Renal Diets: The Importance of Proper Nutrition and a Comparison of Available Diets by Jessica Fung and Kimberly Hsu

Introduction

        Chronic renal failure (CRF) is a problem in small animal practice, with 15-20% of all older dogs and cats exhibiting some degree of renal azotemia.⁴ The first goal is to identify the underlying cause of the renal disease, often this is not possible so treatment is directed at managing the complications of renal failure and maintaining quality of life.⁷ In dogs, CRF is progressive and irreversible, leading to uremia and death within months or years after the initial diagnosis. In contrast,  cats often have long periods of clinically stable renal function interspersed between episodes of progression.¹⁵ In addition to medical therapy, nutritional modification is one of the mainstays of treatment for chronic renal failure. Renal diets are formulated to modulate the metabolic disturbances and slow the self-perpetuating destruction of nephrons associated with CRF.

Key Nutritional Factors

Energy

        In general, the main theory is dogs and cats with CRF have similar energy requirements to healthy dogs and cats. As most renal diets are restricted in protein, adequate caloric density is achieved by increasing the amount of fat in the diet.⁸   Some proponents believe in a higher than  normal energy requirements for animals in renal failure.¹⁴

Protein

        While it has long been one of the cornerstones of diet therapy for CRF, protein restriction is controversial at best. The recommendation is  that dogs with CRF be fed a diet containing 14-15% DM of a high quality protein. Due to their higher protein requirements, it is thought that cats with CRF should consume diets containing 28-30% DM protein.⁸  Reducing consumption of non-essential amino acids theoretically results in decreased production of nitrogenous waste, reduced solute workload on the kidney, and improvement of clinical signs.¹¹

        Although protein restriction does seem to improve clinical signs in the uremic patient, its role on the progression of disease is not  clear, and research studying its effects is fraught with limitation. Despite evidence supporting the use of protein-restricted diets, the results of most studies have been confounded by concurrent alterations in energy and phosphorus levels.¹¹ There have also be conflicting results, with some researchers reporting that decreasing protein levels did not alleviated glomeruler hypertension, hypertrophy, hyperfiltration, or slow the progression of renal failure.⁸ Furthermore, as may studies have used the canine remnant kidney model for CRF, extrapolation of results to spontaneous CRF is sometimes difficult. Critiques of feline renal models claim that renal pathology cannot be effectively studied in patients with stable renal function.¹³

        While restricting protein intake may slow progression of renal dysfunction and ameliorate signs of renal failure, the major concern with limiting protein is protein malnutrition. Hypoalbuminemia, anemia, weight loss, and loss of lean body mass have all been associated with protein restricted renal diets. Moreover, a catabolic state may result from severe protein malnutrition, whereby the animal begins breaking down its own endogenous proteins. This may potentially trigger or aggravate a uremic crisis. Some believe that protein restriction only becomes necessary in profound renal failure. ⁸

Others  believe that adequate protein levels are crucial to maintaining GFR. Reproducible, randomized, clinical trials addressing solely the role of protein are needed before we can fully understand the role of dietary protein in CRF.

Fibre

        Like protein, the role in dietary fibre in CRF patients remains controversial. The theory is that fermentable fibre provides a source of carbohydrate for gastrointestinal bacteria, who utilize blood urea as a source of nitrogen for growth. As bacterial cell mass increases, fecal nitrogen excretion increases, and BUN decreases. The need for protein restriction is thus theoretically diminished.¹¹ The concern surrounding the “nitrogen trap” however is that unlike BUN, the classical medium uremia toxins are too large in molecular size to readily cross membranes, and are unlikely to be reduced by bacterial utilization.⁸

        As renal disease is thought to alter duodenojejunal and colonic transit times, another role for dietary fibre may be in improving gastrointestinal motility and health.⁸

Phosphorus(P)

        Phosphorus restriction is perhaps one of the only dietary measures has achieved widespread acceptance. While there is still no consensus on when phosphorus restriction should be initiated, evidence suggests P should be restricted prior to the onset of hyperphosphatemaia, as hyperparathyroidism usually occurs before serum phosphorus levels are detectably elevated. Early phosphorus restriction can help prevent renal secondary hyperparathyroidism, renal osteodystrophy, soft tissue calcification, and relative/absolute Vitamin D deficiency. A 1991 study in dogs with surgically reduced renal function showed that fed a low phosphorus diet (0.44% DM) had a 75% survival as compared to dogs fed a high phosphorus diet (1.44% DM) who had a 33% survival.¹¹ Similar studies in cats have demonstrated a reduction in renal pathology in cats fed a phosphorus-restricted diet.⁸ A1999 study in cats showed that diet therapy alone was effective at achieving euparathyroidism in 8/15 cats, with only 2 cats requiring oral phosphate binders. It is recommended that if normophosphatemia cannot be achieved within 2-4 weeks of restricting dietary phosphorus, intestinal phosphorus binders be added.¹³

Calcium

        As long as the Ca x P (mg/dL) product does not exceed 60, dietary calcium generally does not pose a problem, and there is little risk of soft tissue mineralization. Total blood calcium should be measured, however, and treatment tailored accordingly.¹¹ The Ca:P ratio in renal diets is usually 1:1 – 1.2:1.⁸

Sodium and Chloride

        Patients in renal failure can only vary their Na excretion over a limited range, so they cannot tolerate excessively low or high levels of Na intake. Excessive Na levels lead to hypertension, expansion of the ECF, fluid overload, and edema. Inadequate Na causes a decline in ECF, plasma volume, and GFR.⁸ Since a large number of CRF patients suffer from hypertension, and hypertension likely contributes to the progression of CRF, it is often recommended to provide normal to mildly restricted Na levels. Na is thought to contribute to intraglomerular pressure, which can exacerbate CRF. If modifying Na intake, it is important to do so gradually, as a rapid reduction in intake can lead to volume contraction and dehydration, which may potentially precipitate a uremic crisis.¹¹

        However, the role of Na restriction in alleviating hypertension is heavily debated. Altering the Na intake from 0.5 to 3.25 g / 1000 kcal did not influence the development of hypertension in dogs with surgically induced renal reduction, nor did it alter GFR. Interestingly, another study found that dietary NaCl intake had no effect on blood pressure in either clinically normal cats or those with surgically induced renal insufficiency. The decrease in Na intake was, however, accompanied by an inappropriate hypokalemic kaliuresis, a decrease in GFR, and activation of the rennin-angiotension-aldosterone system. These authors concluded by restricting NaCl, there was a risk of several potentially deleterious effects, without any clear beneficial effects on blood pressure.⁴

        It is also possible that the role of Na in producing hypertension is more complex than previously thought. A limited number of human studies have shown that blood pressure and blood volume are not elevated by high dietary Na intake with other anions. It was proposed that rennin is only released when there is an increase in renal intratubular Cl, and that Cl may act as a direct vasoconstrictor. The ideal Cl:Na ratio is thought to be 3:2. ⁸   Further complicating the issue, as in humans, our patients may likely also be classified as “sodium-responsive” and “sodium-unresponsive”. The role of sodium in causing oxidative stress and renal damage must also be further investigated.¹⁹

Potassium

        Patients with CRF, especially cats, are particularly prone to hypokalemia likely attributable to anorexia, decreased dietary intake, and urinary losses. Hyperkalemia is rarely documented. Most commercial diets are thus supplemented with K.¹¹

        Hypokalemia has been associated with both functional and morphological changes in the kidneys of dogs and cats. Hypokalemic animals tend to exhibit a reduced GFR and a decreased concentrating ability. However, it is not clear as to whether hypokalemia causes renal damage or is a consequence of it. It is possible that K depletion and kidney damage form a vicious cycle.¹³

