There's also special feed that you can only get from vet. Friend had kitty with bad kidney issues, and put him on it, 3 years later he's thriving. It comes dry and canned and is a prescription food, and is a few $$$, but keeps their weight under control and heals the kidneys. Might want to ask about it, think it's Hills or Eukaneuba Prescription Kidney. You will want to keep kitty indoors as well if you decide to go this route, don't want him eating things out there that will disturb the balance. The theory is this food is low in protein and ash, so the kidneys can rest. You must be strict with the diet, no treats, no handouts of people food. He will cry and beg, but he will most likely get better. Good luck, hope your kitty gets better.