Phosphorus deficiency isn't common in cats, however too much phosphorus can be a problem for cats with renal failure. Failing kidneys have a difficult time excreting enough phosphorus into the cat's urine; instead, the phosphorus accumulates in the cat's bloodstream, allowing the kidney disease to progress faster and making her feel sick. It's common for veterinarians to recommend feeding a cat in renal failure a low phosphorus diet.
If the vet has determined your cat would benefit from a low phosphorus diet, there are a number of prescription foods that will meet the requirement. Purina manufactures a kidney function food, available by prescription, with phosphorus levels of 0.18 percent for canned food and 0.3 percent for dry food. Hills Pet also offers a prescription kidney food, containing a 0.4 percent phosphorus level.
If you want to avoid prescription diets, you can look for food at your local pet store, but stick to cat food that has less than 0.5 percent phosphorus on a dry matter basis. Using a dry matter basis allows for a correct comparison between dry and wet food, taking into account the canned food's water content. Veterinarian Lisa M. Pierson of Catinfo.org compiled a comprehensive list of the phosphorus content of commercially available cat food, ranging from 0.57 percent to over 3 percent, depending on the brand, ingredient and preparation method, such as canned, freeze dried and dehydrated. Senior cat foods typically have lower protein and phosphorus levels, providing a good starting point in the search for a low phosphorus food.
To determine the dry matter basis of a nutrient, subtract the moisture content on the can's label from 100 to determine the percentage of dry matter, or % DM. Divide the nutrient by the % DM.
You may wish control your cat's phosphorus intake by cooking for her yourself. As obligate carnivores, cats have very specific nutritional needs, so you should consult a veterinarian or animal nutritionist to determine an appropriate homemade diet for your cat. According to veterinarian Ronald Hines of 2ndChance.info, cats don't tolerate low-protein diets well. However, high-protein foods, such as poultry and fish, also have naturally high levels of phosphorus. Cooked egg whites have the lowest amount of phosphorus per gram of protein than fish or meat, making them a viable source of protein with minimal phosphorus.
There is disagreement about the necessity to limit the amount of protein to feed a cat in renal failure. Feeding a high-quality protein -- one that has a high ability to be broken down into amino acids to be used by the body -- is important for a cat in renal failure. At 100, eggs have the highest biological value, followed by fish meal and milk, around 92 biological value.
The vet may provide a phosphorus binder to minimize the amount of phosphorus entering your cat's bloodstream. Calcium acetate and sevelamer are often used to block the absorption of phosphorus from food while still in the cat's digestive tract.