as if what I found so far just goes from one extreme to the other. Like protein intake if the animal suffers from the disease. Or, where is it coming from in the first place? Is it a result of feeding?