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Kidney diet- beyond controlled protein

BY DR SARAH ROBSON - JANUARY 23, 2024 - URINARY & KIDNEY

 

A common misconception is that a kidney diet is merely a controlled protein diet. In fact, this is not the case. There are many beneficial characteristics of Hill's Prescription Diet kidney foods such as:

  • Controlled, highly digestible protein- Not only does the controlled protein in a kidney diet minimise the accumulation of nitrogenous waste products in the blood, thus decreasing the workload on the compromised kidneys, it also directly helps to reduce phosphorus levels. 

  • Reduced phosphorus- Reducing phosphorus in the diet helps to slow progression of chronic kidney disease (CKD), as the patient is less likely to develop secondary renal hyperparathyroidism and thus mineralisation of their kidneys.  Mineralisation of the kidneys further damages them, causing CKD to progress. 

  • Reduced sodium- Excess sodium has been shown to lead to progression of CKD in cats.1

  • Increased calorie content- Pets with CKD often have a decreased appetite. It is important they consume sufficient calories to meet their energy requirements and preserve their lean muscle mass. Kidney diets are often high in fat which makes the diet energy dense meaning that a patient doesn’t have to eat as much to meet their daily energy requirements, even in the face of a reduced appetite. 

  • Increased omega 3 fatty acids- Helps to decrease inflammatory mediators and reduce the blood pressure in the kidney, thereby helping to slow ongoing damage.2

  • Potassium supplemented- This is particularly important in cats as they are prone to developing hypokalaemia, which can cause generalised muscle weakness.

  • B complex vitamin supplemented- Important for energy metabolism, but are often low in patients with CKD. This is because B complex vitamins are excreted in urine and also lost through vomiting, which can occur in patients with advanced CKD. 

  • Increased antioxidants- Increased free radical damage may contribute to progression of CKD. Added antioxidants have shown benefits in cats and dogs with CKD.3,4

  • Added soluble fibre- Can indirectly lower blood urea nitrogen (BUN) through increased faecal excretion of nitrogenous waste. 

  • Neutral to alkalinising- Helps to reduce metabolic acidosis and the associated clinical signs.

  • L-Carnitine- Helps improve utilization of fat to avoid muscle breakdown for energy. It is also protective against cachexia.

  • Enhanced Appetite Trigger (EAT) technology- EAT is used in Hill’s Prescription Diet k/d dry foods and uses key aromas, taste profiles and flavours to stimulate appetite in pets with CKD and encourage food intake.

  • Activbiome+ Kidney Defense- 3 components which have been added to all k/d products:

  1. Betaine - A nutrient with antioxidant and anti-inflammatory properties that functions as an osmolyte to support cell hydration
  2. Oat beta-glucan - Soluble, complex fibre that modulates the microbiome (distal colon) and helps reduce uraemic toxins produced by gut bacteria
  3. FOS (fructo-oligosaccharides) - Soluble, simple fibre that modulates the microbiome (proximal colon) and helps reduce uraemic toxins produced by gut bacteria

Let’s look at the current evidence

The jury is out on when to start a controlled protein diet- after all, high quality protein is still very important to maintain muscle mass in chronic kidney disease (CKD) patients.  There is grade 1 evidence to show we should be implementing a kidney diet in stage 2 disease or higher in cats, and in stage 3 disease or higher in dogs.1 The International Renal Interest Society (IRIS) also recommends a reduction in phosphorus intake in order to maintain a plasma phosphate concentration between 0.9-1.5mmol/l, in which case a kidney diet could also be beneficial in this stage.2  

The nutrition of k/d has been shown to improve and lengthen quality of life in both cats and dogs with CKD.3,4

The indication to feed a kidney diet to dogs is also influenced by the presence of proteinuria (in the absence of an active sediment) with a urine protein creatinine ratio (UPC) >0.5.2 In dogs that have proteinuria, underlying diseases need to be ruled out or managed. If the proteinuria is persistent, then these patients will also benefit from a kidney diet. Whilst it might seem counterintuitive to put a patient with proteinuria on a lower protein diet, proteinuria in itself is nephrotoxic, so minimising this is going to be important for long term outcome.

 

The IRIS guidelines have been updated to include symmetric dimethylarginine (SDMA) ranges for each stage of kidney disease. This test can help to identify kidney disease earlier than creatinine. Like any test it should be interpreted in conjunction with other laboratory results. The important thing to remember about SDMA is it is correlated with glomerular filtration rate (GFR). This means that if it is elevated you must rule out pre-renal (and post-renal) causes for this, such as dehydration. Click here to check out the IRIS guidelines.

What about IRIS Stage 1?

