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YOU HAVE ASKED...

What dietary changes should be considered (and when) for a patient diagnosed with chronic kidney disease (CKD) based on blood, urine, and symmetric dimethylarginine (SDMA) results?  

THE EXPERTS SAY...

The advent of the SDMA biomarker (IDEXX.com) has enabled earlier diagnosis of CKD in cats and dogs when performed with serum creatinine, blood urea nitrogen, and urinalysis.1,2 The International Renal Interest Society (IRIS) offers peer-reviewed resources that allow for specific and practical classification of a patient’s CKD stage.3 These guidelines use serum creatinine values and recently updated modifications if SDMA values are known for early CKD stages. Based on IRIS staging of CKD, recommendations for additional diagnostics, therapy (nutrition and drug), and prognosis are provided for each stage. Although it is unclear which therapeutic interventions are most impactful in the early IRIS stages of CKD, there is sufficient evidence that appropriate changes to a patient’s diet can reduce morbidity and may increase longevity.4-6 

Nutritional and medical therapy for CKD should be determined and further individualized by:

  • IRIS CKD stage and substage, as well as SDMA values (if known)
  • Consideration of concurrent medical concerns that affect quality of life and that may limit nutritional options (eg, concurrent dermatologic or GI disease, fat intolerance, obesity or muscle loss management, endocrine disease)
  • Assessment of CKD nutrients of concern (ie, protein, phosphorus, sodium, potassium, eicosapentaenoic acid [EPA], docosahexaenoic acid [DHA]) in current diet to determine how these key nutritional factors align with nutrition recommendations for renal disease stage. (Of note, diet refers to everything consumed and includes all foods, treats, and water.)
  • Clinician evaluation of owner priorities and capability of ongoing monitoring for eventual CKD progression, as well as taste and texture preferences, to optimize acceptance and diet transition success

Related Articles
Laboratory Evaluation in Dogs & Cats with Chronic Kidney Disease
Diets for Each Life Stage

Nutrients of concern are defined by nutritionists as key dietary nutrients known to have specific associations (positive or negative, direct or indirect) on clinical outcome. Although all nutrients in diet are important and play a role, in certain medical conditions specific nutrients should be considered, assessed, and potentially adjusted to maximize dietary benefit. 

Dietary nutrients of concern in order of importance for all stages of CKD include:

  • Phosphorus: CKD has been associated with hyperphosphatemia and hyperparathyroidism and is clinically related to rate of CKD progression7,8
  • Total Protein (Nitrogen): Has been associated with uremia, metabolic acidosis, glomerular hyperfiltration and hypertension, proteinuria, and hypoproteinemia  
  • Sodium: Adjustment may help in managing hypertension, if present.
  • Potassium: CKD patients may be hypo-, normo-, or hyperkalemic. Levels of potassium in the diet should be adjusted on an individual basis.
  • Omega-3 Constituents (EPA and DHA): These specific fatty acid components (unique to omega-3) are considered renal protective and are associated with increased survival times.9,10

IRIS Stage 1 or 2

There is no published consensus and a scarcity of scientific literature on the proper diet for patients with significantly increased SDMA values within IRIS stage 1 CKD. Despite this, the authors believe consideration of nutrients of concern in the current diet and initiation of owner discussion regarding dietary changes should begin with recognition of this CKD stage. 

A review of the current diet is prudent, particularly when patients are fed over-the-counter products, as these can be excessively high in nutrients relative to requirements for animals. This is typically done for palatability and marketing reasons. There are no Association of American Feed Control Officials (AAFCO)11 maximums on protein, sodium, or potassium in pet foods, and the allowed maximum on phosphorous is 5 times the National Research Council’s (NRC’s) adequate intake values.12 

The authors suggest that if levels of nutrients of concern in the current diet are excessive—and because chronic renal disease is always progressive (and phosphrous intake appears directly related to the rate of CKD progression)—it is sensible and does not harm the patient to transition to a diet closer to AAFCO minimums. AAFCO minimums are lower limits on the food product and should not be mistaken for minimum animal requirements. It is important to recognize that a patient eating a diet consisting of nutrients of concern at or close to AAFCO lower limits will unlikely benefit from diet transition, further proving the need for assessment of the current diet. 