Omega-3 and Omega-6 Fatty Acids

        Long chain n-3 fatty acids compete with arachidonic acid and moderate inflammation by altering eicosanoid, thromboxane, and leukotriene production. As such, long chain n-3 fatty acids are thought to improve renal hemodynamics by suppressing mediators of coagulation and inflammation. While studies on the exact dosing are lacking, long chain n-3 fatty acids have shown promise in the dietary treatment of CRF.¹¹

        A 1996 study showed that supplementation of long-chain n-3 fatty acids using menhaden fish oil for 20 months appeared to decrease inflammation, lower systemic blood pressure, alter plasma lipid concentrations, and preserve renal function. Although the mechanism remains unclear, it is hypothesized that the decreased levels of plasma cholesterol and triglycerides could be renoprotective. In contrast, supplementation of n-6 fatty acids (ie. safflower oil) is thought to be detrimental in dogs with CRF as consumption appeared to acutely increase GRF in a group of research animals, although the long-term effects of such changes have yet to be elucidated.¹¹

        The optimal ratio of n-6 to n-3 fatty acids in dogs with CRF is thought by many to be < 3:1. However, it is possible that the absolute concentrations of the fatty acids are more important. Without sufficient research, the exact doses and ratios remain to be determined. Furthermore, as cats are unable to elongate 18-C fatty acids, only fatty acids longer than 20-C are important in this species. The role of shorter chain n-3 fatty acids (i.e linseed oil) have yet to be determined in the dog. ¹¹

Acid Base Balance

        As renal function deteriorates, the kidney’s ability to excrete hydrogen ions and reabsorb bicarbonate declines, with a resultant metabolic acidosis. In response to the metabolic acidosis, renal ammoniagenesis increases which induces tubular inflammation and activation of complement, which likely contributes to the progression of CRF.¹¹

Cats in particular, may be unable to sufficiently increase the rate of renal ammoniagenesis, which may explain their increased predisposition to metabolic acidosis.¹³

Correction of metabolic acidosis is beneficial for numerous reasons. Firstly, it decreases anorexia, lethargy, and nausea. It also prevents that muscle catabolism associated with acidosis, thus aiding the adaptation a protein restricted diet. By correcting the acidosis, we also enhance the patient’s ability to deal with other acidosis-promoting stresses like diarrhea and dehydration. Finally, skeletal damage from bone buffering is limited, and cardiovascular function is improved.¹³ While protein restriction may help to reduce protein-derived acid precursors, supplementation with alkalinizing agents like potassium citrate and calcium carbonate may be necessary.¹¹ It is recommended that if plasma bicarbonate levels have not normalized within 2-4 weeks, further acid reduction and supplementation with alkalinizing agents be pursued.⁸

Vitamins

        While there is little research in veterinary medicine, oxidative damage is thought to play a key role in humans with CRF. As human CRF failure patients have shown decreased levels of Vitamins E and C, as well as increased markers of lipid peroxidation, supplementation of antioxidants may be of benefit. Children with focal glomerulosclerosis showed decreased proteinuria when given Vitamin E, and studies in rats have also suggested that Vitamin E supplementation may attenuate renal injury. Flavanols, polyphenolic antioxidants found in a variety of plants, also show promise. Flavanol supplementation in rats with CRF appeared to decrease glomerular capillary pressure by stimulating the production of nitrous oxide, thus relaxing smooth muscle fibres, and by inhibiting the release of angiotensin converting enzyme.¹¹

        As water soluble vitamins may be deficient in the polydipsic/polyuric patient, commercially available renal diets usually contain additional amounts of water soluble vitamins. While there is limited information available, pyridoxine, folate, thiamin, and niacin are often deficient in human CRF patients. Similarly, our veterinary CRF patients – especially those who are anorexic, vomiting, and polyuric – may also be at risk for B-vitamin deficiency.⁸

        Hypervitaminosis A has been reported in human CRF patients, likely due to decreased renal excretion. A 2003 study in canine CRF patients showed increased levels of Vitamin A. While information is lacking, it is wise to avoid excess consumption of Vitamin A.¹¹

        While control of hyperphosphatemia is usually sufficient, CRF patients are at risk for Vitamin D deficiency, due to decreased renal synthesis. Low dose Vitamin D can be administered in conjunction with a phosphorus-restricted diet.⁸

Effects of Dietary Therapy on Clinical Signs and Survival

        A 2000 study by Elliott et. al demonstrated that feeding Waltham Whiskas Low Protein diet controlled hyperphosphatemia and hyperparathyroidism associated with spontaneous CRF, and was associated with increased survival time.⁷ This study represents a breakthrough in that it was the first prospective dietary study testing cats with naturally occurring CRF, and stepped away from the feline kidney remnant model used previously. However, it is limited by the lack of randomization in its design. Cats refusing to consume the renal diet were continued on a variety of maintenance foods and formed the non-renal diet group used as a control. The use of intestinal phosphate binders further complicates the interpretation of results.

        In a double-blinded, randomized controlled clinical trial by Jacob et. al (2002), dogs with spontaneous Stage 3 and 4 CRF fed the Hill’s k/d diet had a 70% reduction in the relative risk of developing a uremic crisis, and remained free of uremic signs 2.5 times longer than dogs fed a maintenance diet. Their renal function also progressed more slowly, permitting them to live to a median lifespan of 594 days as opposed to the 188 days in their counterparts fed a maintenance diet. Owners feeding the renal diet reported higher quality of life scores than those feeding the maintenance diet¹⁰

A similar trial by Ross et. al (2006) showed that none of the Stage 2/3 CRF cats fed the Hill’s k/d diet suffered a uremic crisis within the 24-month testing window, while 26% of the control cats did. There was also a significant decrease in the number of renal-related deaths, with none of the renal diet group dying as opposed to 22% of the maintenance diet group.¹⁵

        The strengths of these two k/d clinical trials lay in the rigor of their experimental design, and the use of clinical patients.  Previous studies could not boast that they were double-blinded and controlled, and used surgical renal reduction to provide a model for CRF. They also enabled the study of a renal diet as it would be used in the clinic setting. However, as the Hill’s commercial diet was fed, it is impossible to tell whether the benefits of the diet were associated with the restricted protein, the restricted phosphorus or another ingredient. Hill’s is correct in arguing, however, that by studying a composite diet, the researcher can ensure that there are no adverse dietary interactions between ingredients. The example that Hill’s cites is a recent study where the addition of corn syrup interfered with the absorption of protein in a group of proteinuric animals, leading to protein malnutrition. While these weaknesses were recognized by the authors of the paper, the maintenance-fed group of cats had lower initial blood bicarbonate concentrations and higher SUN concentrations than the group of cats fed the renal diet. These differences suggest that the maintenance-fed group may have been more prone to developing uremic crises prior to the trial.

Evaluation of the Information Available to Veterinarians by Pet Food Companies

Hill’s

        The Hill’s website veterinary section was highly useful. Characteristics of the renal diet are clearly laid out and include an explanation for the rational behind each ingredient. Ingredient, average nutrients, caloric content, and daily intake recommendations were easily accessible. The indications and countraindications for the diet, as well as other diets to consider are of value to the practitioner. Summaries of published clinical trials were also available for this diet.

