“Renal diets” have been considered to be “standard therapy” for managing cats with chronic kidney disease (CKD) for many years.1 These diets continue to be recommended by the IRIS Board for therapy of cats with IRIS CKD Stages 2– 4.2 However, recently some feline practitioners have begun recommending feeding diets containing higher levels of dietary protein; in some instances, clearly excessive levels of dietary protein. While the focus of recommendations proposed by feline practitioners is intended to specifically increase dietary protein intake, in reality, most, if not all, aspects of the “renal diet” have been altered because specific dietary modifications other than protein are not defined. As a consequence, a recommendation to feed “high(er?) protein diets” to cats with IRIS CKD Stages 2–4 fails to achieve many of the basic metabolic intentions on which the medical considerations of feline renal diets are formulated and recommended.3
There is evidence that poor nutrition may be associated with poorer outcomes in CKD.4 While some cats with CKD fed renal diets may become nutritionally depleted, it has not been confirmed that the protein content of these diets is consistently the mechanism underlying the nutritional depletion. Further, it has been shown that adequate nutrition can be sustained in cats fed renal diets.5 However, the ideal dietary protein content to provide to cats with CKD is unknown. Studies on the medical efficacy of renal diets in cats were performed using the protein content provided by the manufacturers, and the stated goals of these studies did not seek to determine the optimum protein content for these products. While small differences in the protein content exist among commercial products, studies directly comparing the efficacy of different commercial products have not been published.
While a consensus on whether renal diets contain the optimum protein content for cats with CKD has not been achieved, there is ample scientific evidence that excessive dietary protein content is potentially harmful in cats with CKD.6 Simply choosing to feed a cat with CKD a higher-protein diet is not the same as choosing a higher-protein “renal diet.” Although commonly called “low-protein” diets, feline renal diets are not actually low in protein and they do contain many other important modifications including reduced phosphorus and sodium content, increased B vitamins, potassium, and caloric density, added soluble fiber, a neutral effect on acid-base balance, and supplementation of omega-3 polyunsaturated fatty acids and antioxidants. As a consequence, feeding more protein potentially involves multiple errors in feeding cats with respect to phosphorus, potassium, sodium, fatty acids, antioxidants, fiber, and alkalinizing effect. While the evidence supporting these dietary components varies, it is generally accepted at least that phosphorus, fatty acids, antioxidants, and alkalinizing impact may influence progressive loss of kidney function.1,3