Every day a pet's body produces a number of waste toxins that must be removed from the body to prevent toxin build-up and illness. Most of these normal body toxins are circulated to the kidneys where they are filtered out of the bloodstream into the urine and then eliminated by a pet. A healthy kidney is capable of making highly concentrated urine so that a large amount of toxin can be excreted in a small amount of urine. When a kidney is diseased and begins to fail, it loses its ability to concentrate urine and more water is required to eliminate the same amount of toxin. Pets will begin to drink more and more to provide the failing kidneys with enough water. Eventually, a dog or cat cannot drink enough and toxin levels begin to rise. That is when obvious signs of kidney failure, such as lethargy, decreased appetite, weight loss and vomiting, become evident.
From this description it should be apparent that kidney disease occurs in stages and early kidney disease is vastly different from advanced kidney disease. The International Renal Interest Society (IRIS) has defined the following stages of chronic kidney disease.
Stages of Chronic Kidney Disease (CKD) based on Creatinine value
Table based on IRIS guidelines found at www.iris-kidney.com
|Product/Active Ingredient||At risk for kidney disease (based on breed risk, abnormal urine concentration, urine protein loss, increasing creatinine values, etc.)||Stage 1 CKD |
|Stage 2 CKD |
|Stage 3 CKD |
*no signs or mild signs
|Stage 4 CKD |
*moderate or severe signs
|Cat||< 1.6||< 1.6||1.6 - 2.8||2.9 - 5.0||> 5.0|
|Dog||< 1.4||< 1.4||1.4- 2.0||2.1 - 5.0||> 5.0|
The best diet depends on the stage of kidney disease present as one specific kidney diet does not fit all stages of kidney disease. For early stages of disease, prescription kidney diets may be too restricted and possibly lead to protein malnourishment and muscle loss. However, with advancing kidney failure, certain dietary modifications have been proven to help pets live significantly longer with less obvious signs of illness. It has never been proven which components of prescription kidney diets are most beneficial to pets, but an overall positive diet effect is seen as pets advance through the stages of kidney disease. It is important that you understand the nature and severity of your pet's kidney condition before selecting a suitable diet.
Characteristics of an ideal kidney diet for pets:
The ideal amount of protein to feed dogs and cats with kidney disease is a hotly debated topic and is controversial. Prescription kidney diets are formulated with 13-18% protein (on a dry matter basis) for dogs and 25-32% protein (on a dry matter basis) for cats. While evidence suggests restricting protein in the more advanced stages of kidney disease helps pets feel better, there is nothing to support protein restriction in early cases. In fact, protein restriction may lead to protein malnourishment and loss of muscle mass in pets with early kidney disease. This is especially common in cats who have much higher protein requirements than dogs.
Studies have failed to prove that restricting protein slows the progression of kidney disease in dogs and cats. Therefore, my recommendation is to continue feeding a high-quality, highly digestible protein source during the early stages of kidney disease (stage 1 and 2) when a pet has no outward signs and then restrict protein in the more advanced stages of kidney disease (stage 3 and 4).
As opposed to protein, decreased phosphorus intake has been proven to slow the progression of kidney disease and has been linked to improved length of survival in pets with kidney disease.
Based on current research information, pets with stage 3 or 4 kidney disease should eat foods with phosphorus levels between 0.2% and 0.5%. As the major source of phosphorus in the diet is protein, these levels can be achieved by decreasing protein intake with a specially formulated kidney diet or a balanced home-cooked diet. Pets with stage 2 kidney disease can also benefit from decreased phosphorus intake; however, many commercially available diets that are moderate in protein will contain a sufficiently low level of phosphorus and may be considered. Ask your veterinarian for more information on these diets.
While prescription diets do have a place in the treatment of pets with kidney disease, many high quality pet foods are likely to be acceptable in the earlier stages of kidney disease and may avoid detrimental states like protein malnourishment and muscle loss. Supplements, such as Omega-3 fatty acids , B-vitamins and antioxidants, can be added to a commercial diet to help support kidney health.