Updated: Feb 19, 2020
This month I wanted to talk about nutritional management of two diseases that we see very commonly. A 9-year-old female spayed Dachshund was referred to us for a nutrition consult, as the referring veterinarian had correctly decided that there was no commercial therapeutic diet (available in Australia) to suit this patient's needs.
Commercial renal diets are too high in fat, and low fat gastrointestinal diets are too high in phosphorus (and potentially protein). The owner had a preference to use turkey in one of the recipes, and also mentioned that the dog really enjoyed different kinds of fish. The nutritional goals for this patient were, therefore, to create a low fat, moderate to low protein, phosphorus-restricted diet, enriched with mixed fermentable fibre, antioxidants, and omega-3 fatty acids.
Unfortunately, it can be a challenge to create highly palatable recipes when both fat and
protein restriction are required. By necessity, these recipes contain mostly carbohydrate.
It is therefore important that for these cases, we make sure that the carbohydrate component of the diet is as tasty as possible. Sometimes we do this by using vegetables like sweet potato and pumpkin, and sometimes we add some homemade broth to the recipes, to add as much flavour as possible.
Phosphorus restriction is an uncontroversial goal for all renal diets, for both dogs and cats. Phosphate retention is the initiating factor for the development of many of the complications observed in chronic kidney disease, such secondary renal hyperparathyroidism, and bone and cardiovascular diseases. Many studies have demonstrated that dietary phosphorus restriction slows decline in renal function and increases mean survival time in dogs (and cats) with chronic kidney disease.
Protein restriction is a more debated goal, and will the sole topic of an upcoming blog post. To summarise, there are three main reasons why restriction of dietary protein for renal patients is recommended:
1) Protein-rich ingredients are a source of non-protein nitrogenous compounds such as urea, which may advance the onset of uraemia.
2) Feeding excessive protein can decrease its digestibility. This may increase fermentation of protein by gastrointestinal microflora. End-products of bacterial protein fermentation include uraemic toxins like p-cresyl sulfate and indoxyl sulfate, which can worsen renal toxicity by increasing oxidative stress and accelerating skeletal muscle atrophy.
The paper by Fernandez-Prado et al. (2017), "Nutrients Turned into Toxins: Microbiota Modulation of Nutrient Properties in Chronic Kidney Disease" provides an excellent overview of this topic.
3) Proteinuria has been shown to have a highly detrimental effect on the kidney. Protein overload of tubular epithelial cells and intrarenal activation of complement can cause infiltration of inflammatory cells and injury to the surrounding interstitial cells, leading to the development of glomerulosclerosis. Excessive albuminuria may also lead to increased renal oxidative stress, which can cause progressive nephron damage. Many studies have demonstrated that decreasing the magnitude of proteinuria by reducing dietary protein intake slows down the progression of nephron loss.
Fat restriction for dogs with a history of pancreatitis is another controversial topic. There is a lack of convincing research on the relationship between dietary fat and pancreatitis in dogs; important precipitating factors may include hypertriglyceridaemia, obesity or a sudden increase in dietary fat. Given the absence of evidence, we typically opt for a conservative amount of dietary fat. However, we try to avoid very severe fat restriction, given that dietary fat increases the energy density of the meals and often improves palatability (which can be vital for patients with a poor appetite). It may be the case that occasional feeding of high fat treats or snacks is a much more critical risk factor, so we recommended that the owners of this dog strictly adhere to the recipes.
The remaining three goals for this patient were enrichment of the diet with fermentable fibre, omega-3 fatty acids, and antioxidants. Supplementation with omega-3 fatty acids has been shown to lower glomerular capillary pressure, reduce proteinuria and slow decline in glomerular filtration rate. Fish oil is often the best thing to add to the diet to provide EPA and DHA; in this case, it was important to use a very concentrated product, to provide maximum enrichment with omega-3 fatty acids, but minimal excessive fat.
Fermentable fibre is also desirable in renal diets. Both animals and humans with chronic kidney disease often exhibit changes in the gut microbiota and increased gut permeability, which may be due to excessive luminal urea and its breakdown product, ammonia, reducing epithelial tight junction proteins in the colon. Dietary supplementation of fermentable fibres like wheat dextrin has been shown to decrease colonic pH and improve gut barrier function, which may reduce translocation of harmful bacterial products and metabolites, decreasing inflammation in the kidneys.
Finally, we typically try to include a range of different vegetables and sometimes a vitamin E supplement, to enrich the diet with vitamin C, vitamin E, beta-carotene and alpha-lipoic acid. Several studies have demonstrated that addition of dietary antioxidants reduces the magnitude of renal glomerulosclerosis and interstitial fibrosis, regardless of dietary polyunsaturated fatty acid ratio.
Phew. Lots of goals to consider. For this dog, we formulated two recipes - one was a turkey and white rice based recipe with additional vegetables like cabbage, kale and broccoli. The second recipe contained canned tuna and salmon, with rice, carrot, red capsicum and pumpkin. To these recipes we also added the required supplements to produce a balanced diet (with the exception of phosphorus restriction), and to achieve the goals described above. The owner transitioned the dog on to the new diet very gradually, to minimise the risk of gastrointestinal upset, and so far, the recipes have been a big success. As this dog's renal disease progresses we will aim to further reduce phosphorus and protein, while still maintaining palatability and food intake. A delicate balancing act!
If you would like to try a homemade diet for your dog or cat with renal disease and/or pancreatitis, please contact us: firstname.lastname@example.org
Read the full paper by Fernandez-Prado et al. here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5452219/