Nutritional Management of Chronic Kidney Disease
Nutritional management is a very important part of the medical management of chronic kidney disease (CKD). Several clinical studies have shown that the use of specific diets formulated for the management of CKD both improve quality of life, by reducing the frequency and severity of clinical signs, and survival.1
These diets are restricted in phosphorus, moderate in protein, moderate in sodium, boosted in B vitamins, and are alkalinizing. Depending on the brand (cat or dog), they can be also high or moderate in potassium and include long-chain omega 3 fatty acids. The specific modifications will vary depending on the species of the patient and the stage of kidney disease according to the International Renal Interest Society (IRIS).2
Phosphorus restriction is the most important characteristic, to manage renal secondary hyperparathyroidism. The use of phosphate binders will be necessary at late stages of the disease, where dietary restriction is not enough. Sodium is provided in moderate amounts, but not below requirements, since a truly restricted sodium diet can stimulate the renin angiotensin aldosterone axis and result in hypertension.3 Potassium varies greatly in different diets, and it is important to choose the adequate one, since some renal patients will be hypokalemic (common in cats) but some will be hyperkalemic, especially terminal patients and those receiving ACE inhibitors such as enalapril or benazepril.
Protein should be provided in adequate amounts and be of a high biological value, to avoid creating essential amino acid deficiencies. Renal diets usually provide less protein than maintenance diets to reduce the amount of nitrogenous waste products and thus reduce the incidence of uremia, although it does not seem to help slow down progression.1
B vitamin deficiency can happen due to increased losses via the urine and to reduced intake, secondary to hyporexia. These diets are fortified in these nutrients. Also, CKD patients tend to metabolic acidosis, and these diets alkalinize to try to compensate for this. Over-the-counter diets for cats are almost always acidifying, so they are never a good choice for stage II to IV CKD felines.
Nutritional plan: A nutritional evaluation following the WSAVA guidelines4 should be performed in each patient to decide the best plan.
1. When to Start Dietary Management
Patients with CKD of stages II to III will benefit from a renal diet, ideally chosen to fit the patient and the stage. Some of the canine renal diets are formulated for early stages, and they are more adequate for these cases if available. Patients with stage I do not require a diet change, unless they have proteinuria, where they will benefit from a low-protein diet.
2. What to Feed
Commercial renal diets (from Hill's, Royal Canin, Purina, Iams/Eukanuba) are available in the market and can be chosen depending on availability, palatability, and nutrient characteristics (protein, phosphorus, potassium, EPA+DHA, etc.). Treats, if tolerated, can be given, as long as they provide less than 10% of the total daily calories. They should be low in protein, phosphorus, and salt, so foods like meats, cheese, and preserves should be avoided. Fruits and vegetables (beans, banana, apple, melon, etc.) are excellent options.
3. How Much to Feed
The diet should be fed in sufficient amounts to maintain a stable body weight and ideal body condition score (BCS). Maintenance energy requirements (MER) can be used as a start but will need monthly adjustments. Patients with low BCS can be fed 20% more of their MER. Patients with a high BCS will need to be carefully evaluated and a decision to address the obesity or not should be made based on quality of life.
4. How to Feed
Multiple times a day and ad libitum feeding are both indicated in patients with poor appetite and low BCS. Overweight patients should be fed portion controlled to maintain their BW and prevent further weight gain. 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.
Monitorization is important to adjust the plan: body weight, BCS, bloodwork (BUN, creatinine, albumin, phosphorus, potassium...) and urinalysis (USG, UPC, culture...) are all important to adjust the diet, the amount fed, and the route of administration.
References
1. Elliott DA. Nutritional management of chronic renal disease in dogs and cats. Vet Clin North Am Small Anim Pract. 2006;36:1377–1384.
2. www.iris-kidney.com
3. Buranakarl C, Mathur S, Brown SA. Effects of dietary sodium chloride intake on renal function and blood pressure in cats with normal and reduced renal function. Am J Vet Res. 2004;65(5):620–627.
4. www.wsava.org/nutrition-toolkit