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Therapeutic diets for chronic kidney disease are not necessarily equivalent, or are they?


Hall JA, Fritsch DA, Jewell DE, et al. 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. 2018 Dec 4. pii: vetrec-2018-104865.

Nutritional management goals for chronic kidney disease (CKD) in cats are to reduce risk of uremic crisis (ie., severe acid buildup in body), meet the cat’s nutrient and energy requirements, normalize serum phosphorus, maintain hydration and electrolyte balance, and slow the progression of the disease.  Therapeutic kidney diets generally contain less protein, phosphorus, and sodium with increased fat, potassium, omega-3 fatty acids, and buffering capacity.  Although restriction of dietary protein has been demonstrated to slow progression of kidney disease in rats and humans, no definitive studies have been performed in cats, which are obligate carnivores.  Overly restricted proteins may cause protein and amino acid deficiency in CKD cats; on the other hand, avoidance of excessive dietary protein may be necessary to prevent uremic crisis.  Therapeutic kidney diets are considered indicated for cats in International Renal Interest Society (IRIS) Stage 2-4 CKD (ie. serum creatine greater than ~ 1.6mg/dL and urine concentration below ~ 1.035.

Dr. Jean A Hall, College of Veterinary Medicine at Oregon State, Corvallis, Oregon in collaboration with researchers associated with Hill’s Pet Nutrition, Inc. enrolled 28 adult cats with IRIS Stage 1 and 2 CKD and compared two commercially available therapeutic kidney diets in a prospective, randomized, 6-month feeding trial.   Twenty cats completed the study. The goal of this study was to determine whether two different therapeutic kidney diets were appropriate for cats with either IRIS Stage 1 and 2 CKD.  Royal Canin Renal Support A Feline dry was referred to as the control diet and Hill’s Prescription diet k/d Feline with chicken dry was referred to as the test diet.

Palatability of both control and test food was considered good; only one cat in each group was dismissed for poor food consumption. Thus, 93% of cats in each group successfully transitioned onto foods fed in this study. Cats consuming control food had a significant loss of mean body weight (-13%) and a significant reduction in lean body mass (-11.1%) during the 6-month feeding period, whereas cats consuming test food had a significant increase in mean body weight (+5.8%) and no change in lean body mass during the 6-month feeding period.  Cats consumed 23% less calories when fed the control diet compared to cats fed the test diet.

Control and test diets met AAFCO minimum recommendations for adult maintenance.  Both diets have similar protein content, but with different composition.    In addition, test food was enhanced with essential amino acids, L-carnitine, and palatability.  Test diet also had increased caloric density compared to control diet.  Researchers mention another (unpublished) study in which adult cats consuming food supplemented with L-carnitine gained lean body mass over a 6-month feeding period compared with cats fed identical food without carnitine supplement; thus, the reason for increasing L-carnitine content in test diet.

In conclusion, this study suggests that therapeutic renal foods with good palatability, increased caloric density and enhanced concentrations of essential amino acids and L-carnitine may help cats with CKD maintain body weight and lean body mass.  It is further suggested that cats in IRIS Stage 1 CKD would benefit from renal diets with essential amino acid content, higher L-carnitine, and higher energy density.

I would like to point out that Royal Canin Veterinary Diet approach to feeding cats with CKD is different than Hill’s Pet Nutrition; namely, Royal Canin offers various dry diets that have kibbles with different texture, shapes and sizes in order add variety and thereby stimulate decreased appetites.  Thus, this study already had an inherent built in bias benefiting the test diet.  Researchers do state, “if food and caloric consumption were normal based on NRC estimates, both control and test diets should have provided adequate intake of essential amino acids.”  Bottomline, cats eating Renal Support A Feline dry diet could have simply not consumed enough calories.  This could suggest that higher energy dense diet is most important in order to maintain weight and lean muscle mass.

Can you imagine a study wherein Royal Canin Veterinary Diet and Hill’s Pet Nutrition each donated $15,000 (or possibly more) to Winn to fund feline nutrition study(ies); A study (or studies) conducted in academia that are completely impartial to company profit bias that could influence study design.  I would find it useful to know if therapeutic renal canned diets are a better option for CKD cats compared to therapeutic dry diets.  Also, is protein restriction necessary compared to other dietary modifications?  It seems that enhancing diets with more essential amino acids is basically putting the protein back into the diet. Is carnitine really the primary reason for the perceived benefit of Hill’s k/d dry over Royal Canin Renal Support Feline A dry diet in this study?  Or, control cats simply didn’t eat enough calories.  Lastly, does statistical significance truly equate with clinical significance in this study with n= 20. [GO]