Per @Glennlivet: link
http://www.greyhoundgang.org/medical-kidney.phpAn article from 1998 Purina Nutrition forum specically on this issue is available online. It's: "Mythology of Protein Restriction for Dogs with Reduced Renal Function" by Kenneth C. Bovee DVM, MMedSc.
http://www.vetshow.com/download/purina/finco.pdfHere's some excerpts from Dr. Bovee's article:
"there is evidence that high protein diets enhance renal function in normal dogs. This has led to confusion among veterinarians who have been told for decades that low protein diets may be beneficial for kidney function and therefore high protein diets may be deleterious to normal dogs."
"Because of the confusion in the veterinary literature and the lack of evidence to support the use of reduced protein diets, a number of experimental studies have been performed in recent years. These studies have utilized the standard experimental model of reduced renal function and have addressed many questions when dogs received varied forms and
quantities of protein at different levels of renal function. [...] Results of the 10 experimental studies on dogs have failed to provide evidence of the benefit of reduced dietary protein to influence the course of renal failure."
"Based on the previous data, the only advantages [of dietary protein restriction in dogs] appear to be a lowering of BUN and the possibility of reduced nausea. Quantifying the value of these effects has not been reported in dogs. On the contrary, there appear to be disadvantages to reduced protein intake. These include reduced kidney function as
measured by GFR [glomuleral filtration rate] and renal plasma flow, possibility of a negative nitrogen balance, and the promotion of a catabolic state in the presence of proteinuria."
If you'd like to read a review of the current studies on this, there's a good summary in the article: "Effects of Dietary Protein Intake on Renal Functions" by Delmar R. Finco in Purina Nutrition Forum 1998. This is available online at:
http://www.vetshow.com/download/purina/finco.pdf In part, Dr. Finco states:
"When attention is focused on those experiments in which protein has been isolated as the only variable, the data are overwhelmingly indicative of a failure to demonstrate a protein effect on the functional or morphological deterioration of kidneys of "remnant kidney" dogs."
He has a table summarizing the various studies. In some of the studies, the diets varied in other components as well as varying in protein. But of the studies that varied ONLY the protein, there were no differences noted in kidney function in the different study groups.
One study had dogs with 15/16ths of their kidneys removed on diets of either 16% or 31% protein for 24 months and the result was: "No differences in deterioration of renal function or in severity of renal lesions." (Finco, DR, Brown, SA, Crowell WA, et al: Effects of dietary
phosphorus and protein in dogs with chronic renal failure. Am. J. Vet. Res. 53:2264-2271, 1992.) Another study had diets of 14% or 40% protein fed to dogs who had 11/12ths of their kidneys removed. They were fed these protein levels for 100 weeks. The result: "No functional deterioration with time with either diet; no difference in severity of
renal lesions between diets." (Polzin DJ, Osborne CA, O'Brien TD, et al: Effects of protein intake on progression of canine chronic renal failure (CRF). Proceedings of the 11th Annual Veterinary Medical Forum, 938, 1993.)
So what should people feed their dogs with renal failure? Restricted phosphorus diets, for one thing. Restricting phosphorus is one dietary change that has been shown to prolong the lives of dogs in renal failure. Aside from restricting phosphorus intake, phosphorus binders can be used to prevent absorption.
Most commercial 'kidney diets' such as k/d were low-protein because that was the old theory. Now that low protein is counter-indicated in early stage renal disease, what DO you feed? Well, the problem is that most higher protein foods are also higher in phosphorus. Dairy and eggs are relatively low phosphorus considering their protein content and can be added to senior or 'kidney' diets to help boost protein levels.
