C. Villaverde Haro
Chronic kidney disease (CKD) is a common disease in both dogs and cats, especially those of advanced age. Clinical trials support the use of specific diets that improve both survival and quality of life.1,2 Dietary management is the main treatment of this disease in both species.3 Nutritional modifications include phosphorus restriction, protein and sodium moderation, B-vitamin supplementation and alkalinization. Potassium content is variable but tends to be higher in feline CKD diets vs maintenance. Some CKD diets also include long-chain omega-3 fatty acids EPA and DHA.
A complete nutritional evaluation (https://wsava.org/global-guidelines/global-nutrition-guidelines/) should be carried out before making recommendations. The evaluation includes diet and medical history and a complete physical exam, including body condition score (BCS) and muscle condition score (MCS).
When to Start Feeding a CKD Diet
Clinical studies have seen benefits of CKD diets in stages II to IV; it is unknown if using such a diet would be beneficial in stage I (unless there is proteinuria). That said, the better the patient feels, the easier to switch diets. Several manufacturers have early-stage CKD diets, with the same modifications but in a less aggressive manner.
Diets for CKD have the following modifications: Phosphorus restriction addresses renal secondary hyperparathyroidism. The IRIS society (http://www.iris-kidney.com/) recommends the use of low phosphorus diets early in the disease. In later stages, phosphate binders will be required where dietary restriction is not enough.
We do not know the effect of dietary sodium on renal or systemic hypertension, so CKD diets are not really restricted but provide moderate sodium, below typical maintenance diets. A very low sodium diet is not desirable, since it stimulates the renin-angiotensin-aldosterone axis and results in hypertension.4 Potassium varies amongst renal diets. Some patients (especially canine) can show hyperkalemia, associated for example to treatment with ACE inhibitors, and they respond well to dietary moderation of potassium.5 Protein is never restricted in CKD patients, because it is required for body functions. However, the goal is to avoid excess, to minimize nitrogen waste products. For this reason, CKD diets should provide moderate protein amounts of a high biological value and digestibility, to avoid creating essential amino acid deficiencies. Protein moderation seems to help more with quality of life than survival3, with the possible exception of proteinuria, where it helps reduce protein losses. The NRC6 minimum protein requirement for dogs is 8% protein calories and for cats 16% protein calories, while AAFCO recommendations for adults are, respectively, 16 and 22%. All CKD diets exceed NRC requirements in dogs, and in cats they all exceed AAFCO protein requirements for healthy pets. However, protein deficiency can occur in patients with poor appetite that do not eat enough. An inadequate energy intake will result in muscle mobilization.
Diets for CKD should have high B-vitamin concentrations to compensate for increased losses due to polyuria.
Diets for CKD promote alkalinization to help manage the acidosis that is caused by the disease.
EPA and DHA have shown positive effects on experimental canine CKD7, and one retrospective study in cats suggested that diets rich in these fatty acids could result in longer survival8, but we need more prospective research in both species with spontaneous disease.
Per the above, it is indicated to choose a commercial CKD diet of a reputable brand. Diets differ in the degree of nutritional modifications but also on energy density, palatability, texture, etc. Choice will be affected by price, availability, palatability, and how well the nutrient characteristics of the diet match the nutritional evaluation of the patient. Treats can be given, as long as they provide less than 10% of the total daily calories and follow the same strategies as the main diet.
If a homecooked diet is desired, consult a specialist (https://acvn.org/, https://www.esvcn.eu/) to get a customized recipe.
Amount to Feed
The amount of food should be enough to maintain a stable body weight and ideal BCS. Label instructions are a good start (or formulas, such as https://wsava.org/wp-content/uploads/2020/01/Calorie-Needs-for-Healthy-Adult-Cats.pdf), but they will need twice-a-month adjustments, since formula error is common. Patients with low BCS should be fed 20% more than label instructions/formulas. Weight loss can be attempted in overweight patients if it negatively affects quality of life. In that case, we aim for a weight loss rate of <0.5% body weight per week.
Thin animals with picky appetite will benefit from either ad libitum feeding or multiple meals per day. Normal weight patients can be fed ad libitum as well, unless they are obese prone. If they are obese prone or already overweight, portion control is indicated.
In addition to standard CKD monitoring (via physical exam, bloodwork, urinalysis, medical history), regular nutritional evaluations (including weight, BCS, muscle mass, food intake, etc.) are important to adjust the plan.
What to Do If They Do Not Eat the Diet
Hypo- and anorexia should always be worked up. There might be issues that can be managed, such as dehydration, anemia or nausea. Moreover, the use of appetite stimulants can be considered.
Renal diets are high in energy density to promote energy intake even with an inconsistent or poor appetite. In these cases, dry foods are helpful, since they are more energy-dense than canned.
Patients that are losing weight due to a poor appetite might need assisted feeding via feeding tubes that can also be used for hydration and to medicate the patient.
1. Ross SJ, Osborne CA, Kirk CA, Lowry SR, Koehler LA, Polzin DJ. Clinical evaluation of dietary modification for treatment of spontaneous chronic kidney disease in cats. J Am Vet Med Assoc. 2006;229(6):949–957.
2. Jacob F, Polzin DJ, Osborne CA, et al. Clinical evaluation of dietary modification for treatment of spontaneous chronic renal failure in dogs. J Am Vet Med Assoc. 2002;220(8):1163–1170.
3. Elliott DA. Nutritional management of chronic renal disease in dogs and cats. Vet Clin North Am Small Anim Pract. 2006;36(6):1377–1384.
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5. Segev G, Fascetti AJ, Weeth LP, Cowgill LD. Correction of hyperkalemia in dogs with chronic kidney disease consuming commercial renal therapeutic diets by a potassium-reduced home-prepared diet. J Vet Intern Med. 2010;24(3):546–550.
6. National Research Council. Nutrient Requirements of Dogs and Cats. Washington, DC: The National Academies Press; 2006.
7. Brown SA, Brown CA, Crowell WA, et al. Beneficial effects of chronic administration of dietary omega-3 polyunsaturated fatty acids in dogs with renal insufficiency. J Lab Clin Med. 1998;131(5):447–455.
8. Plantinga EA, Everts H, Kastelein AM, Beynen AC. Retrospective study of the survival of cats with acquired chronic renal insufficiency offered different commercial diets. Vet Rec. 2005;13;157(7):185–187.