        For those practitioners seeking further information, the website contained a wealth of information in the form of Hill’s conference proceedings written by recognized experts in the field. These documents provided summaries on the latest research on fatty acids, antioxidants, sodium, protein restriction, and phosphorus restriction. These reports recognized the strengths and limitations of the current research on this topic, and even suggested areas of that required further investigation. Reports included the latest research in veterinary medicine (sometimes yet to be published), and often discussion of recent advances in human medicine as well. Bias is noticeable at times, as the Hill’s k/d diets remain the only formulas with double-blinded randomized clinical trials.

        The client is provided with almost the same amount of detailed information as the veterinarian.

Purina

        The Purina Veterinary Diets website was comparable to that of Hill’s. Detailed information on each diet was available, including average nutrient levels. Detailed research reports were also available summarizing current research on topics pertaining to renal diets, such as sodium, omega fatty acids, etc. A useful client brochure outlining the pathophysiology of renal failure, concurrent medical treatment, and key nutritioonal features of the NF diet is available to the practitioner. While there is no discussion of how this information actually pertains to the Purina NF diet, one can assume that the company’s philosophy is likely aligned with the research they provide.

        The client section of the PVD website summarizes the key nutritional features, and provides basic label information.

Medical/Royal-Canin

        Interestingly, this is the only company where the information provided to the client is essentially the same as that presented to the veterinarian. Detailed explanation of the rational behind the renal diet is provided to client, who has access to everything except for a detailed nutrient analysis.

        A series of technical reports is provided to the veterinarian, and contain useful information on product specific use. For example, the company recommends that small/medium dogs in renal insufficiency be fed a Weight Control/Mature formulate, unless proteinuric or progressively azotemic, in which case the LP diet should be used. Large breed dogs, however, are to be started on the MP diet. This information, while enormously valuable, is not provided in the description of the renal diets, and is difficult to find. No information pertaining to research on renal diets is provided.

Iams/Eukanuba

        Separate technical reports outlining the roles of dietary phosphorus, protein, fatty acids, and potassium make understanding dietary modifications easy for the veterinarian. References are available for further reading. Typical or average analyses are difficult to access. Ample information is available to the client explaining rational and nutrient content.

Summary of information provided by the pet food company

        Although they differ slightly in philosophy, it appears that current renal diets are all influenced by the same body of research. With the exception of Medical, all of the companies present this research to the veterinarian in the form of company-sponsored summaries. What is sorely lacking, however, is an effort to specifically relate the research to the actual formulation of the diets. When questioned, most pet food representatives could not adequately their company’s decision to use certain levels of nutrients, citing “proprietary” information in a number of cases. Information on key ingredients like omega-3 fatty acids was frequently unavailable, so claims were hard to evaluate. Lack of a standard presentation made diet comparison difficult at times.

As Hill’s is the only company with a properly controlled clinical trial, the need exists for validation of other renal diets. Many researchers of renal diets, it seems, have close ties with Hill’s. The lack of consensus on the appropriate levels of key nutrients (protein, sodium, phosphorus, etc.) warrants further research about the individual components of renal diets.

        Better guidelines on when dietary modification should be instituted in the management of renal patients are also needed. Use of a standardized system like the IRIS staging system in making recommendations would be of benefit. As current studies have focused on patients in the later stages of renal failure, controlled clinical trials for animals in the earlier stages of this disease are needed. Long-term studies are needed, especially in cats, where renal function is stable when therapy is initiated.

       

Company Philosophies Towards Canine Renal Diet

There is no such thing as the ideal renal diet because there are still so many controversies to sort out.  The one thing all companies can agree on is phosphorus restriction and omega 3 and 6 supplementation.  They also have some degree of protein restriction although they vary in how little they put in.  With the exception of Eukanuba, they also restrict sodium in an attempt to prevent systemic hypertension; Eukanuba’s sodium levels are actually quite high and we suspect it is related to their claim of palatability. 

Some differences in the companies’ philosophies is that Hills does not believe in potassium supplementation which may be the right stance because dogs do not commonly go hypokalemic with chronic renal failure.  Medi-cal and Eukanuba are the only ones promoting a fibre system but where Medi-cal says it is to promote digestive tract health, Eukanuba calls it a “nitrogen trap fibre system”.  Eukanuba and Royal Canin are also unique in that they have two formulations.  Where Eukanuba has an “Early Stage” and an “Advanced Stage” formulation,  Royal Canin has a “Moderate Protein” for large breed dogs and a “Low Protein” for small to medium breed dogs.  Another unique feature is that Royal Canin and Medi‑cal recommends a small to medium breed dog and all cats with renal insufficiency be fed Weight Control or Mature until they develop severe proteinuria – at that point you can switch them over to the renal formulation.  Hills, Medi-cal and Royal Canin are also the only companies that say they supplement water soluble vitamins and antioxidants

Comparison of the (abbreviated) typical analyses of the different canine dry kibbles

Table 1.1:  Comparison of the (abbreviated) typical analyses of the different canine dry kibbles

	NRC Maintenance Requirement g/d	Eukanuba: Early Stage	Eukanuba: Advanced Stage	Hills: k/d	Purina: NF	Medi-Cal: Reduced Protein	Royal Canin: Renal MP	Royal Canin: Renal LP
Crude Protein	50.00	47.21	33.80	36.82	36.20	34.20	39.00	32.90
Crude Fiber	10.00	5.63	4.14	2.74	2.06	5.57	4.02	9.72
Phosphorus	0.65	0.99	0.56	0.55	0.65	0.86	1.01	0.76
Potassium	1.30	1.57	1.26	0.92	1.96	2.25	2.24	2.34
Sodium	0.17	1.19	1.05	0.47	0.50	0.28	0.63	0.53
Chloride	0.24	2.74	2.55		1.31
Omega 3 FA	1.38	6.34	6.13		0.68
Omega 6 FA	0.02				6.31
Omega 6 : 3	3 : 1	5 : 1			9.4 : 1

What is most interesting to note from this table, is that while every company touts omega 3 and 6 supplementation, Purina is the only one that tells us exactly how much was added; but even then their ratio is below ideal. Eukanuba: Early Stage does give a ratio but does not give the exact amounts.

All companies have restricted proteins when compared to NRC maintenance requirements but as you would expect, the Eukanuba: Early Stage and Royal Canin: Renal MP have the highest protein levels.  Since Royal Canin: Renal MP is designed for large breed dogs in chronic renal failure, it has lower protein levels than the Eukanuba: Early Stage.  The remainder of the diets are pretty similar in protein content with an average of 34.8g/1000 kcal.  What is interesting to note is that Eukanuba and Medi-cal promote their soluble fibre but their crude fibre content is not as high as the Royal Canin: Renal LP.

All five diets say they restrict the phosphorus but Eukanuba: Advanced Stage and Hills are the only ones below the NRC Maintenance Requirements and Purina is right on the cusp; every other diet is in excess.  Eukanuba: Early Stage and Royal Canin: Renal MP have the highest phosphorus level which is expected since they have the highest protein levels and it is difficult to decrease phosphorus unless you decrease protein.

Even though dogs do not usually get hypokalemic with chronic renal failure, most diets supplement potassium.  Many argue it is in the form of a buffer so it is functioning to fix the metabolic acidosis as opposed to preventing the hypokalemia, but some just put it in specifically for the hypokalemia.  As expected, because they do not supplement potassium, Hills has the lowest potassium levels.

With the exception of Eukanuba, all diets say they are sodium restricted.  While they are not as elevated as Eukanuba, all diets are in excess of the NRC Maintenance Requirements. What would have been interesting to assess is the chloride levels in the different diets.  If it truly is elevated intrarenal chloride levels that allows hypernatremia to stimulate the renin-angiotension-aldosterone system, than the ratio between chloride and sodium would be more important than the absolute amount of sodium.