A Fall 1999 article on Nutritional Management of Dogs and Cats with Chronic Renal Failure by Dr. Tina Kalkstein, a board certified veterinary internist. (Her portrait on this site shows her on the beach with a brindle, a fawn, and a black greyhound, btw.):
http://www.southpaws.com/news/99-2-nutrition-CF.htm"CRF patients should be fed the maximal amount of protein they can tolerate until clinical signs of uremia develop. Once this occurs, the protein intake should be tailored to meet the needs of the patient. If the dog or cat loses weight, coat condition, or serum proteins on a low protein diet, but feels otherwise good, consider adding additional protein to their daily meals (egg, cottage cheese, tofu, etc.) or choosing a different diet that is less protein restricted until finding the individual's tolerable threshold of protein intake. Acid-base status should also be monitored and corrected as needed (adding bicarbonate to the drinking water is a simple way to manage mild to moderate acidosis).
Phosphorus levels are important to monitor and manage as well."
Excerpt from Iams Nutrition Symposium (May 1998):
http://www.eukanubacatfood.com/vet/symposium/building/building.html"For decades, without scientific validation, veterinarians have attempted to decrease nitrogenous waste products by simply limiting the protein substrate; low-protein diets have been a staple in the nutritional management of chronic renal failure patients. However, recent studies by Dr. Gregory A. Reinhart and fellow Iams nutritionists show that restricting protein may do more harm than good. "Excessive restriction of protein," he said, "puts many companion animals at risk of protein malnutrition." Also, carnivores find low-protein diets less than palatable, especially animals already nauseous and anorexic from renal failure. Iams' research shows not only that optimal protein levels do not harm the kidneys, but that they benefit the patient by maintaining muscle mass and increasing energy."
"Defining "optimal" is the challenge. Dr. Reinhart said veterinarians need to "match the level of protein restriction with the stage of disease progression" in what he termed a "nutritional balancing act." Clinical trials by Dr. Mark A. Tetrick, Iams Veterinary Nutritionist, have indicated that dogs in early chronic renal failure may be successfully fed approximately 50 percent more protein than is found in conventional renal diets. Dogs with advanced renal failure can safely be fed approximately 25 percent more protein. The dogs fed the higher protein diets looked better, based on coat condition, and had no adverse serologic effects. Their blood urea nitrogen (BUN) levels remained the same or went down, and their triglyceride levels actually fell. Dr. Tetrick also found that blood phosphorus levels went down as a result of the extremely low phosphorus content of these diets. Phosphorus restriction has been shown to slow the progression of renal disease."
Here's some of the current recommendations from Ohio State's vet school
http://nss.vet.ohio-state.edu/Vm%20720/Nutrition%20and%20Chronic%20Renal%20Failure.html"Results of recent research are changing our recommendations for nutrient modification in dogs with early signs of CRF. Restricting phosphorus intake to about 30 mg/pound/day as soon as polyuria is recognized, and supplementing potassium intake (with alkalinizing salts if acidosis is a concern) to maintain serum potassium within the normal range may be all that is necessary until patients develop severe disease. Diet change or phosphorus binders, such as aluminum hydroxide, calcium carbonate, or calcium acetate may be used to restrict phosphorus absorption. Phosphate binders and potassium supplements can be added to the diet in small amounts initially, and increased as the patient's tolerance and condition permits."
Sodium restriction may be beneficial to animals suffering systemic hypertension, but should be introduced gradually. Animals with CRF have lost most of their renal reserve capacity, and cannot quickly adapt to large abrupt changes in nutrient intake. Modification of the fatty acid composition of diets to reduce the n-6 to n-3 fatty acid ratio also may be beneficial, and studies to address this point currently are in progress.
Hope this helps. I lost a dog to renal failure and I know how heartbreaking it can be. There's not much you can do in the way of treatment outside of dietary management, so it's very frustrating to realize (as I did) that the perfectly nice vet you're using had probably not read a vet journal article on renal failure and diet in the last 10 years, so he was recommending that we do something less than useless.
If I had a dog with renal failure today, I'd probably buy the highest protein of the current renal diets - I know that Iams touts theirs as being higher than most. I'd add protein from relatively low-phosphorus but high quality sources like cottage cheese if the dog seemed hungry all the time or did not find the food to be palatable on its own.
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