There are a huge range of “clinical” or “prescription” diets on the market. And many of these are aimed at dogs (and cats, for that matter) with kidney problems. But how can they help? Why are they used? And do they actually work, or is it all marketing hype?
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What are kidneys?
The kidneys are two organs found on the left and right sides of a dog’s abdomen that are responsible for filtering blood, removing waste products, and controlling the body’s fluid balance.
Chronic kidney disease (CKD) in dogs is characterised by progressive loss of renal (kidney) function, the prevalence for chronic kidney disease (CKD) in dogs varies widely from about 0.05-3.74%, and even upwards of 25% of dogs in referral centers.
Identified risk factors for chronic kidney disease include:
- Advancing age
- Specific breeds
- Small body size
- Periodontal disease
If your dog has been diagnosed with kidney disease it can be very worrying. Your veterinary team will support you in finding the best management. Part of this management may include a change of diet.
Nutrition in management
Nutrition is arguably one of the most important aspects of chronic kidney disease (CKD) management, alongside other changes. Changing or manipulating your dog’s diet may slow the progression of chronic kidney disease, minimise uraemic symptoms (symptoms associated with abnormally high waste products building up in the blood), and improve quality of life to give you a happier dog for longer.
Did you know that a study in dietary management of chronic kidney disease demonstrated that dogs with the spontaneous form lived an average of 13 months longer when fed a diet designed for renal disease, compared with a maintenance diet? This is one of a number of reasons we may decide to change their diet; to protect the remaining function of these vital organs.
So why do we make the swap?
Dogs eating a renal diet in one study had a reduction in the risk of “uraemic crises” compared with dogs eating the maintenance control diet. A uraemic crisis is a condition where there are abnormally high levels of waste products in the blood due to kidney failure which can make our pets feel extremely unwell. If left untreated this can even be fatal. The delay in development of these uraemic crises and associated mortality rate in dogs fed renal food was thought to be partly associated with reduction in rate of progression of renal failure. This is a real positive as it gives our dogs a better quality of life.
At the end of the study, only 33% of dogs receiving the renal diet died from renal-related causes, compared with 65% of dogs receiving the maintenance diet.
What do they do?
Most therapeutic diets designed for kidney disease use a combination of:
- Moderately restricted protein
- Highly quality/bioavailable proteins
- Restricted Phosphorus
- Restricted Sodium
- Elevated concentrations of omega-3 fatty acids
- Increase in potassium
Most kidney diets will have slightly reduced protein. Protein restriction as a dietary management is sometimes debated.
Some argue that, to retain good muscle mass and increase diet palatability (how tasty it is to pets), dogs with kidney disease should not be placed on a low-protein diet.
However, research shows that overall lower-protein diets, in combination with other nutrient modifications, reduce morbidity and prolong lifespan. So, we need a tasty, lower protein diet…
When looking at protein content of a diet and wondering if it will affect muscle mass, it is important to remember that animals require amino acids rather than protein. So actually, feeding very high-quality protein sources (but in smaller quantities) can lower dietary protein content while preventing protein malnutrition as long as the diet is well-balanced with other essential amino acids. This is what is meant by “high quality” protein sources.
We just need it tasty enough that our pets will eat it. Kidney disease can make our pets feel sick or nauseous; so we need to ensure they don’t get a food aversion to the diet.
What is a food aversion?
Although food manufacturers making renal diets do extremely well at making them highly palatable, as renal failure progresses, animals tend to eat less and may feel sick. This is similar to us eating something with a hangover, feeling really ill and never wanting to touch it again… If the food reminds the dog of feeling very nauseous then they may stop eating it and develop a ‘food aversion’.
It is important to minimise food aversion as much as possible by avoiding renal diets when your dog is particularly nauseous, sick or stressed. This may mean that your veterinary team may NOT feed this diet if your pet is hospitalised with them so that they are more likely to eat this diet when they go home.
As a dog becomes more averse to eating as the disease progresses, it may be necessary to try different flavors or brands or to have a homemade diet formulated by a nutritionist. Remember to not attempt this on your own. It is very difficult to formulate a properly balanced diet for a healthy dog; let alone one with a serious health issue. See our blog on this, Are home-prepared diets for dogs safe? for more detail.
Why low phosphorus?
As the kidneys retain phosphorus, a gland called the parathyroid gland is stimulated to release a hormone to increase the loss of phosphorus via the kidneys.
However, this hormone also stimulates the release of phosphorus from bone. This means patients with kidney issues can get high phosphorus in the blood; and their bones may become weak and even rubbery!
Studies have shown that reducing phosphorus in the diet reduces the level of phosphorus in the blood. The importance of which was demonstrated in a study in which dogs with induced kidney disease were fed a diet with and without phosphorus restriction over 2 years. Dogs on the high-phosphorus diet had a lower survival rate than the restricted-phosphorus group.
Dogs with chronic kidney disease should eat low-sodium diets to reduce the risk of hypertension (high blood pressure) or to lower already high blood pressure.
Why increased omega-3-fatty acids?
Omega-3 fatty acids help minimise glomerular hypertension (high blood pressure) and help support natural anti-inflammatory processes. A Glomerulus is a cluster of nerve endings and small blood vessels and there are many within each kidney. High blood pressure here can cause damage.
Omega-3 fatty acids can inhibit or lessen the formation of proinflammatory chemicals (chemicals that increase inflammation in the body) which helps with anti-inflammatory process.
Diets high in omega-3 fatty acids have been shown to reduce the pressure in the glomerular capillaries (the tiny capillaries in the kidney used for filtering the blood) and to slow down the decline of glomerular filtration rate in some studies.
Overall, it is fairly clear that after a diagnosis of kidney disease a change in diet may certainly be sensible if we want to try and reduce kidney related illness and increase quality of life.