Comparison of the (abbreviated) typical analyses of the different canine canned diets

Table 1.2: Comparison of the (abbreviated) typical analyses of the different canine canned diets

	NRC Maintenance g/d	Eukanuba: Early Stage	Eukanuba: Advanced Stage	Hills: k/d	Purina: NF	Medi-Cal: Reduced Protein	Royal Canin: Renal MP	Royal Canin: Renal LP
Crude Protein	50.00	No Canned Diets	No Canned Diets	32.28	35.51	41.80	45.30	34.97
Crude Fiber	10.00			0.87	3.69	1.30	3.10	4.10
Phosphorus	0.65			0.48	0.64	0.70	0.60	0.64
Potassium	1.30			0.81	1.56	2.00	2.30	2.10
Sodium	0.17			0.41	0.50	0.80	0.80	0.58
Chloride	0.24				0.92
Omega 3 FA	1.38			4.21	1.28
Omega 6 FA	0.02				8.81
Omega 6 : 3	3 : 1				6.9:1

Once again, while all their packages say they have added omega 3 and 6 to their diets, Purina is the only one that tells us exactly how much was added but like the dry kibble, the ratio is still too low.

The caloric distribution of the canned feeds is very similar to the dry kibble with Royal Canin: Renal MP being the highest and the rest being quite similar to one another.  Medi-cal’s canned diet is actually a bit higher in protein than its dry kibble.  What is more apparent in the canned diets is that the fat content is much higher to compensate for the low protein levels.

The canned diets have a very similar nutrient breakdown as the dry kibble but they are better for phosphorus and sodium restriction. It is apparent that Hills does not supplement potassium as it has the lowest amount. 

Comparison of the primary ingredients used in the different canine dry kibbles

Table 2.1:  List of the primary ingredients used in the different canine dry kibbles

Eukanuba : Early	Eukanuba : Advance	Hills	Purina	Medi-Cal	Royal Canin : MP	Royal Canin : LP
Corn meal	Corn grits	Brewer’s rice	Whole grain corn	Corn	Rice	Rice
Corn grits	Chicken fat	Pork fat	Brewers rice	Oat flour	Corn	Brown rice
Chicken	Soy protein isolate	Dried egg product	Dried egg product	Rice	Brown rice	Corn
Brewers rice	Dried beet pulp (sugar removed)	Flaxseed	Animal fat	Chicken fat	Chicken meal	Chicken fat
Dried beet pulp (sugar removed)	Natural chicken flavour	Corn gluten meal	Sugar	Dried egg powder	Chicken fat	Natural flavour
Soy protein isolate	Gum arabic	Chicken liver flavour	Dried whey	Dried beet pulp	Wheat	Powdered cellulose
Fish meal	Fructo-oligosaccharides	Powdered cellulose	Sodium caseinate	Herring meal	Natural flavour	Chicken meal
Chicken fat	Calcium carbonate	Calcium carbonate	Animal digest	Dried brewer’s yeast	Dried egg powder	Corn gluten meal
Dried egg product	Fish oils	Dried beet pulp	Calcium carbonate	Natural flavour	Fish oil	Fish oil
Natural chicken flavour	Corn gluten meal	L-lysine	Vegetable oil	Flax meal	Potassium chloride	Wheat gluten

Table 2.2:  Comparison of the primary ingredients used in the different canine dry kibbles

	Eukanuba: Early Stage	Eukanuba: Advanced Stage	Hills: k/d	Purina: NF	Medi-Cal: Reduced Protein	Royal Canin: Renal MP	Royal Canin: Renal LP
Carbohydrate	Corn Brewer’s rice	Corn	Brewer’s rice, corn gluten meal	Whole grain, brewer’s rice, dried whey	Corn, oat, rice	Rice, corn, wheat	Rice, corn, wheat gluten
Protein	Chicken,  soybean protein isolate, fish meal, dried egg product	Soybean protein isolate	Dried egg product	Dried egg product	Dried egg, herring meal	Chicken meal, dried egg product	Chicken meal
Soluble Fibre	Dried beet pulp	Dried beet pulp, gum arabic and fructooligosaccharides	Dried beet pulp		Dried beet pulp
Fat	Chicken fat	Chicken fat, fish oil	Pork fat	Animal fat, vegetable oil	Chicken fat	Chicken fat, Fish oil	Chicken fat, Fish oil
Omega 3 & 6 sources	Fish meal	Fish oil	Flaxseed		Herring meal, flaxmeal	Fish oil	Fish oil
Buffers		Calcium carbonate	Calcium carbonate	Calcium carbonate		Potassium chloride

What is interesting to note is the similarities between the different diets.  In regards to the carbohydrates source, all diets use corn or rice primarily.  Corn has its benefits for renal diets because it has an average level of proteins (as opposed to elevated like with barley or rice bran) and is a good source of linoleic acid.  Rice and brewers rice is also a good choice because it is low in phosphorus (as opposed to barley or rice bran again).  Royal Canin is the only one who has some wheat gluten but because wheat is higher in protein than the corn or rice, Royal Canin can use less of its other protein sources. 

Their choice of primary protein sources are quite similar too: chicken (fresh or meal), soybean protein isolate, fish meal and dried egg product.  Even though Eukanuba and Medi-cal are the only ones who promote their fibre content, Hills has dried beet pulp in its primary ingredients too.  Eukanuba and Royal Canin use fish meal/oil to supplement omega 3 and 6, but Hills uses flaxseed.  Medi-cal uses both herring meal and flaxmeal.   With the exception of Eukanuba: Early Stage, Medi-cal and Royal Canin: Renal LP, they all have some form of buffer in their primary ingredients list.

Comparison of the primary ingredients used in the different canine dry kibbles

Table 2.3:  List of the primary ingredients used in the different canine canned feeds (minus water are the first ingredients)

Hills	Purina	Medi-Cal	Royal Canin : MP	Royal Canin : LP
Egg white	Ground yellow corn	Pork by-products	Pork by-product	Pork by-product
Corn Starch	Liver	Rice flour	Chicken by-product	Brewer’s rice
Pork liver	Beef	Pork liver	Brewer’s rice	Chicken by-product
Chicken Fat	Rice	Corn meal	Vegetable oil	Vegetable oil
Sucrose	Animal fat	Chicken fat	Fish oil	Fish oil
Flaxseed	Canola oil	Brown rice	Calcium carbonate	Powdered cellulose
Dried whey	Guar gum	Chicken	Dried beet pulp	Calcium carbonate
Chicken liver flavour	Dried egg product	Salmon	Potassium citrate	Potassium citrate
Calcium carbonate	Calcium carbonate	Dried Egg	Powdered cellulose	Cassia gum
Fish oil	Gum arabic	Calcium carbonate	Cassia Gum	Dried egg

Table 2.4:  Comparison of the primary ingredients used in the different canine canned feeds (minus water are the first ingredients)

	Hills: k/d	Purina: NF	Medi-Cal: Reduced Protein	Royal Canin: Renal MP	Royal Canin: Renal LP
Carbohydrate	Corn, dried whey	Corn, rice	Rice, corn	Brewer’s rice	Brewer’s rice
Protein	Egg white, pork liver	Liver, beef, dried egg product	Pork byproduct, pork liver, chicken salmon, dried egg	Pork byproduct, chicken byproduct	Pork byproduct, chicken byproduct, dried egg
Soluble Fibre		Gum arabic		Dried beet pulp
Fat	Chicken fat, fish oil	Animal fat, canola oil	Chicken fat	Vegetable oil, fish oil	Vegetable oil, fish oil
Omega 3 & 6 sources	Flaxseed, fish oil	Canola oil	Salmon	Fish oil	Fish oil
Buffer	Calcium carbonate	Calcium carbonate	Calcium carbonate	Calcium carbonate, potassium citrate	Calcium carbonate, potassium citrate

The primary ingredients list for the canned diets is very similar to the dry kibble.  Once again, corn and rice are the common grains used for carbohydrate sources and most diets have fish oil, flaxseed as an omega 3 and 6 fatty acid supplement.  All products have a buffer.  What is different is the source of protein which includes a lot more liver and by product  but this is likely related to the fact that meals are dry and may be difficult to put into canned feed.  Unfortunately, because of the high water content of canned diets, most are are lacking a soluble fibre source in their primary ingredients list – Purina and Royal Canin: Renal MP are the only ones with some form of soluble fibre (which is interesting since Medi-cal promotoes their fibre on the packaging). 

