Nutrition for chronic kidney disease in dogs and cats
Friday, October 27, 2017
Renal insufficiency is the most common disease affecting the kidneys of dogs and cats, and unfortunately, is also a common cause of illness and death in pets.
The kidneys are involved in maintaining overall body homeostasis, and as such, have numerous important functions. These include filtering blood through the excretion of metabolic waste, regulating blood pressure, maintaining correct levels of solutes in the blood and controlling pH through acid-base status.
Renal insufficiency is irreversible damage to the kidneys, resulting in a gradual loss of kidney function. A 70 percent or greater loss in kidney function is typically required before pets start to exhibit any symptoms of the disease. This is because of the kidneys' incredible ability to compensate for any functional tissue loss or damage.
The initial cause of damage or injury to the kidneys leading to chronic disease is often unknown, as the underlying cause is usually no longer present by the time the disease is diagnosed. Potential causes include infection, trauma, decreased blood flow to the kidneys and exposure to toxins.
Common signs of renal insufficiency include increased thirst (polydipsia) and urination (polyuria), diarrhea, vomiting, lack of appetite and reduced energy. Loss of body weight and muscle mass are also common, as many pets will also develop anorexia or nausea. Renal insufficiency most often occurs in older pets, but it can affect cats and dogs of any age.
What happens after your pet has been diagnosed with chronic kidney disease? Unfortunately, the disease is irreversible and there is no cure. However, the good news is that it can be well managed through diet and medication.
The International Renal Interest Society (IRIS) has established guidelines for the management of renal insufficiency in dogs and cats. These guidelines follow a staging system that classifies renal insufficiency into one of four stages, based on the magnitude of renal dysfunction. Each stage provides treatment recommendations to help manage symptoms, improve quality of life and increase lifespan.
Nutrition management of renal insufficiency
Nutritional therapy is considered a key component in managing dogs and cats with chronic kidney disease. The IRIS guidelines recommend starting nutritional management of the disease starting in stage 2. Numerous studies have shown an improvement in the quality of life and an increased life span in pets being fed a diet formulated to manage renal disease.
The goals of nutritional intervention are to meet the animal's energy and nutrient requirements, while mitigating clinical symptoms and slowing progression of the disease. Diets suitable for pets with renal insufficiency are available commercially, or a homemade diet formulated by a qualified veterinary nutritionist may be used.
Compared to adult maintenance recipes, diets formulated for the management of renal disease typically contain less protein and phosphorus, while having an increased level of omega-3 fatty acids.
When protein is consumed in excess of the body's requirements, it is broken down into nitrogenous metabolites (urea and creatinine) and filtered out as waste in the urine. Many of the clinical signs of later stage renal insufficiency, such as vomiting and lack of appetite, result from of a build-up of these end products.
An accumulation of nitrogen in the blood, also known as azotemia, is a result of an excess of dietary (exogenous) protein, or an elevation in body (endogenous) protein degradation. Feeding a diet that is restricted in protein allows the kidneys to work less and prevents an accumulation of these waste products.
Studies have shown that modifying dietary protein intake can reduce blood urea nitrogen (BUN) and provide clinical benefits, such as reduction of nausea, for pets with renal insufficiency. Similarly, high-quality protein ingredients that provide all essential amino acids in the amounts pets require are recommended to help reduce the quantity of waste that the kidneys must eliminate.
It is important that pets receive the protein and calories that their bodies require. In the early stages of renal insufficiency, a higher-protein diet may be recommended, particularly for cats, to prevent muscle loss and malnutrition.
If the intake of calories or protein is not high enough, endogenous protein in the body will be broken down and will produce nitrogenous waste products. As a result, an important goal of nutritional therapy and managing chronic kidney disease is to provide the right balance of protein and calories depending on the pet's severity of disease and their symptoms. Dietary protein intake should be adjusted to minimize excess that may result in azotemia, while avoiding excessive restriction that may result in malnutrition.
When the kidneys become damaged, the ability of the kidney to properly filter excess minerals into the urine decreases. This decreased ability results in a higher-than-normal level of phosphorus in the blood, which may lead to the formation of crystals in the kidneys, causing further damage and disease progression.
Phosphorus retention also inhibits the activity of the enzyme responsible for converting inactive vitamin D to active calcitriol, potentially leading to bone loss and vitamin D deficiency.
Diets suitable for renal insufficiency are generally formulated with a lower level of phosphorus to help slow disease progression, improve disease management and increase lifespan. Since foods high in protein are often significant sources of phosphorus, restricting protein and choosing low phosphorus ingredients is generally done in diets used to treat late stage renal insufficiency.
As previously mentioned, it is important to provide pets with enough calories, while providing a restricted level of protein. As such, fat is added to diets for kidney disease to provide pets with a concentrated source of energy and make the food more appealing.
Often, renal therapeutic diets are formulated to be high fat, as this allows the animal to meet its energy requirements from a smaller volume of food.
Omega-3 fatty acids, such as those found in flaxseed, salmon oil and algae extract, are preferred due to their anti-inflammatory benefits and potential to slow disease progression. Additionally, increased survival outcomes have been reported in pets with renal insufficiency receiving larger concentrations of omega-3 fatty acids.
Conversely, high intake of omega-6 fatty acids may have negative consequences for dogs with renal disease by increasing blood pressure within the kidney and resulting in renal injury.
As renal insufficiency is a disease that can change and progress with time, it is important for veterinarians and pet owners to regularly consult regarding optimal dietary management for the pet. Frequent rechecks are crucial for successful long-term management.
Once a diet has been selected, it is important to continue to regularly monitor the pet to make sure the diet is providing optimal nutrition and symptom management.
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