I have a 17-year-old who is in Stage 2/early Stage 3 renal failure (CRF/CKD). She was diagnosed when she was 14, three years ago.
Let me start out by saying my vet made me try every prescription food out there. Most of the time I couldn't get my cat, Wintressia, to even TOUCH the stuff. It's all crappy food, full of by-products and grain fillers.
After a while of trying to force her to eat the prescription foods, plus dosing my cat with a mysterious product called Azodyl, we had Win re-tested. Her kidney values had gotten much worse.
I started to do some research of my own. I found Tanya's CRF site:
Tanya's Comprehensive Guide to Feline Chronic Kidney Disease - Everything You Need to Know to Help Your Cat
It's quite possibly THE best site out there for CRF kitty resources. She has a lot on there about foods.
The long and short of it is, vets get money for selling you the prescription foods. Whether Science Diet and Hills pay THEM to sell the food (notice how in a vet's office the walls are always lined with those foods?) or the vets get a commission/"reward" for selling the foods, basically the prescription foods exist for vets to push them onto pet owners with pretty much zero scientific research behind the diets. The vets make money from selling you Hills. They don't make money if you feed your cat Wellness or Natural Balance. Therefore, they push Hills or Royal Canin or Science Diet.
Most vets don't study animal nutrition. They don't really understand it. It's only recently that people are starting to become aware of the importance of animal nutrition. Long story short, those "prescription" diets are super low in protein. This is a HORRIBLE food to feed to an elderly, sick cat. A cat needs protein. It can't digest "brewers rice flour" and grains like that. A cat fed a low protein diet will actually start to waste away and will have muscle loss. Tanya goes into the debate here:
Tanya's Comprehensive Guide to Feline Chronic Kidney Disease - Nutritional Requirements of CKD Cats
It's my opinion, and my experience with my cat, that an elderly cat with renal failure needs to be given a normal high-protein diet, NOT a "prescription" low-protein diet. Dr. Pierson also goes into things here:
Feeding Your Cat: Know the Basics of Feline Nutrition :: healthy cat diet, making cat food, litter box, cat food, cat nutrition, cat urinary tract health
Basically, the TL;DR is two things: first of all, and MOST important, is no more dry food. None. No kibble. No snacks, no small meals of it, no bowl left out to "graze". Kibble is anathema to the kidney-failure cat. The kidney-failure cat needs as much moisture as possible in its diet in order to keep its failing kidneys in function. I'm not trying to be flippant - this is the first order of business no matter WHAT food you decide to feed your girl. It has to be wet food, preferably wet food mixed with water into "cat food soup". Dr. Pierson has some more on transitioning cats off of kibble here:
My cat was a lifelong kibble addict. I had no idea I was harming her kidneys by feeding her dry food. I felt horrible when the vet told me she only had 25% of her kidney function remaining. I knew it was my fault - I'd always just left a bowl of kibble for the cat to snack on whenever she wanted.
I was lucky though - my cat was incredibly easy to transition over to canned food, after the prescription food debacle/experiment was over. After that, I transitioned her to a raw diet. I'm a huge advocate of the raw diet - my cat's fur got thicker and softer, she started to have energy and run around and play again, and best of all, her BUN and creatinine values improved. She was actually getting BETTER on a moister diet.
Basically, my cat has been living for three fantastic years with "kidney failure", with me basically ignoring the vet insisting she had to be on some prescription food chock full of by-products and grains. I know I sound like a ranting lunatic, but I have my cat's bloodwork and urinalysis reports - I know I'm not losing my mind ;}
The REAL long and short of it is... feed your cat whatever she will eat
. It is better that she eats food, any food, even "crappy" food, than to have her go days without touching prescription food. Get her onto canned/wet only. Put out a lot more waterbowls/cups/places she can drink from. Consider a water fountain. Anything to get more moisture into her.
There is also a fantastic Yahoo mailing group for CRF kitties here:
There are wonderful people in the group who will be happy to answer any questions you might have, or to go over labwork with you.
I know this seems like a mountain of info, and I know you are probably scared, at least a little, with your kitty's diagnosis. But I know my cat is 17 with no sign of kicking the litterbucket any time soon, and I know other kitty owners have had cats live well into their 20s after being diagnosed with kidney failure. It's scary, but it's manageable.