Best diet

Given the the contradicting research and lack of comparable scientific literature about the various diets, it is difficult to determine which diet is “best”.  Eukanuba and Royal Canin are nice because you can better customize the diet to your patient.  Unfortunately, the listed omega 6:3 ratio from Eukanuba is lower than the ideal 3:1; it would be unfair to hold this ratio against Eukanuba because the only other diet that even offers this information is Purina who is worse (9.4:1).  If you believe the theory that elevated intrarenal chloride levels is a more important contributing factor to systemic hypertension than absolute sodium levels, Eukanuba may be problematic because it has a very high chloride: sodium ratio.

Hills, Purina and Medi-cal are basically equivalent in terms of crude protein, crude fibre, and sodium levels.  A potential problem with Hills is that it is deficient in potassium.  While some Internists argue that it’s better this way (as it is easier to supplement potassium than eliminate) but if the dog develops hypokalemia, the diet would not correct it.  Medi-cal is not as phosphorus restricted as Hills and Purina.  Similar to the Eukanuba diets, if you are worried about the sodium-chloride association with hypertension, Purina may be a concern too because its chloride:sodium ratio is quite high.  However it would be unfair to say these two are the only ones with elevated chloride because the others did not test for chloride so we do not know their levels. 

Even though there are some minor differences between the diets, with our limited understanding of the ideal renal diet, any of these diets would be good for a renal patient.  Palatability may be an issue for some dogs so finding one that the patient likes may be as important as the nutritional composition of each diet.  Another important point to bring up with the clients is the fact that the recommended feeding guide from the companies may be underfeeding the dogs so be wary if they start losing weight.  Especially now that we are restricting proteins, it may be prudent to calculate each patient’s daily energy requirement and make custom feeding guide for each patient.  In general, the dry and canned forms are similar in composition but the increased moisture content and increase palatability makes the canned form invaluable in some cases.

Table 3:  Cost comparison for an active 10-kg dog based on daily energy requirement and prices at the Western College of Veterinary Medicine: Veterinary Teaching Hospital 

	Eukanuba: Early Stage (aka: Iam’s Renal?)	Eukanuba: Advanced Stage (aka: Eukanuba Kidney?)	Hills: k/d	Purina: NF	Medi-Cal: Reduced Protein	Royal Canin: Renal MP	Royal Canin: Renal LP
Dry Kibble	N/A	N/A	$1.22	$1.24	$1.33	$1.29	$1.27
Canned Feed	N/A	N/A	$6.63	$4.13	$5.30	$4.39	$4.07

A cost comparison of the diets was performed for a 10kg dog and it was determined that the dry kibbles were all about equivalent but the Hills canned diet is the most expensive.

Can non-renal diets be used

Not all clients wish to purchase prescription diets so two non-renal, over the counter diets were examined – Science Diet: Mature Active Longevity and Science Diet: Light Adult.  The reason for chosing a senior diet is because most dogs with chronic renal failures develop the disease later in life and thus a seniors diet is the most suitable diet.  As for the weight loss diet, they are supposed to be protein and fat restricted already and high in fibre so it could be beneficial for chronic renal failure patients too.  In addition to the two over the counter diets, the Medi-cal vegetarian diet was examined because of the research being done into the use of vegetable proteins in humans.  Because of the variability between the diets, the three non-renal diets could not be compared to an average of the 7 renal diets, so instead they were all compared to the Hills: k/d. 

Table 4.1:  Comparison of renal and non-renal canine diets; dry kibble

	NRC Maintenance Requirement	Hills: k/d	Science Diet: Mature Adult Active Longevity	Science Diet: Light Adult	Medi-cal: Vegetarian
Crude Protein	50.00	36.82	48.43	75.62	51.00
Crude Fiber	10.00	2.74	10.54	45.06	8.00
Phosphorus	0.65	0.55	1.46	1.79	1.46
Potassium	1.30	0.92	2.08	2.31	2.12
Sodium	0.17	0.47	0.45	0.71	0.85
Chloride	0.24
Omega 3 FA	1.38
Omega 6 FA	0.02
Omega 6 : 3	3 : 1

As can be seen from Figure 3.1, Hills: k/d is more protein restricted than the non-renal diets.  While the Science Diet: Mature is slighly below NRC Maintenance Requirements and the Medi-cal: Vegetarian is slightly above, the Science Diet: Light has quite a bit more protein than the others.  To make up for the low protein, Hills: k/d has a lot more fat than the other diets. 

The calcium and sodium content of the four diets is quite close but the phosphorus is too high in the non-renal diets; when averaged together, they are nearly 3x as great as the Hills: k/d.  The potassium level is also much higher in the non-renal diets but that may not be an issue in certain chronic renal failure dogs. 

Table 4.2:  Comparison of renal and non-renal canine diets; canned feed

	NRC Maintenance	Hills: k/d	Science Diet: Mature Adult Active Longevity	Science Diet: Light Adult	Medi-cal: Vegetarian
Crude Protein	50.00	32.28	52.91	60.50	70.00
Crude Fiber	10.00	0.87	4.60	30.09	7.00
Phosphorus	0.65	0.48	1.64	1.58	2.40
Potassium	1.30	0.81	2.01	2.05	1.85
Sodium	0.17	0.41	0.46	0.96	2.00
Chloride	0.24
Omega 3 FA	1.38	4.21
Omega 6 FA	0.02
Omega 6 : 3	3 : 1

The total crude protein and carbohydrate levels are lower in the canned products than the dry kibble but otherwise the trends are similar to the dry kibble.

The calcium, phosphorus and sodium levels are also higher in the Medi-cal:Vegetarian canned food as compared to the dry kibble but the other values are quite similar to the dry kibble diets.

When all the data is taken into consideration, it is unlikely that non-renal diets can be used.  The only thing researchers can agree on is that phosphorus should be restricted and all three diets have elevated phosphorus levels.  While the degree of protein reduction is still controversial, all three diets are at or above the NRC Maintenance Requirements so it is likely too high for a chronic renal failure patient.

If an owner insists on using a non-prescription diet, a senior diet is likely best because it has the lowest protein levels, has supplement potassium and low sodium.  Just know that the owner will likely have to supplement the diet with an oral phosphate binder.

