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Cats with IRIS stage 1 and 2 chronic kidney disease maintain body weight and lean muscle mass when fed food having increased caloric density, and enhanced concentrations of carnitine and essential amino acids

Hall JA, Fritsch DA, Jewell DE, Burris PA, Gross KL. Cats with IRIS stage 1 and 2 chronic kidney disease maintain body weight and lean muscle mass when fed food having increased caloric density, and enhanced concentrations of carnitine and essential amino acids. Vet Rec. 2019 Feb 9;184(6):190.

Dietary therapy is the mainstay of management of chronic kidney disease (CKD) is cats. While the role of protein restriction is controversial, there are well known benefits to phosphate restriction, sodium restriction, potassium supplementation, and fatty acid supplementation. Diets formulated for cats with CKD are also alkalinizing, higher in fibre, B complex vitamins, and antioxidants. The role of dietary therapy in IRIS stage 3 and 4 renal disease has been previously well documented. However, the role of dietary therapy in earlier stage CKD is less clear, with some suggesting it may be contraindicated due to insufficient protein levels. There are also a large number of “renal diets’ available commercially, and there has been no direct study demonstrating the benefit of one over another.

The purpose of this study was to determine if renal diets are beneficial to cats with IRIS stage 1 and 2 CKD, and further to determine if a specific renal diet with an increased caloric density, and enhanced concentrations of carnitine and essential amino acids (Hill’s K/D) when compared to an other commonly used renal diet (Royal Canin Renal A). The study was designed as a prospective, double blind, randomized clinical trial (but lacking a negative control group). Cats were recruited from a colony of cats involved in nutrition trials. Animals were neutered, between 2 and 16 years of age, and in general good health with a BCS 2/5 or greater. Cats were enrolled if they were in IRIS stage 1-2 CKD.

Cats were diagnosed with CKD based on an elevated SDMA and one or more of creatinine >1.6mg/dL (140umol/L), abnormal renal palpation, USG <1.035, or UPCR >0.4. Staging was performed according to IRIS guidelines. 57 cats were screened and 28 enrolled. The distribution of cats was as follows:





Med. Age

Completed Study

Control (RC)






Test (Hill’s)






No statistically significant differences in demographic parameters were found between the groups.

Cats were fed either the test (Hill’s k/d) or control (RC Renal A) kibble only diets for a period of 6 months. The amount fo food fed was based on the cat’s RER and previously calculated metabolic rate.  Blood was collected after overnight fasting and urine collected by cystocentesis. Body mass and composition were determined by DEXA analysis.

One cat was dismissed from each group in the first 1-0 days due to palatability issues (93% acceptance rate). One cat was euthanized 27 days into feeding test food due to hypertrophic cardiomyopathy. A second test cat was dismissed after 412 days for HCM and hypertension. 4 cats on control food were dismissed for loss of body condition, loss of appetite, and/or progressive renal disease.

Cats on the control diet voluntarily consumed 64% of calories offered, while cats on the test diet consumed 79% (p=0.05). Cats consuming control food lost a mean of 13% of their body weight compared to baseline (p<0.0001), while cats eating the test food gained 5.8% (p=0.003). There was a similar decrease in body condition score (BCS) of 0.5 in the control group vs no change in the test group (p=0.03 between groups). Control cats lost 11.1% of lean body mass (p<0.0001) while test cats had no change.

Amino acid analysis of both foods was performed to determine  that threonine was the limiting amino acid in both diets. Both diets had a threonine concentration higher than the AAFCO minimum; with test diet 50% higher and control diet 13% higher. Based on daily intakes, 7 of 11 test cats met the minimum requirement for threonine, while no control cats did.

When considering renal biomarkers, there was a significant diet-time interaction only for serum creatinine; which increased in cats fed both control and test foods, but at a faster rate in cats fed control food. Significant increases in calcium, sodium, and phosphorus were also seen in cats fed the control vs test diet.

Overall, cats fed the test diet had worsening biochemical parameters and a greater degree of weight loss, BCS loss, and lean body mass loss when compared to cats fed the test food.

Several potential limitations to this study exist. The study was limited to IRIS stage 1 and 2 cats (and the majority were IRIS 1), and so results may not be translatable to the population of higher stage CKD cats and may primarily apply to stage 1. It is also not clear which individual component or combination of components was the most significant factor in the difference between diets. Only kibbled food was used in this study, however some data suggests that cats with CKD may respond better to a canned diet. Finally, there was no control group present to establish what changes occur in cats fed a “non-renal” diet, and so it is impossible to determine what changes occurred relative to a baseline group. Due to this, the conclusion that renal diets are appropriate in IRIS 1 cats cannot be drawn (as it is possible that cats fed a “normal” diet may have done better or the same as the test population).

Despite some limitations, this study served to demonstrate a benefit in the test diet (Hill’s k/d) over the control diet (Royal Canin Renal A) in cats with early stage CKD over a 6 month period. While further data is needed to determine the effects of these diets in higher stage renal disease and for longer time periods, as well as comparing to other renal diets, this study suggests that the nutritional profile of Hill’s k/d provides a therapeutic advantage to cats in early stage CKD. MK

See Also

Ross SJ, Osborne CA, Kirk CA, et al. Clinical evaluation of dietary modification for treatment of spontaneous chronic kidney disease in cats. J Am Vet Med Assoc 2006;229:949–57.

Scherk MA, Laflamme DP. Controversies in veterinary nephrology: Renal diets are indicated for cats with international renal interest society chronic kidney disease stages 2 to 4: The con view. Vet Clin North Am Small Anim Pract 2016;46:1067–94.

Polzin DJ. Evidence-based step-wise approach to managing chronic kidney disease in dogs and cats. J Vet Emerg Crit Care 2013;23:205–15.