Phosphorus Can Be Key for Kidneys - Feline Nutrition

I have had two cats that have had kidney disease. As a result, I made it a priority to learn all I could about the nutritional needs of CKD cats. I learned a great deal and I feel that the best food they can be fed, is homemade.
You can make it from scratch, (using individual vitamins) or choose a premix for CKD cats.
The one I use is excellent. In part, here is what they say about their product:

“My vet sent home K/D food for my skinny old cat (with chronic kidney disease) to eat

“My vet sent home K/D food for my skinny old cat (with chronic kidney disease) to eat. I also have two young cats who find this food delicious and are getting fatter every day! What can I do to prevent the boys from becoming morbidly obese and still have the prescribed food around for Ladybug? I don’t want to keep the old girl locked up.”

Doesn't it have too much phosphorus

My vet put my cat on Hills Prescription Diet K/D cat food for kidney disease You may have heard that restricting protein is recommended for cats in kidney failure. Although this has been the “standard” treatment for decades, as far as cats are concerned, it has always been–and remains–very controversial. High protein/high phosphorus diets will not cause kidney disease in a normal cat, and restricted protein does not prevent kidney failure in a healthy cat. Some experts suggest that protein has no effect on the ultimate progression of renal disease. Research also shows that even very high protein diets do not make renal failure worse in cats (although high protein does worsen the disease in dogs and humans). (One pet food maker recently completed a study it claims shows that its restricted-protein diet increases lifespan in CKD cats. However, because the study has not been published, it is impossible to evaluate the data, which is contradicted by other research.) The real culprit is actually phosphorus, which meat contains in large amounts. The only practical way to restrict phosphorus is to restrict protein. Decreasing phosphorus intake (by restricting protein) can help some cats feel better, so it may be worth a try in a symptomatic cat. Adding a phosphate binder may also be needed.

NF Kidney Function™ Cat Food | Pro Plan Veterinary Diets

Baking soda should never be used in pet food! It is sodium bicarbonate and will spike the sodium levels in the food dangerously high. An Amazon review of the second edition of the book , points out this error all through the book of stating that baking soda is calcium carbonate. It is not! Also for cats with chronic kidney disease (CKD), the preferred phosphorous binder is aluminum hydroxide so as not to elevate their often already too high blood calcium levels. If the CKD is not too advanced and your cat's calcium a good level, well in the normal range, then calcium carbonate can be safely used. You can get calcium carbonate in bulk, likely through a pharmacy.

Kidney Disease in Cats | Little Big Cat