Company Philosophies Towards Feline Renal Diets

In regards to the companies’ philosophies towards their feline diets, they are very much similar to their philosophies towards their K9 diets.  Once again, they have restricted their protein, phosphorus and sodium (except for Eukanuba) and all companies have supplemented potassium (including Hills), and omega 3 and 6 fatty acids.  Similar to what they did with their canine diets, Medi‑cal and Eukanuba promote the use of fibre in their diets but where Medi-cal uses it to “maintain digestive tract health”, Eukanuba uses a “nitrogen trap fibre system” – both products use dried beet pulp but Eukanuba also has gum arabic and fructooligosaccarides as soluble fibre.  Hills, Medi-cal and Royal Canin still supplement water soluble vitamins and antioxidants into their feline diets, but now Purina has also added water soluble vitamins to theirs.

Comparison of the (abbreviated) typical analyses of the different feline dry kibbles

Table 5.1:  Comparison of the (abbreviated) typical analyses of the different feline dry kibbles

Nutrient (g/1000 kcal)	Natural Prey Diet	Eukanuba: Multi-Stage	Hills: k/d	Purina: NF	Medi-cal: Reduced Protein	Royal Canin: Renal LP
Crude Protein	151.00	63.64	67.68	72.41	60.80	61.90
Crude Fiber	4.50	4.66	4.23	2.90	2.81	9.80
Phosphorus	5.00	1.14	1.08	0.97	1.29	0.80
Potassium	2.00	1.48	1.76	2.06	2.11	2.20
Sodium	1.00	1.02	0.56	0.46	0.70	0.70
Chloride		1.64		1.50
Omega 3 FA			0.33	0.74
Omega 6 FA		9.86		4.75
Omega 6 : 3	3 : 1			6.5 : 1

What is most interesting to note from this table, is that while every company touts omega 3 and 6 supplementation, Purina is the only one that tells us exactly how much was added; but even then their ratio is below ideal.

All companies have restricted crude protein levels as compared to the natural prey diet.  While there is some variation, the average crude protein content is 62.29 g/1000 kcal.  What may be interesting to note is that Purina has a higher crude protein level than either Eukanuba or Medi-cal, even though the latter two promote their fibre systems.  As to the crude fat and crude fibre, there is some between the diets but as a whole they are quite similar to one another. 

All five diets restrict calcium to the same degree but the reasoning behind this is unclear.  Hypocalcemia is already a risk when cats undergo hyperphosphatemia spikes so further restriction of this may pose issues in the long run.  A potential explanation may be that the natural prey diet includes a lot more bones than a cat may choose to eat if he caught the prey himself, so perhaps the elevated levels in the natural prey diet is a bias instead of a true elevation.  But further studies into was a cat would “normally” eat and what a cat’s true nutritional requirements are would be needed to determine if this is the case. 

All five diets restrict the phosphorus to about the same degree and with the exception of Eukanuba, has restrict their sodium as well.  Eukanuba makes not claims to do such a thing and instead promotes the palatability of their product so we suspect the elevated sodium levels are contributing to the palatability.  What would have been interesting to assess is the chloride levels in the different diets.  If it truly is elevated intrarenal chloride levels that allows hypernatremia to stimulate the renin-angiotension-aldosterone system, than the ratio between chloride and sodium would be more important than their absolute amounts. 

Cats are more prone to hyperkalemia than dogs so all diets promote potassium supplementation.  What is interesting to note is that all five diets have potassium level that are either very similar to what is found in the natural prey diet, or are actually below.  Some Internists argue it is not a bad idea to keep diets slightly hypokalemic because there has been a few case reports of animals going hyperkalemic from eating a high potassium diet, so if the diet is kept slightly deficient, it allows us veterinarians to modify the diet better.

Comparison of the (abbreviated) typical analyses of the different feline canned diets

Table 5.2: Comparison of the (abbreviated) typical analyses of the different feline canned diets

Nutrient (g/1000 kcal)	Natural Prey Diet	Eukanuba: Multi-Stage	Hills: k/d	Purina: NF	Medi-cal: Reduced Protein	Royal Canin: Renal LP
Crude Protein	151.00	66.12	64.80	67.02	53.70	56.00
Crude Fiber	4.50	5.07	6.73	8.67	3.10	5.80
Phosphorus	5.00	1.58	0.85	1.22	0.90	0.80
Potassium	2.00	1.90	2.65	3.16	1.90	2.30
Sodium	1.00	1.16	0.67	0.49	0.50	0.70
Chloride		1.58		1.38
Omega 3 FA			1.61	2.19
Omega 6 FA		9.22		6.89
Omega 6 : 3	3 : 1	5 : 1		3 : 1

Once again, while all their packages say they have added omega 3 and 6 to their diets, Purina is the only one that tells us exactly how much was added and unlike their dry kibble, the ratio is the ideal 3:1.  Eukanuba has also listed their omega 6:3 ratio but they do not have enough omega 3’s in their diet for the amount of omega 6 present.

The caloric distribution of the canned feeds is very similar to the dry kibble.  Like to their dry kibble, all diets are protein restricted with an average of 61.53g/1000 kcal.  Once again, Purina has the highest crude protein level but Eukanuba is the one with the nitrogen fibre trap system.  Similarly, the crude fibre content is quite comparable between diets.  What is different is that the canned feeds are higher in fat than the dry kibble but even then, the different is not very large so its significance can be arguable. 

Once ag ain the nutrient breakdown of the canned feeds is very similar to that of the dry kibble diets.  Similarly, calcium is still lower than what is found in the natural prey diet (but the same arguments can apply here as it did with the dry kibble diets) as is phosphorus and sodium (with the exception of Eukanuba’s  sodium levels).  Once again, even though all companies say they supplement potassium, some diets (Eukanuba and Medi-cal) are still below that of the natural prey diet; although, in general, the canned diets have a higher potassium content than the dry kibble equivalent.

Comparison of the primary ingredients used in the different feline dry kibbles

Table 6.1:  List of the primary ingredients used in the different feline dry kibbles

Eukanuba: Multi‑Stage	Hills: k/d	Purina: NF	Medi-Cal: Reduced Protein	Royal Canin: LP
Corn grits	Brewer’s rice	Brewer’s rice	Rice flour	Pork meal
Chicken	Corn gluten meal	Whole grain corn	Corn	Corn
Corn gluten meal	Pork fat	Corn gluten meal	Chicken fat	Chicken fat
Chicken fat	Chicken by-product meal	Soybean meal	Chicken meal	Rice
Soy protein isolate	Dried egg product	Animal fat	Corn gluten meal	Wheat
Dried beet pulp (sugar removed)	Dried chicken	Animal digest	Fish meal	Corn gluten meal
Gum arabic	Powdered cellulose	Fish meal	Dried egg powder	Powdered cellulose
Fish oil	Fish meal	Calcium carbonate	Potato protein	Natural flavour
Natural chicken flavour	Chicken liver flavour	Potassium citrate	Dried beet pulp	Wheat gluten
Fructo-oligosaccharides	Calcium carbonate	Phosphoric acid (palatability)	Natural flavour	Chicory pulp
Calcium carbonate	Dried beet pulp	Potassium chloride	Fish oil	Fish oil

Table 6.2:  Comparison of the primary ingredients used in the different feline dry kibbles

	Eukanuba	Hills	Purina	Medi-Cal	Royal Canin
Carbohydrate	Corn grits, corn gluten meal	Brewer’s rice, corn gluten meal	Brewer’s rice, whole grain corn, corn gluten meal	Rice flour, corn, corn gluten meal	Corn, rice, wheat, corn gluten meal, wheat gluten
Protein	Chicken, soy protein	Chicken by-product meal, dried egg product, dried chicken, fish meal	Soybean meal, animal digest, fish meal	Chicken meal, fish meal, dried egg product, potato protein	Pork meal
Soluble Fibre	Dried beet pulp, gum arabic, fructo-oligosaccarides	Dried beet pulp		Dried beet pulp	Chicory pulp
Fat	Chicken fat, fish oil	Pork fat	Animal fat	Chicken fat	Chicken fat
Omega 3 & 6 Source	Fish oil	Fish meal	Fish Meal	Fish meal, fish oil	Fish oil
Buffers	Calcium carbonate	Calcium carbonate	Calcium carbonate, potassium citrate

What is interesting to note is the similarities between the different diets.  In regards to the carbohydrates source, all diets use corn or rice primarily.  Corn has its benefits for renal diets because it has an average level of proteins (as opposed to elevated like with barley or rice bran) and is a good source of linoleic acid.  Rice and brewers rice is also a good choice because it is low in phosphorus (as opposed to barley or rice bran again).  Royal Canin is the only one who has some wheat gluten but because wheat is higher in protein than the corn or rice, Royal Canin can use less of its other protein sources.  Use of vegetable proteins over meat proteins may have its benefits too because they are more digestible and in humans, has some evidence of halting disease progression without compromising nutrition. 

