Should protein always be limited for dogs and cats with chronic kidney disease (CKD)?

Scientific knowledge is durable, but it does not represent absolute truth. Science continues to evolve by questioning new evidence and reexamining previous conclusions.

Protein restriction for the management of kidney disease in dogs and cats has been a mainstay of therapy for many years. Nevertheless, protein restriction as a nutritional strategy in nephropathic patients has become a controversial topic. Indeed, studies showing increased longevity in dogs and cats fed a therapeutic kidney diet rather than a maintenance diet are unable to distinguish the beneficial effects of protein restriction from the advantages of phosphorus reduction and other features of therapeutic kidney diets.

Dogs and cats with chronic kidney disease (CKD) often develop cachexia or loss of lean body mass (LBM) and body weight. A recent study found that underweight dogs, i.e., with a body condition score (BCS) of 1 to 3 out of 9, have lower survival than dogs with a BCS of 4 or higher (Parker at al., 2011). This is the main reason why some authors consider it unreasonable and disadvantageous to administer a low-protein diet to dogs and cats with CKD. Dogs and cats with early stages of CKD (IRIS stages 1 and 2) will likely tolerate higher concentrations of protein as compared to those with severe azotemia.

In addition to the amount of protein in the diet, it is necessary to consider the quality of protein. Protein quality depends on the amino acid composition of a particular protein source and is measured by the bioavailability of the amino acids it contains (AA), i.e., the efficiency with which the amino acids are converted to tissues. A high quality protein contains all the essential amino acids for the species.

The amino acid profile may vary from diet to diet even if the crude protein content is similar. Diets high in protein but low in AA may not be able to maintain optimal LBM.

Because in the veterinary literature, no definitive conclusion has been reached regarding which diet is more beneficial for dogs and cats with CKD -whether an unrestricted protein diet with the other features of therapeutic renal diets or a therapeutic protein-restricted renal diet- it would be advisable to consider each patient as a unique individual and to vary nutritional management according to the different forms of CKD, that is, the IRIS stage and sub-stages of the disease.

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References

Parker VJ. Nutritional Management for Dogs and Cats with Chronic Kidney Disease. Vet Clin North Am Small Anim Pract. 2021 May;51(3):685-710. doi: 10.1016/j.cvsm.2021.01.007. Erratum in: Vet Clin North Am Small Anim Pract. 2021 Sep;51(5):ix. PMID: 33773648.

Sanderson SL, Tetrick M, Brown SA, et al. Effect of dietary approach on clinical outcome measures in dogs with naturally occurring chronic kidney disease (abstract). J Anim Physiol Anim Nutr 2013;97:1198–9.

Parker VJ, Freeman LM. Association between body condition and survival in dogs with acquired chronic kidney disease. J Vet Intern Med 2011; 25(6):1306-1311.

Bovee, Kenneth C.. “Mythology of Protein Restriction for Dogs with Reduced Renal Function.” (1999).