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Written by leading veterinarians to provide you with the information you need to care for your pets.

The Daily Vet by petMD

The Daily Vet is a blog featuring veterinarians from all walks of life. Every week they will tackle entertaining, interesting, and sometimes difficult topics in the world of animal medicine – all in the hopes that their unique insights and personal experiences will help you to understand your pets.

Following last week’s post, this is the next installment of interesting nutritional information that was presented at the Annual Clinical Nutrition and Research Symposium. The symposium is organized by the American Academy of Veterinary Nutrition and is held in conjunction the annual American College of Veterinary Internal Medicine scientific conference. It features oral and poster presentations of abstracts of recent or soon to be published scientific studies. This year’s venue was held at the Washington State Convention Center in Seattle.

Dietary Protein and Kidney Disease

For years, dietary protein restriction has been the hallmark management tool for veterinarians treating chronic kidney disease in dogs and cats. This is a result of an old study that determined that the survival time was three times longer for dogs fed a low protein diet compared to dogs fed a regular protein diet.

The study had several flaws but without sound research to the contrary, it has remained the “gold standard” of kidney disease management. Many veterinarians, myself included, have questioned the wisdom of this approach but substantiating research has been lacking. A new study questions this age old practice.

The double-blind, randomized study compared actual kidney function, creatinine (a blood marker for kidney function), body condition and survival time of dogs fed a low protein diet (16%) and those fed a normal diet (22.5% protein). Both diets had the same restricted phosphorus content. What they found was no significant difference in kidney function, blood creatinine levels or survival time between the two groups. As expected the body condition scores were greater for the normal protein group as they maintained more muscle mass. The main determinant of survival time was the level of kidney dysfunction at the time of diagnosis, not the diet.

What is interesting is that the low protein diet in this study was 2-3 percent greater than most of the veterinary diets formulated for kidney disease. That means that muscle loss would be expected to be even greater for pets being fed veterinary kidney diets. The maintenance of muscle mass has implications for maintaining an active lifestyle. Since quantity of life is no different it would make sense to feed kidney patients a normal protein diet to maintain their quality of life. This study also suggests that phosphorus control is more important than dietary protein in kidney patients.

The Protein Needs of Cats

A poster presentation featured a study to determine the necessary protein requirement for aging cats to maintain lean body mass. Researchers matched four groups of ten cats and fed them diets of varying protein content. The cats were fed adequate calories to maintain their weight for the six month study.

Each cat’s lean body mass was determined by a special technique called DEXA (dual-energy X-ray absorptiometry) at the beginning of the study, at three months and at six months. They found that cats needed at least 2.5 grams (.09 oz.) of protein per pound of body weight daily to maintain ideal lean body mass. Cats fed less protein than this necessarily replaced muscle with fat in order to maintain the same body weight. These finding are greater than the present protein recommendations of both the National Research Council (NRC) and Association of American Feed Control Officials (AAFCO) guidelines.

This suggests that many cat foods are not meeting the protein requirements necessary to promote optimum lean body mass for older cats. Pet food labels are not required to give detailed information about protein, fat and carbohydrate content. Finding how many grams of protein your cat is getting from its diet will require researching the company’s website or talking to a company nutritionist. Even after that, the exact amount of protein may require further mathematical calculations. We really need pet food labels like those on our food!

Dr. Ken Tudor

Image: Thinkstock

Comments  4

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  • Thank You!
    06/27/2013 06:11pm

    Thank you for the information on protein content for kitties. This makes me feel a whole lot better about feeding several of my CRF kitties their regular diet simply because they refused to eat prescription food. It sounds as if we need to maybe increase the protein content accordingly as our healthy kitties age. It may not have been enough protein, but it was better than if I had fed them a protein-restricted diet.

    As an aside, my rule of thumb has always been, "I'd rather have them eat the wrong thing than *no* thing."

  • TheOldBroad
    06/27/2013 09:44pm

    Couldn't agree with you more unless there is compelling evidence to the contrary. I think we vets sometimes forget to look at cases holistically and advise our clients on quality of life vs. quantity of life. We are so preoccupied with our role as "healers" we forget that "nature heals, we collect." Thanks for your continued readership and comments.

  • Low Phos v Low Protein
    03/20/2014 05:26pm

    So interesting Dr. Tudor. I've been consulting and exchanging information with our veterinarian concerning our 15+ year-old dog determined to be in kidney failure last year. Phos is normal, but our previous vet prescribed phosphate binder - this was called to our attention by the mobile vet we moved to who reviewed September and October lab results from other vet and said phos was normal then and now, so we don't know why he wanted us to give phosphate binder. That said, I've read quite a bit online about the topic of restricting protein and really appreciated this post because I'd called our current DVM's attention to the 'controversy' and she said there is consensus among the overwhelming majority of veterinary kidney specialists that a diet formulated for kidney disease (moderately lower in protein, lower in phosphorus and sodium, higher in potassium, higher in fatty acids) is very beneficial. She also said you can't lower phosphorous in the diet without also lowering protein, which seems to be contradicted by your post here. Can you comment. Thank you so much!


  • 03/20/2014 06:11pm

    I would love to give you a link to share for the study I talked about but it is still not in print.
    I think the confusion with your vet is about the content level of phosphorus in meat protein. Yes indeed meat is high in phosphorus and lowering the protein content of food will lower the phosphorus. However she is assuming that the phosphorus contained in an adequate amount of protein meets the phosphorus needs of dogs. After formulating homemade diets for years, I can tell you that meeting an individual dogs needs for protein still leaves them deficient in phosphorus. Added that dogs can only absorb about 30% of the phosphorus in vegetable and grain sources means that homemade and commercial dog foods must add a source of phosphorus to be nutritionally complete. What this means for kidney patients is that they can have a normal amount of protein yet a low phosphorus diet simply by the choice of carbohydrates in the diet and restricting the phosphorus supplementation.
    I hope this clarifies the issue for you. Thanks for the question.

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