For patients with IRIS stage 2 CKD, recommendation of a “kidney” or “kidney-friendly” diet may (or may not) be indicated or beneficial for the patient. This is because dietary descriptors such as renal, kidney, supportive, or protective are neither nutritionally nor officially defined terms. No nutrient profile is appropriate for all renal patients (or all IRIS stages), and each manufacturer decides independently on the nutrient profile of products intended and marketed for animals with CKD (Tables 1 & 2).

Table 1
Feline Renal Diets Relative to NRC & AAFCO Values (SORTED BY PHOSPHOROUS LEVEL)*
 Phos mg/McalProtein g/McalSodium mg/McalPotassium mg/Mcal
NRC 2006 minimum requirement for adult maintenance**350401601300
NRC 2006 recommended allowance for adult maintenance‡640501701300
Royal Canin Veterinary Diet Renal Support D (canned)800639001900
Hill’s Pet Nutrition k/d Feline with Chicken (canned)850656802640
Royal Canin Veterinary Diet Renal Support E (canned)900665001900
Royal Canin Veterinary Diet Renal Support S (dry)10005810002100
Royal Canin Veterinary Diet Renal Support T (canned)10006310001900
Hill’s Pet Nutrition k/d Feline Chicken & Vegetable Stew (canned)1050655302310
Hill’s Pet Nutrition k/d Feline Vegetable & Tuna Stew (canned)1070675302450
Royal Canin Veterinary Diet Renal Support A (dry)1100599002300
Nestle Purina Veterinary Diets NF Kidney Function (dry)1100663002100
Royal Canin Veterinary Diet Renal Support F (dry)11006610002300
Hill’s Pet Nutrition k/d Feline with Ocean Fish (dry)1130666502000
Hill’s Pet Nutrition k/d Feline with Ocean Fish (canned)1170665002410
Nestle Purina Veterinary Diets NF Kidney Function (canned)1200724002500
Hill’s Pet Nutrition g/d (canned)1230827601710
AAFCO 2016 minimum for adult maintenance1250655001500
Rayne Clinical Nutrition Adult Health RSS (canned)126012516801830
Hill’s Pet Nutrition k/d Feline with Chicken (dry)1290665201630
Hill’s Pet Nutrition g/d (dry)1350797201840

*Values obtained from company websites at time of publication
**Minimum requirement is minimum amount of a bioavailable nutrient.
‡Recommended allowance is minimum requirement plus a bioavailability factor when applicable.

Consider This: Veterinary therapeutic diets suggested for managing CKD range 1.7-fold in phosphorous (800-1350 mg/Mcal) for cats and 2.3-fold (480-1100 mg/Mcal) for dogs.

Because CKD is progressive, the authors suggest that nutrients of concern in the current diet be evaluated and IRIS stage 2 CKD patients be transitioned onto a veterinary therapeutic diet with nutrient concentrations closer to NRC maintenance allowance levels. Results of clinical trials support the benefit of feeding a phosphorous-reduced or protein- and-phosphorous-reduced diet to cats and dogs with IRIS stages 2 and 3 to minimize uremic episodes and increase longevity.4-6,10

IRIS Stage 3 or 4

For patients with IRIS CKD stages 3 and 4, it can be challenging to determine which dietary components are driving the benefit noted in renal diet trials (eg, phosphorus alone or protein, phosphorus, and calories synergistically).13 Amid this uncertainty (and often controversy), there is consensus that there is no renal diet that is best for every feline or canine CKD patient or every IRIS stage or substage. However, there are multiple nutritional options with differing nutrient profiles available. Selection for patients with stages 3 and 4 CKD should be based on individual patient needs for specific nutrients of concern. 

Consider This: Not every renal patient requires a low-sodium or potassium renal diet.

The nutritional strategy for later IRIS stages of CKD would ideally adjust nutrients of concern as needed after patient assessment in the following order of importance:

  • Decreased dietary phosphorus before hyperphosphatemia warrants pharmacologic therapy 
  • Decreased dietary protein when BUN begins hindering or reducing appetite 
  • Adjusted protein amount and quality with hypoproteinemia due to proteinuria to balance between lowest BUN and highest serum protein levels
  • Decreased sodium if arterial blood pressure warrants use of pharmacologic therapy
  • Adjusted potassium only as needed based on patient serum levels
  • EPA and DHA (50-100 mg/kg) only if altered palatability due to EPA/DHA intake does not decrease overall food intake 

None of the commonly available renal-labelled diets contain less than the NRC recommended daily allowance of protein (cats, 50 g/Mcal; dogs, 25 g/Mcal; see Tables 1 & 2); however, these products differ substantially in protein, phosphorus, sodium, potassium content, and ingredient composition (ie, flavor, texture, water content). This allows clinicians to select the best possible diet(s) for each patient based on IRIS stage/substaging, potential concurrent disease processes, and owner desires and constraints. 

