Cats with kidney disease are usually prescribed a low-phosphorus diet. This is because the kidney is no longer able to effectively remove excess phosphorus. While phosphorus is needed to grow bones and maintain body pH, excess phosphorus can weaken bones, cause muscle pain, and cause many other issues.
The Association of American Feed Control Officials (AAFCO) creates the nutritional guidelines for what is considered a “complete” diet for cats. Foods that do not have a minimum level of phosphorus must be labeled as “supplemental feeding only” or “prescription only.”
There is no maximum level of phosphorus in cat foods, so levels between brands and flavors vary significantly. Some brands are conscious of the fact that 60% of cats over the age of 10 have kidney disease, so they strive to keep phosphorus levels low. Other brands do not pay as close attention.
The most important nutrient in chronic kidney disease (CKD) is not phosphorus; it is, in fact, water. Cats don’t have a strong instinct to drink water. Even cats that drink “a lot” of water don’t drink nearly as much as they should.
Wet food is the best way to increase natural water consumption. Dry food should not be fed to cats with kidney disease, except when they absolutely refuse to eat anything else. Appetite is often an issue in kidney disease, so it may be difficult to convince all cats to switch to wet food. The most important thing for cats with kidney disease is to keep them eating and hydrated. Phosphorus is only a concern after these goals have been achieved.
Finally, the sources of protein should be considered. Protein is made up of amino acids, and cats’ bodies, like ours, need certain amounts of each amino acid to repair the body and build muscle.
Any amino acids not fed in the correct ratio are “burned” for energy. This process can be hard on the kidneys and should be avoided in cats with kidney disease. To prevent this, high quality meat proteins should be fed. Plant proteins, such as gluten or protein isolates, are unlikely to provide very many of the correct amino acids for cats, causing the kidneys to work harder.
