Chronic Kidney Disease (CKD) is a prevalent and increasingly common condition affecting the UK’s cat population, particularly older felines. Estimates suggest that CKD impacts a significant portion of cats over 10 years old and an even higher percentage of those over 15. The kidneys are essential organs, functioning as the body’s primary filtration system. They are responsible for removing toxins from the blood, regulating blood pressure, maintaining fluid balance, and controlling vital mineral and pH levels. The functional units of the kidney, known as nephrons, are finite. As the number of functioning nephrons decreases, kidney function deteriorates, leading to reduced blood filtration and the buildup of waste products, a condition called azotaemia.
Understanding the difference between acute and chronic kidney disease is crucial for proper management. Acute Kidney Disease (AKD) is a short-term condition with a rapid onset of symptoms, potentially treatable with timely medical and nutritional intervention. Triggers for AKD can include reduced blood flow, ingestion of toxins like antifreeze or raisins, or consumption of toxic foods such as onions. In contrast, Chronic Kidney Disease (CKD) is a progressive illness where kidney function gradually declines over time. While CKD is generally irreversible, its progression can be managed and slowed with appropriate care.
Stages of Chronic Kidney Disease
CKD is typically classified into four progressive stages, with cats often not showing physical symptoms until they have lost a substantial amount of renal function, usually by stage III or IV.
- Stage I: Kidney damage begins, but elevated waste products are not yet detectable in the blood. Typically, there are no symptoms.
- Stage II: Waste filtration continues to decline, with elevated waste products in both blood and urine. Physical symptoms are usually absent.
- Stage III: Further decline in waste filtration leads to significantly elevated waste products. Symptoms such as excessive thirst and urination may begin to present.
- Stage IV: Severe decline in kidney filtration causes toxins to build up in the blood, leading to a myriad of physical symptoms including weight loss, vomiting, diarrhea, and lethargy.
Dietary Management for Cats with CKD
Providing an appropriate diet is paramount for cats diagnosed with kidney disease. While many veterinarians recommend specific “prescription” kidney diets formulated with altered protein, phosphorus, and sodium levels, CKD can also be managed successfully with a carefully prepared raw diet, provided certain nutritional criteria are met. Key considerations for managing CKD through diet include protein, phosphorus, moisture, and fat content.
Protein Considerations
Cats are obligate carnivores, naturally selecting diets rich in protein and moderate in fat, with very low carbohydrate content. Their natural prey consists of approximately 54% protein, 45% fat, and 1% carbohydrate. Protein quality is determined by the amino acid profile, digestibility, and bioavailability, which are typically higher in animal-derived sources. For cats with CKD, feeding highly digestible, quality animal protein is essential.
The role of protein restriction in managing CKD in cats is a topic of ongoing discussion. Unlike dogs with advanced CKD, where high urine protein and creatine levels are common, this is less frequently observed in cats, and protein restriction has not been conclusively shown to slow disease progression. In fact, insufficient protein can lead to detrimental weight loss and negatively impact overall health. Cats are metabolically adapted to derive energy from meat, and this requirement does not change with kidney disease. Restricting protein in an obligate carnivore’s diet can cause muscle and organ wastage, as cats cannot effectively downregulate the hepatic enzymes involved in protein metabolism, making them vulnerable to malnutrition.
Protein itself does not damage the kidneys; rather, the waste products generated from protein digestion can accumulate in the blood. In late-stage CKD, moderate protein restriction may help reduce nitrogenous waste and manage proteinuria, but very low-protein diets are generally not advised. Research indicates that cats with CKD might actually require more protein than typically found in “prescription” diets to prevent muscle loss.
The quality of protein significantly influences digestibility and the amount of waste produced, which the kidneys must filter. Higher quality protein results in less nitrogenous waste. For instance, eggs and raw meat are considered top-quality protein sources for cats. Consequently, a cat with kidney issues can consume a larger quantity of high-quality protein without generating as much waste compared to lower-quality protein. Raw animal protein is particularly suitable as it produces less nitrogenous waste than processed proteins that are more challenging to digest.
Phosphorus Management
Phosphorus is a vital mineral for numerous bodily functions, including DNA and RNA synthesis, cell membrane integrity, and energy production (ATP). The body maintains phosphorus levels through intestinal absorption and kidney excretion. When kidney function is compromised, phosphorus can accumulate in the blood. Therefore, a lower phosphorus diet is recommended for cats with CKD to reduce the workload on the kidneys. Phosphate binders, such as calcium carbonate, can be used in conjunction with diet to further reduce phosphorus absorption by binding it in the food, offering greater feeding flexibility. It is advisable to consult your veterinarian to discuss your cat’s specific dietary options.
It is also important to distinguish between different forms of phosphorus. Inorganic phosphorus poses a greater risk than organic phosphorus because it is absorbed more readily into the bloodstream, increasing the burden on the kidneys for excretion. Organic phosphorus is typically water-soluble and found naturally in raw animal and plant ingredients. Conversely, inorganic phosphorus is often added during food processing to meet nutritional requirements. Studies suggest that dietary phosphorus from natural food sources, such as meat and vegetables, does not significantly impact post-meal plasma phosphorus levels as drastically.
Some low-phosphorus meats include chicken, rabbit, and duck. Medium-phosphorus meats include beef and turkey. Bones, dairy products, and organ meats (especially liver) are considered high in phosphorus, but these can be included in moderation rather than completely avoided. Feeding fattier meats with moderate, high-quality protein can be an effective strategy for managing phosphorus intake.
Hydration and Moisture Content
Maintaining adequate hydration is critical for all cats, and especially for those with kidney disease. Dry diets, which contain less than 10% moisture, place a chronic stress on the kidneys. In contrast, raw or wet diets mimic the natural moisture content of prey (approximately 70%), thereby supporting hydration and kidney health. Cats have a naturally low thirst drive, making dietary moisture intake essential. Increasing dietary moisture content can significantly increase urine volume, reducing kidney strain and supporting urinary tract health.
Fat and Omega Fatty Acids
Inflammation is a contributing factor to the progression of kidney disease. Diets high in carbohydrates and processed fats can elevate omega-6 fatty acid levels, promoting a pro-inflammatory state. Supplementation with omega-3 fatty acids, specifically DHA and EPA, has demonstrated anti-inflammatory and renoprotective effects. Experimental studies indicate that DHA and EPA can reduce proteinuria in cats with late-stage CKD. Occasional supplementation with salmon oil is a practical way to provide omega-3 fatty acids to cats.
Raw Diet Criteria for Cats with CKD
In the early stages of CKD, a complete, fresh raw meat diet is considered an excellent option. As the disease progresses, adjustments may be necessary, such as reducing the phosphorus content. For end-stage CKD, moderating protein intake may also be required.
Palatability is a crucial factor, especially for older cats. Circulating toxins and a diminished sense of smell can lead to a reduced appetite, with inappetence affecting a significant percentage of cats with CKD. Raw diets, with their natural fats and aromas, enhance palatability and can help maintain food intake.
Fresh raw kidney meat is highly nutritious, particularly rich in water-soluble B vitamins, which are often lost due to increased urination in CKD. However, to prevent excessive phosphorus intake, kidney should constitute only 3–5% of the diet.
For cats in advanced stages of CKD, the diet should prioritize moderate amounts of high-quality protein and low phosphorus. This approach helps reduce the kidney’s workload and limits nitrogenous waste, which can exacerbate CKD symptoms.
References
Lucy James, BSc (Hons) Bioveterinary Science