Table 2
Canine Renal Diets Relative to NRC & AAFCO Values (SORTED BY PHOSPHOROUS LEVEL)*
 Phos mg/McalProtein g/McalSodium mg/McalPotassium mg/Mcal
NRC 2006 minimum requirement for adult maintenance**30020751000
Hill’s Pet Nutrition k/d (canned)48032400810
Royal Canin Veterinary Diet Renal Support A (dry)500359001600
Rayne Clinical Nutrition Restrict – CKD (canned)530435702030
Hill’s Pet Nutrition k/d Canine Beef & Vegetable Stew (wet)590353901690
Royal Canin Veterinary Diet Renal Support S (dry)700319001500
Royal Canin Veterinary Diet Renal Support E (canned)700334001300
Hill’s Pet Nutrition k/d Canine Chicken & Vegetable Stew (canned)710354001920
NRC 2006 recommended allowance for adult maintenance‡750252001000
Hill’s Pet Nutrition k/d Canine with Chicken (dry)750334202040
Hill’s Pet Nutrition k/d Canine with Lamb (dry)750363701720
Nestle Purina Veterinary Diets NF Kidney Function (dry)8003310001800
Royal Canin Veterinary Diet Renal Support F (dry)800349001500
Royal Canin Veterinary Diet Renal Support T (canned)800365001100
Nestle Purina Veterinary Diets NF Kidney Function (canned)800394002300
Royal Canin Veterinary Diet Renal Support D (canned)8004212001800
AAFCO 2016 minimum for adult maintenance1000452001500
Hill’s Pet Nutrition g/d (canned)1050495701910
Hill’s Pet Nutrition g/d (dry)1100465001790

*Values obtained from company websites at time of publication
**Minimum requirement is minimum amount of a bioavailable nutrient.
‡Recommended allowance is minimum requirement plus a bioavailability factor when applicable.

Older patients frequently have concurrent obesity, osteoarthritis, sarcopenia, diabetes, hypo- or hyperthyroidism, pancreatitis, or urolithiasis.14,15 Consideration of concurrent disease(s) should affect diet selection (eg, lower-fat renal product for a patient with concurrent pancreatitis, novel or hydrolyzed protein diet if concurrent dermatologic or GI adverse food reaction). 

Hydration is another dietary consideration in CKD patients. Feeding a wet or canned diet (≈75% water) will provide water intake at or slightly above maintenance fluid requirements when the patient consumes sufficient calories to maintain body weight.

Successful diet transition can be more challenging (especially for cats) as CKD progresses. Some specialists advise transitioning patients with CKD to kidney-labelled products at IRIS stages 1 or 2 when appetite is unaffected.16 In a study of 128 cats with IRIS stages 1 to 3, 93.7% were successfully transitioned to renal food and continued eating it until the last study assessment.17

Conclusion

CKD is progressive in dogs and cats. Adjustment of specific dietary CKD nutrients of concern can decrease morbidity and extend longevity. There is rationale for discussing diet and contemplating nutritional changes in patients with all IRIS CKD stages. When to suggest that change has been debated, particularly with earlier IRIS stages, but because SDMA is an IRIS-accepted predictor of renal damage, and because of the benefits of appropriate diet in managing CKD, suggestion of dietary review and transition (if needed) during stage 1 is advisable. For IRIS stage 2 or higher, thoughtful consideration of the patient’s nutritional needs and specific CKD stage, substage, and other factors are needed when selecting diet. This necessitates attention to the dietary levels of key nutrients of concern for CKD in products marketed as kidney, renal or kidney supportive or renal friendly. 

Of note, products marketed for renal disease are not deficient in protein, phosphorous, or sodium, according to the NRC’s adequate intake values; rather, they more closely approximate animal requirements without being excessive. Thus, these products are safe for long-term feeding when guided by veterinary recommendations.

