Chronic kidney disease is very common in the UK cat population, with its prevalence ever increasing, particularly in older cats. It’s estimated to affect 30% of cats over 10 years old, and a staggering 80% of cats aged above 15 (1). The kidneys are vital organs which act as the body’s filtration system, keeping the blood clean and free of toxins. They regulate blood pressure, water consumption, pH levels, and minerals such as phosphorous, magnesium, and sodium. The nephron is the functional unit of the kidney, as the number of working nephrons decreases, the symptoms of kidney disease become more severe. A reduction of nephrons subsequently leads to a reduced blood filtration rate, which reduces the ability of the kidneys to filter and excrete waste products efficiently (2). When the kidneys are not functioning correctly, these waste products can build to dangerous levels in the blood, which is known as azotaemia (3).
Acute or Chronic?
| Acute Kidney Disease Symptoms | Chronic Kidney Disease Symptoms |
| Lethargy Diarrhoea Vomiting Disorientation Severe weakness Difficulty urinating | Excessive thirst Excessive urination Reduced appetite Weight loss Urinary infections Vomiting and diarrhoea |
Acute Kidney Disease (AKD)
AKD is typically short term, and often rapidly diagnosed due to its sudden onset of symptoms. Correct medical and nutritional intervention can see cats fully recovered (4). It can be caused by a restriction of blood flow, or due to the ingestion of a toxin (such as antifreeze or rat poison) or eating poisonous foods such as raisins or onions.
Chronic Kidney Disease (CKD)
CKD is a slowly progressing illness, where the kidneys gradually lose function, but may be managed and slowed with the correct care.
There a 4 progressive stages to CKD (5)
| Stage I – Damage begins to occur, but elevated waste products are not yet identifiable in the blood. Typically, no symptoms present. |
| Stage II – Waste filtration continues to decline, elevated waste products in blood and urine. Typically, no physical symptoms present. |
| Stage III – Waste filtration continues to decline, further elevating waste products in blood and urine. Symptoms begin to present as excessive thirst and urination. |
| Stage IV – Severe decline in kidney filtration, causing toxins to build up in the blood. Myriad of physical symptoms including weight loss, vomiting, diarrhoea and lethargy. |
Most cats do not present with physical symptoms until around 70-75% of renal function is lost and they are at stage III or IV (3).
Dietary Management of CKD
Many vets will recommend a ‘prescription’ kidney diet for cats with CKD, which has altered protein, phosphorous and sodium levels. However, the condition can be successfully managed with a raw diet, albeit with some certain criteria being met. Some of they key nutrients to consider are Protein, Phosphorous, Moisture, and Fats.
Protein
Cats would naturally choose to obtain their calories from protein and fat. The overall diet macronutrient composition selected by domestic cats in a study was the one highest in protein, with moderate fat levels and minimal carbohydrates (6). The natural prey of cats, which would contain 54% protein, 45% fat and only 1% carbohydrate (7). Protein quality is defined by the amino acid composition of the protein source, as well as its digestibility and bioavailability, which is typically higher in animal sources as opposed to plant materials. It is important to feed cats with CKD highly digestible, quality animal protein.
The efficacy of protein restriction divides opinion, especially when it comes to cats. Unlike in dogs with advanced CKD, where urine protein and creatine levels were high, this is an uncommon finding in cats, and restriction of protein has not been shown to slow disease progression (2). Too little protein in a cat’s diet will lead to weight loss and have a detrimental effect on their overall health. Cats are obligate carnivores, adapted to obtain their energy from meat; this does not change if they develop kidney disease. Giving an obligate carnivore a protein restricted diet will undoubtably cause further muscle and organ wastage. Cats are unable to downregulate hepatic enzyme activity associated with protein metabolism, therefore protein restriction makes cats particularly vulnerable to protein malnutrition.
Protein itself does not contribute to kidney damage; it’s the waste products from its digestion which can cause the issue. Hence, protein restriction is initially suggested to reduce nitrogenous waste (8). In late-stage CKD, nitrogenous waste can build up in the blood, at which point restriction may be necessary. In advanced stages of CKD proteinuria may occur, as damage to the glomerulus causes leakage of protein into the urine, and as the number of functioning nephrons decreases, this will worsen. Whilst protein may need to be moderately reduced to control proteinuria, a very low protein diet is not recommended. In fact, research has suggested that cats with CKD may have higher protein requirement than what is provided in a typical ‘prescription’ kidney diet, to prevent muscle wastage (9)
Protein quality will also have an impact, which affects their digestibility, and subsequent waste products (this is important as the kidney is responsible for removing these). The higher the protein quality, the less nitrogenous waste is left behind when digested (eggs and raw meat are the highest quality protein for cats. Thus, a cat with kidney issues can eat a larger quantity of high-quality protein compared to low-quality protein, without as much waste being left behind. Raw animal protein is most suitable, as less nitrogenous waste is produced than when protein is processed and more challenging to digest (10).