You may be wondering what to feed a patient with IRIS stage 1 CKD. I recommend ensuring they are on an age appropriate diet with controlled levels of sodium and phosphorus. Any of the Hill’s Science Diet Adult 7+ and 11+ diets are suitable options. If you know a particularly fussy pet then it may be worth considering transitioning them to a kidney diet even in stage 1. This is because it is much easier to get a patient onto a new diet when they are feeling well versus once they become uraemic and start feeling sick. In a study of 36 dogs with IRIS stage 1 kidney disease, 97% successfully transitioned onto k/d canine and ate the diet for the 1 year duration of the study.5

So what exactly are we hoping to achieve when we transition a patient to a kidney diet?

Therapeutic kidney food is the only therapy shown to improve and lengthen quality of life in both cats and dogs with CKD.3,4There are 4 main goals of nutritional management including:

  • Control signs of uraemia
  • Maintain adequate fluid, electrolyte and acid base balance
  • Provide adequate nutrition to meet energy needs and maintain lean muscle mass
  • Minimise progression of disease

What is the best way to get the pet to accept the new kidney diet?

  1. Transition– It takes the gastrointestinal tract several days to adapt to a new food. For this reason we recommend a minimum transition of 7 days by slowly decreasing the portion of the old food and gradually increasing the portion of the new food. In particularly fussy pets I advise a transition of 2-4 weeks but in the occasional pet it may take 6-8 weeks! 
  2. Establish realistic client expectations- this is the most important tip. If a client expects a transition will take 6-8 weeks they are less likely to give up when Fluffy won’t eat the food on the first day.
  3. Start Early– It is much easier to get a patient onto a new diet when they are feeling well.
  4. Avoid food aversions– Don’t introduce k/d to a patient whilst they are in hospital. It is instead preferable to offer a wet mature adult variety food such as whilst they are in hospital. It is imperative that nausea is controlled before offering any food. Some cats need encouragement to eat; patting or gently stroking them as well as feeding them in a quiet room or up high so they feel safe can help encourage them to eat.
  5. Presentation– Cat’s like to be fussy and like us, they care about how their food is presented. Some cats get ‘whisker fatigue’ from constant stimulation of their whiskers, so offering food on a flat dish rather than a bowl can help to counteract this issue.  Ensure the bowl is cleaned regularly.
  6. Check for causes of inappetance– In patients with CKD, azotaemia and/or oral discomfort are common reasons for a pet to go off its food. Remember to look for an underlying cause of inappetance prior to labelling the food as unpalatable.

For tips on feeding the cat with CKD why not check out our blog on ‘Important considerations when it comes to feeding kidney cats’.

Dr Annabel Robertson BVSc (Hons) MANZCVSc MBA, Hills Technical Services Veterinarian

Dr Sarah Robson graduated with honours from the University of Melbourne in 2009 and went on to work in small animal practice. She then returned to U-Vet in 2012 to complete a clinical pharmacology residency and become a lecturer and general practice veterinarian in the busy teaching hospital. Sarah is a member of the Australian and New Zealand College of Veterinary Scientists in pharmacology and has completed a masters thesis investigating antibiotic resistance. Sarah joined Hill’s Pet Nutrition in 2021 as the Professional Consulting Veterinarian for Victoria and Tasmania.

References:

  1. Roudebush P, Polzin DJ, Adams LG et al. An evidence-based review of therapies for canine chronic kidney disease. J Small Anim Pract 2010; 51:244-252.
  2. International Renal Interest Society. Iris staging of CKD. Available at www.iris-kidney.com
  3. 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;229:949–957.
  4. Jacob F, Polzin DJ, Osborne CA et al. Clinical evaluation of dietary modification for treatment of spontaneous chronic kidney disease in dogs. J Am Vet Med Assoc 2002;220:1163-1170.
  5. Hall JA, Fritsch DA, Yerramilli M et al. A longitudinal study on the acceptance and effects of a therapeutic renal food in pet dogs with IRIS-Stage 1 chronic kidney disease. J Anim Physiol Anim Nutr. 2017;102:1-11.
  6. Kirk CA, Jewell DE, Lowry SR. Effects of sodium chloride on selected parameters in cats. Vet Ther 2006;7:333-346.
  7. Elliott DA. Nutritional management of chronic renal disease in dogs and cats. Vet Clin N Am Small Anim Pract 2006;36:1377-1384.
  8. Yu S, Paetau-Robinson I. Dietary supplements of vitamins E, C and beta-carotene reduce oxidative stress in cats with renal insufficiency. Vet Res Comm 2006;30:403-413.
  9. Yu S, Gross KL, Allen TA. A renal food supplemented with vitamins E, C and beta-carotene reduces oxidative stress and improves kidney function in client-owned dogs with stages 2 or 3 kidney disease. J Vet Intern Med 2006;20:1537.

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