Their choice of primary protein sources are quite similar too: chicken (fresh, dried, meal or by-product), soy (protein or meal), dried egg product, or fish meal.  Once again, Royal Canin is unique in that it uses pork meal instead.  Even though Eukanuba and Medi-cal are the only ones who promote their fibre content, all but Purina has a soluble fibre source as one of their primary ingredients.  Another similarity between the companies is the use to fish meal or fish oil to add omega 3 and 6 to their diets.  Even though all companies have some form of buffer in their diet, Eukanuba, Hills and Purina are the only ones who have it in their primary ingredients lists.

Comparison of the primary ingredients used in the different feline dry kibbles

Table 6.3:  List of the primary ingredients used in the different feline canned feeds (minus water are the first ingredients)

Eukanuba: Multi‑Stage	Hills: k/d	Purina: NF	Medi-Cal: Reduced Protein	Royal Canin: LP
Beef liver	Pork liver	Poultry by-product	Pork by-product	Pork by-product
Chicken	Chicken	Beef	Chicken	Chicken liver
Beef by-product	Pork by-products	Rice	Chicken liver	Chicken by-products
Corn meal	Brewer’s rice	Meat by-product	Chicken fat	Corn flour
Chicken Fat	Oat fibre	Chicken	Pork	Chicken
Corn Starch	Corn starch	Oat fibre	Fish oil	Fish oil
Dried egg product	Glucose	Calcium gluconate	Brewer’s rice	Vegetable oil
Dried beet pulp	Chicken fat	Fish oil	Rice flour	Starch
Gum arabic	Potassium citrate	Guar gum	Mackerel	Dried egg white
Fish oil	Psyllium seed husk	Potassium citrate	Calcium carbonate	Powdered cellulose
Fructooligosaccharides	Guar Gum	Potassium chloride	Potassium citrate	Potassium citrate

Table 6.4:  Comparison of the primary ingredients used in the different feline canned feeds (minus water are the first ingredients)

	Eukanuba	Hills	Purina	Medi-Cal	Royal Canin
Carbohydrate	Corn meal, corn starch	Brewer’s rice, oat fibre, corn starch	Rice, oat fibre	Brewer’s rice, rice flour	Corn flour, starch
Protein	Beef liver, chicken, beef byproduct, dried egg product	Pork liver, chicken, pork byproduct	Chicken byproduct, beef, meat byproduct, chicken	Pork byproduct, chicken, chicken liver, pork	Pork by-product, chicken liver, chicken byproduct, chicken, dried egg white
Soluble Fibre	Dried beet pulp, gum arabic, fructooligosaccaride
Fat	Chicken fat, fish oil	Chicken fat	Fish oil	chicken fat, fish oil	Fish oil, vegetable oil
Omega 3 & 6 Source	Fish oil		Fish oil	Fish oil, mackerel	Fish oil
Buffers		Potassium citrate	Calcium gluconate, potassium citrate	Calcium gluconate, potassium citrate	Potassium citrate

The primary ingredients list for the canned diets is very similar to the dry kibble.  Once again, corn and rice are the common grains used for carbohydrate sources and most diets have fish oil or fish contributing  to the omega 3 and 6 fatty acids.  Addition of a buffer is seen in all but Eukanuba.  What is different is the choice of protein.  Fresh and by-product is more common in the canned feeds than dry kibbles but is likely related to the fact that meals are dry and may be difficult to put into canned feed.  Liver (beef, pork or chicken) is a common protein source in canned feeds that is not seen in the dry kibble – this is good because it provides a balanced source of amino acids.  Unfortunately, because of the high water content of canned diets, most are are lacking a soluble fibre source in their primary ingredients list – Eukanuba is the only one with soluble fibre and they have all three ingredients that make up their nitrogen trap system. 

Best diet

Due to the similarities between all five diets, it is very difficult to decide on a single diet that is “best”.  Like the dog, palpatibility is likely the most important aspect because a prescription diet is only good if the cat will eat it.  When deciding which diet to start with, it may be good to consider that:

·        Medi-cal is the least phosphorus restricted but with that said, it is only barely elevated and such may not be significantly higher

·        All diets may supplement potassium but Eukanuba and Hills are still lower than what is seen in the natural prey diet

·        Eukanuba does not restrict sodium so that may be an issue if you believe sodium has an important role in initiating system hypertension

·        While Royal Canin and Medi-cal both have buffers in their diet, they are the only ones that do not have it in their primary ingredients list

·        Purina lacks soluble fibre in its dry kibble and canned feed

Unfortuantely without further studies into what a cat’s nutritional requirements are and into what an ideal renal diet should be, we have to conclude that all five diets are equivalent.

Table 7:  Cost comparison for a 3-kg cat based on daily energy requirement and prices at the Western College of Veterinary Medicine: Veterinary Teaching Hospital 

	Eukanuba: Multi-Stage	Hills: k/d	Purina: NF	Medi-Cal: Reduced Protein	Royal Canin: Renal LP
Dry Kibble	$0.51	$0.71	$0.48	$0.49	$0.56
Canned Feed	$1.68	$2.24	$1.88	$1.72	Unavailable

A cost comparison of the diets were performed for a 3kg cat and it found that Hills is the most expensive diet but the others are quite similar in cost (both dry kibble and canned feed).

Can non-renal diets be used

For whatever reason, not all clients wish to purchase prescription diets.  Many ask to use an over the counter diet instead.  To this effect, we compared the average of the renal diets with three non-renal diet to see if the same goals can be achieve.  The three diets we chose are Science Diet: Light Adult, Science Diet: Mature Active Longevity Savoury Chicken and Medi-cal: Weight Loss.  The reason for the weight loss diets is because they are supposed to be protein and fat restricted already and high in fibre.  Even though Medi-cal: Weight Loss is not an over the counter diet, we examined it because that is the diet recommended for cats in renal insufficency without significant proteinuria.

Table 8:  Comparison of renal and non-renal feline diets; dry kibble

	Natural Prey Diet	Hills: k/d	Science Diet: Light Adult	Science Diet: Mature Active Longevity	Medi-cal: Weight loss
Crude Protein	151.00	67.68	99.63	80.96	89.50
Crude Fiber	4.50	4.23	19.59	5.28	9.22
Phosphorus	5.00	1.08	2.07	1.66	2.44
Potassium	2.00	1.76	1.90	2.11	2.25
Sodium	1.00	0.56	1.14	0.77	1.27
Chloride	0.00
Omega 3 FA		0.33
Omega 6 FA
Omega 6 : 3	< 3 : 1

As can be seen from Figure 7.1, the renal diets are more protein restricted than the non-renal diets but they are all restricted compared to the natural prey diet; Science Diet: Mature is the most protein restricted of the non-renal diets.  What is interesting to note with regards to the crude fat is that low protein is compensated with higher fat levels; regardless all diets are lower than the natural prey diet.  Both weight loss diets have a higher fibre content than the others. 