AAFCO = Association of American Feed Control Officials, BUN = blood urea nitrogen, CKD = chronic kidney disease, DHA = docosahexaenoic acid, EPA = eicosapentaenoic acid, IRIS = International Renal Interest Society, NRC = National Research Council, SDMA = symmetric dimethylarginine

References and author information Show
References
  1. Nabity MD, Lees GE, Boggess MM, et al. Symmetric dimethylarginine assay validation, stability, and evaluation as a marker for the early detection of chronic kidney disease in dogs. J Vet Intern Med. 2015;29(4):1036-1044.
  2. Hall JA, Yerramilli, M, Obare E, Yerramilli M, Jewell DE. Comparison of serum concentrations of symmetric dimethylarginine and creatinine as kidney function biomarkers in cats with chronic kidney disease. J Vet Intern Med. 2014;28(6):1676-1683.
  3. International Renal Interest Society. IRIS staging of CKD. IRIS website. http://www.iris-kidney.com/guidelines/staging.html. Accessed November 2016.
  4. 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.
  5. Elliott J, Rawlings JM, Markwell PJ, Barber PJ. Survival of cats with naturally occurring chronic renal failure: effect of dietary management. J Small Anim Pract. 2000;41(6):235-242.
  6. 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. 
  7. Geddes RF, Finch NC, Syme HM, Elliott J. The role of phosphorus in the pathophysiology of chronic kidney disease. J Vet Emerg Crit Care (San Antonio). 2013;23(2):122-133.
  8. Ross LA, Finco DR, Crowell WA. Effect of dietary phosphorus restriction on the kidneys of cats with reduced renal mass. Am J Vet Res. 1982;43(6):1023-1026.
  9. Brown SA, Brown CA, Crowell WA, et al. Effects of dietary polyunsaturated fatty acid supplementation in early renal insufficiency in dogs. J Lab Clin Med. 2000;135(3): 275-286.
  10. Plantinga EA, Everts H, Kastelein AMC, Beynen AC. Retrospective study of the survival of cats with acquired chronic renal insufficiency offered different commercial diets. Vet Rec. 2005;157(7):185-187. 
  11. Association of American Feed Control Officials. Guidelines for protein, phosphorus, sodium, potassium. AAFCO website. www.aafco.org. Accessed November 2016.
  12. National Research Council. Nutrient Requirements of Dogs and Cats. Washington, DC: National Academies Press; 2006:359-360, 366-367.
  13. Elliot J, Barber PJ. Feline chronic renal failure: clinical findings in 80 cases diagnosed between 1992 and 1995. J Small Anim Pract. 1998;39(2):78-85.
  14. Larsen JA, Farcas A. Nutrition of aging dogs. Vet Clin North Am Small Anim Pract. 2014;44(4):741-759.
  15. Laflamme D, Gunn-Moore D. Nutrition of aging cats. Vet Clin North Am Small Anim Pract. 2014;44(4):761-774.
  16. Sparkes AH, Caney S, Chalhoub S, et al. ISFM consensus guidelines on the diagnosis and management of feline chronic kidney disease. J Feline Med Surg. 2016;18(3):219-239.
  17. Fritsch DA, Jewell DE. Acceptance and effects of a therapeutic renal food in pet cats with chronic kidney disease. Vet Rec Open. 2015;2:e000128. doi:10.1136/vetreco-2015-000128
Authors

Michelle Evason

DVM, DACVIM (SAIM) Rayne Clinical Nutrition

Michelle Evason, DVM, DACVIM (SAIM), is small animal internist. She has previously worked in specialty clinical practice at large private referral centers, in academia as clinical faculty at Tufts University, and in the pet food industry. Her clinical interest focuses on the role of nutrition (and anything else) in improving patient care and aiding owner compliance. In early 2013, she began her own private consultation business.

Rebecca Remillard

DVM, PhD, DACVN Veterinary Nutritional Consultations

Rebecca Remillard, DVM, PhD, DACVN, is founder and president of Veterinary Nutritional Consultations, where she specializes in formulating strategically appropriate dietary recommendations for dogs, cats, and horses with medical conditions. She has been published in several veterinary journals and textbooks and has extensive veterinary teaching experience. Dr. Remillard earned her DVM from Tufts University.

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