Does my dog or cat with kidney disease really need a special diet?

Your pet has been diagnosed with kidney/renal disease. They aren't feeling well and maybe their appetite isn't what it used to be. Should you really spend the extra money and transition your pet to a diet prescribed for kidney disease by your veterinarian? The short answer is yes. Read below for the longer explanation of why:

Nutrition is arguably the most important aspect of chronic kidney disease management. By manipulating the composition of your pet's diet, we can slow the progression of disease and improve their quality of life. Renal diets have been shown to extend average survival time by over one year and lower the number of uremic crises in cats and triple the life expectancy of dogs with naturally occurring chronic kidney disease (CKD) (Elliott et al. 2000; Ross et al. 2006; Jacob et al. 2002).

The studies mentioned above evaluated diets that had several modifications including moderate protein restriction and phosphorus restriction. Therefore, it is difficult to determine which components of the diet are truly beneficial for CKD. The restriction of protein in the early stages of kidney disease is controversial and some argue dogs and cats with kidney disease should not be placed on a low protein diet in order to better retain muscle mass. Based on currently available research, the impact of protein restriction on early renal disease in dogs and cats is still unclear and some researchers find benefit while others find no change. However, once a patient is classified into the IRIS stage III/IV (http://iris-kidney.com) and has evidence of azotemia and uremia, high protein intake increases morbidity and azotemia while deficient protein intake correlates with morbidity and mortality (Polzin 1983). When assessing the protein content of a diet, it is important to remember that our bodies actually require amino acids, not protein. By feeding high quality protein sources with well-balanced ratios of essential amino acids, we can lower the overall protein content of the diet while preventing protein malnutrition. The levels of protein in prescription renal diets exceed the recommended amounts for dogs and cats set by the National Research Council.

While there is still much to be learned regarding the need and extent of protein restriction that is optimal for dogs and cats with CKD, the need for phosphorus restriction is less controversial. Studies have shown that by reducing phosphorus in the diet, we can reduce hyperphosphatemia and renal secondary hyperparathyroidism. Other nutrients to consider with renal disease are sodium, potassium, and omega-3 fatty acids. Sodium restriction has been recommended as a method to combat hypertension associated with CKD. However, studies demonstrating sodium reduction improves hypertension are lacking in dogs and cats. One study by Kirk et al. demonstrated high salt intake was associated with increased BUN, creatinine, and phosphorus in cats with varying levels of renal insufficiency. Dogs and cats with CKD can have either high or low concentrations of potassium in their blood and diets for renal disease vary in their potassium content. Diets high in omega-3 fatty acids in the form of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have been shown to improve kidney function (Brown et al. 1998).

Although there is still much to learn in regards to diet and the management of CKD in dogs and cats, it is clear that prescription renal diets extend lifespan and improve quality of life. Although most veterinarians know that renal diets are a critical part of managing CKD, several factors can limit their use. Although renal diets tend to taste really good, as renal failure progresses animal tend to have a reduced appetite. As an animal becomes more averse to eating, it may be necessary to try different brands or have a homemade diet formulated by a nutritionist. If a patient is unable to meet their energy requirements, a feeding tube may also be warranted. Homemade diets can also be used for clients opposed to feeding conventional pet foods or if a patient has multiple diseases that cannot be managed with a commercial renal diet (eg. dog with pancreatitis requiring low fat diet with CKD). Homemade diets can be used successfully for managing CKD in dogs and cats, but should be formulated by a board certified veterinary nutritionist.

References:

Brown, S.A., Brown, C.A., Crowell, W.A., et al. 1998 “Beneficial effects of chronic administration of dietary omega-3 polyunsaturated fatty acids in dogs with renal insufficiency.” J Labor Clin Med 131(5):447-455.

Elliott, D.A. “Nutritional Management of Kidney Disease.” Applied Veterinary Clinical Nutrition eds. Fascetti, A.J. and Delaney, S.J. Hoboken, NJ. Wiley-Blackwell. 2011: 251-260.

Elliott, D.A., Rawlings, J.M., Markwell, P.J., et al. 2000 “Survival of cats with naturally occurring chronic renal failure: Effect of dietary management.” J Small Anim Pract 41(6):235-242.

Kirk, C.A., Jewell, D.E., Lowry, S.R. 2006 “Effects of sodium chloride on selected parameters in cats.” Veterinary Therapeutics 7: 333-346.

Polzin, D.J., Osborne, C.A., Stevens, J.B., et al. 1983 “Influence of modified protein diets on the nutritional status of dogs with induced chronic renal failure.” Am J Vet Res 44(9):1694-1702.

Ross, S.J., Osborne, C.A., Kirk, C.A. et al. 2006 “Clinical evaluation of dietary modification for treatment of spontaneous chronic kidney disease in cats.” J Am Vet Med Assoc 229(6): 949-957