When the nutrient breakdown is examined more closely, it can be concluded that the three non-renal diets are quite similar to the renal diets but they are not as phopshorus or sodium restricted.  The potassium levels are about equivalent between all diets. 

These trends are all similar to what can be seen with the canned diets.

Table 9:  Comparison of renal and non-renal feline diets; canned feed

	Natural Prey Diet	Hills: k/d	Science Diet: Light Adult	Science Diet: Mature	Medi-cal: Weight loss
Crude Protein	151.00	64.80	99.40	89.26	99.18
Crude Fiber	4.50	6.73	28.20	8.42	10.50
Phosphorus	5.00	0.85	1.93	1.57	2.33
Potassium	2.00	2.65	2.15	1.87	2.22
Sodium	1.00	0.67	0.89	1.12	1.75
Chloride	0.00
Omega 3 FA		1.61
Omega 6 FA
Omega 6 : 3	< 3 : 1

Given the similarities between the feline renal and these select non-renal diets, cats in chronic renal failure may potentially be maintained on a non-renal diet.  The weight loss and senior forumlations examined in this project are already lower in protein and phosphorus than the natural prey diet and have similar potassium and sodium levels than the renal diets.  Of the three non-renal diets examined, Science Diet: Mature Adult Longevity is probably the best choice because it has the lowest protein levels, the most phosphorus restriction.  With that said, the three are so similar the differences may not stastically different.

Homemade renal diets for dogs:

Makes one serving

·        100g                     Broiled lean ground beef (70% fat)

·        ¼ cup                   Kellogg’s All Bran (with extra fibre), as is

·        3 cups                  Cooked white rice, medium grain

·        0.5 tablets           Centrum Multivitamins

·        500 mg                Tums

·        A pinch                              Salt substitute (potassium chloride; eg. AlsoSalt)

Figure 9.1: Comparison of caloric distribution between the homemade diet and the Hills: k/d (kibble)

Figure 9.2: Comparison of nutrient breakdown between the homemade diet and the Hills: k/d (kibble)

Homemade renal diet for cats:

Makes one serving

·        1/8 of a fillet       Cooked salmon

·        1 patty                 Cooked (frozen) beef patty

·        ¼ tbsp                  Table salt

·        1 tablet                Centrum Multivitamins

·        1000 mg              Tums

·        ¼ capsule           Taurine capsule (for body builders)

Figure 10.1: Comparison of caloric distribution between the homemade diet and the Hills: k/d (kibble)

Figure 10.2: Comparison of nutrient breakdown between the homemade diet and the Hills: k/d (kibble)

References – Books and Journal Articles

1.      Alphonse, M Hadj-Abdelkader and C Remesy.  Fermentable carbohydrate and    digestive nitrogen excretion. 2001. J Renal Nutr. 11(3): 139-148.

2.      Bernstein AM, L Treyzon, and Z Li. Are high-protein, vegetable-based diets safe for kidney function? A review of the literature. 2007. J Am Diet Assoc.  Apr;107(4):644-50.

3.      Brown SA, Brown CA, Crowell WA, Barsanti JA, Kang CW, Allen T, Cowell C, and Finco DR. Effects of polyunsaturated fatty acid supplementation in early renal insufficiency in dogs. 1996. J Lab Clin Med. 135: 275-286.

4.      Buranakarl, C, Mathur S, and Brown SA. Effects of dietary NaCl intake on renal function and BP in cats with normal and reduced renal function. 2004. AJVR. May;65(5): 620-627.

5.      Burkholder, W. Dietary considerations for dogs and cats with renal disease. 2000. JAVMA. June; 216: 1730-1734.

6.      Daristotle L, MA Tetrick, DP Carey, DM Waltz, and PL Stockton.  Iams: Current concepts in clinical nutrition for dogs and cats. 2002. Harcourt Health Communications.

7.      Elliott, J, Rawlings JM, Markwell PJ, and Barber PJ. Survival of cats with naturally occurring CRF: effect of dietary management. 2000. Journal of Small Animal Practice. 41: 235-242.

8.      Hand and Novotny.  Pocket companion to small animal clinical nutrition. 4th edition. 2002. Mark Morris Institute.

9.      Laflamme, D. Pet Food Safety: Dietary Protein. 2008. Topics in Companion Animal Medicine. 23(3): 154-157.

10.   Jacob F, Polzin DJ, Osborne CA, Allen TA, Kirk CA, Neaton, JD, Lekcharoensuk C, and Swanson LL. Clinical evaluation of dietary modification for treatment of spontaneous chronic renal failure in dogs. 2002. JAVMA. 228(8): 1163-1170

11.   Pibot, P., Biorge, V., and Elliot, D. Encyclopedia of Canine Clinical Nutrition. 2006. Aniwa SAS (on behalf of Royal Canin).

12.   Polzin DJ and CA Osborne. The importance of egg protein in reduced protein diets designed for dogs with renal failure. 1988. J Vet Intern Med. Jan-Mar;2(1):15-21.

13.   Polzin DJ, Osborne CA, Ross S, and Jacob F. Dietary management of feline CRF: where are we now? In what direction are we headed? 2000. Journal of Feline Medicine and Surgery. 2: 75-82.

14.   Nelson, RW and CG Couto.  2003.  Small animal internal medicine.  3rd edition.  Mosby, Inc.

15.   Ross SJ, Osborne CA, Kirk CA, Lowry SR, Koehler LA, and Polzin DJ. Clinical evaluation of dietary modification for treatment of spontaneous chronic kidney disease in cats. 2006. JAVMA. 229 (6): 949-954.

16.   Younes H, K Garleb, S Behr, C Remesy and C Demigne.  Fermentable fibers or oligosaccharides reduce urinary nitrogen excretion by increasing urea disposal in the rat cecum. 1995. J Nutr. 125:1010-1016.

References from pet food company websites

Hill’s

17.   Allen TA, Yu S. Antioxidants and Renal Function. Hill’s Veterinary Conference Proceedings.

18.    Cowgill LD, Francey T. New Directions for the Medical Management of Renal Disease. Hill’s Veterinary Conference Proceedings.

19.   Polzin, JP. Salt, Water, and Blood Pressure – Are they Related? Hills Veterinary Conference Proceedings.

20.   Polzin DP, Osborne CA, Jacob F, Ross S, Swanson, L. The Role of Nutritional Management in Dogs with Chronic Kidney Disease. Hill’s Veterinary Conference Proceedings.

21.   Ross S, Osborne CA, Polzin DP et. al. 2005. A Condensed Study Review – Clinical Evaluation and Effects of Dietary Modification in Cats with Kidney Disease. Hill’s Nutritional Research Review.

Purina

22.   Nestle-Purina Research Report for the Veterinarian. 2006. 10(2).

23.   Nestle-Purina Research Report for the Veterinarian. 2006. 10(3)

24.   Nestle-Purina Research Report for the Veterinarian. 1998.

Medi-Cal/Royal-Canin

25.   Houston DM, Armstrong, J. Feeding the Patient with Renal Disease. Technical Report 016-17.

Iams/Eukanuba

26.   Food for Thought Veterinary Technical Bulletins – various