We talked a little bit about this in my nutrition class and yes, the general school of thought is to keep phosphorus down. So if you were wanting to homecook (which is totally cool and may be helpful for palatability, especially if the kitty goes off feed from not feeling well), I'd maybe go on the USDA's website and look up some of the meats that may be suitable based on their phosphorus level and then discuss it with a veterinary nutritionist (of which there are few). If I recall, lamb and chicken were not bad, but it's going to depend on the cut of meat too.
http://www.nal.usda.gov/fnic/foodcomp/search/
However, a couple of the companies differ on protein levels. High protein levels don't cause renal failure. I think I read on VIN (I wish I would have kept that link!) that in humans, even both vegans and non-vegans supposedly have equal rates of kidney failure. But if you
induce kidney failure, a low amount of protein is better than high levels and so most therapeutic diets have a low amount of protein in them. Another school of thought (I may be thinking of Royal Canin's?) says that very low protein is not good because it decreases glomerular filtration rate, so you need at least a modest amount. From my perspective as someone interested in holistic nutrition, I'd like to see a modest level of highly digestible and bioavailable protein sources used so as to not overwork or underwork the kidneys and use common sense with the ingredients. For instance, I'll pick on Purina.
Here is the ingredients of canned Purina NF (their veterinary kidney failure diet):
Water sufficient for processing, ground yellow corn, liver, beef, brewers rice, bacon fat preserved with BHA, canola oil, wheat flour, gum arabic, egg product, calcium carbonate, potassium citrate, salt, choline chloride, fish oil, vitamin supplements (E, B-12, D-3), niacin, calcium pantothenate, ferrous sulfate, riboflavin supplement, zinc oxide, biotin, manganese sulfate, pyridoxine hydrochloride, menadione sodium bisulfite complex, thiamine mononitrate, folic acid, copper sulfate, calcium iodate, sodium selenite.
Corn is not particularly digestable, yet it is the first ingredient besides water. Imagine a human patient with kidney failure. Would a human doctor recommend a diet with bacon fat (complete with a synthetic preservative that has known estrogenic activity) as the ingredient 5th on the list? Hmmm....I also really like fish oil as a supplement and it has been quite popular to add into many diets for many reasons (skin, heart, joints, etc) for the omega 3s. Which is all well and good, until one considers that fish, especially those at the top of their ocean food chain, bioaccumulate mercury, dioxins, PCBs, etc in their fat. Where does that oil come from? The fatty tissue in the fish. So if you wish to give fish oil, I would *highly* recommend paying slightly more and getting the molecularly distilled type so the kidney and liver are not so worried detoxing those nasties. It can be found at Sam's Club for less than $15 for a big bottle. JMHO.
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