Phosphorous
Dietary phosphorus is an essential nutrient, being a component in DNA, RNA, cell membranes and ATP, making it the spark for life (11). Phosphorus content in the body is maintained by intestinal absorption, and excretion via the kidneys. When kidney function is impaired, phosphorous can accumulate in the blood. Thus, in the case of CKD, a lower phosphorus diet is recommended to ease work on the kidneys. Phosphate binders, such as calcium carbonate, may be used to further reduce phosphorous uptake, by binding the phosphorous in the food, allowing more flexibility when feeding (2). We suggest consulting your vet to discuss your cat’s options.
It is also important to note that not all phosphorus is equal. Inorganic phosphorous proves a greater risk than organic phosphorous for absorption issues. Organic phosphorous is typically water soluble, and present in raw animal and plant ingredients in the diet. Whereas inorganic phosphorous is often added during processing, to meet nutritional requirements (12). In fact, dietary phosphorous from natural food ingredients, such as meat and vegetables, does not appear to affect post-prandial plasma phosphorous levels as drastically (13).
Some low phosphorus meats include: Chicken, Rabbit, Duck
Some medium phosphorous meats include: Beef, Turkey
The highest phosphorous foods are considered to be bones, dairy and organ meat (particularly liver), however this does not mean these foods need to be avoided, they should just be fed in moderation. The best way to reduce phosphorous is feeding fattier meats, containing moderate amounts of quality protein.
Moisture
Ensuring adequate hydration is important in all animals but is particularly important for those with kidney disease. Feeding a dry food with inherently low moisture content (<10%), will exert chronic stress on the kidney. Originally, cats evolved to absorb most of their hydration through their food, from eating prey such as mice and birds which consist of around 70% water. This water content is mimicked by a raw diet. Cats have a naturally low thirst drive, meaning that they are slower to respond to dehydration. It is important that cats remain in a constant state of hydration to support kidney health.
The ability to concentrate their urine may contribute to poor urinary tract health commonly seen in cats, an issue which can be exasperated by diet. When dietary moisture content is increased from 10% to 75%, a cat’s urine volume doubles (14). Some studies suggest that cats on an exclusively dry diet do not consume enough water to meet the same hydration status as those on a raw or wet diet (14).
Fats
Inflammation is a primary factor contributing to the development of kidney disease. The excess carbohydrates and cooked fats in dry foods can elevate Omega 6 levels, and subsequently impact the Omega 6:3 ratio, becoming pro-inflammatory (4). Omega 3 fatty acid supplementation is suggested, specifically DHA and EPA due to their anti-inflammatory properties and renoprotective effects (8). In experimental studies, supplementation of DHA and EPA reduced proteinuria in late stage kidney disease (15). Occasional supplementation with salmon oil can provide cats with a good source of additional omega 3.
So, What Criteria Should My Raw Diet Meet?
In the early stages of CKD, a complete, fresh raw meat diet, is the best diet you can offer, but as the disease progresses you may need to tweak the diet, by dropping the phosphorous content, eventually, protein may need to be dropped in end stage CKD.
Palatability is another key aspect of the diet, especially in elderly pets, as circulating toxins and reduced olfactory senses can cause a disinterest in food (2). In fact, inappetence affects up to 92% of cats with the condition (15). Raw food contains fresh fats, making it naturally palatable. Additionally, fresh raw kidney is packed with nutrients that the kidneys need, particularly water-soluble B vitamins. It is important to ensure these are present in the diet, as they’re often lost due to excessive urination. Kidney packs a punch nutritionally, so only feed as 3-5% of the diet, to ensure you do not feed too much phosphorous.
Cat with advanced stage CKD should have high quality protein, potentially in a lower quantity, with low phosphorous levels. A moderately restricted yet high quality protein diet is suggested to reduce the work on the kidney and nitrogenous waste products which can exasperate symptoms (2).
References
- Conroy, M. et al. (2019) ‘Chronic kidney disease in cats attending primary care practice in the UK: a VetCompass study,’ Veterinary Record, 184(17), 526. Available at: https://doi.org/10.1136/vr.105100
- Collins, S. (2016) ‘The role of nutritional management of cats and dogs with renal disease,’ Veterinary Nursing Journal, 31(8), 237-240. Available at: http://dx.doi.org/10.1080/17415349.2016.1194634
- Brown, S. A. (2013) ‘Renal Dysfunction in Small Animals,’ MSD Veterinary Manual. Available at: https://www.msdvetmanual.com/urinary-system/noninfectious-diseases-of-the-urinary-system-in-small-animals/renal-dysfunction-in-small-animals
- Olson, L. (2010) Raw & Natural Nutrition For Dogs
- Brown, S. A. (2018) ‘Noninfectious Diseases of the Urinary System in Dogs,’ MSD Veterinary Manual. https://www.msdvetmanual.com/dog-owners/kidney-and-urinary-tract-disorders-of-dogs/noninfectious-diseases-of-the-urinary-system-in-dogs
- Salaun, F. (2016) ‘Impact of macronutrient composition and palatability in wet diets on food selection in cats,’ Journal of Animal Physiology and Animal Nutrition, 101(2), 320-328. Available at: https://doi.org/10.1111/jpn.12542
- Kirk, C. A. ‘Cats and Carbohydrates – What is the Impact?’ World Small Animal Veterinary Association World Congress Proceedings, 2011. Available at: https://www.vin.com/apputil/content/defaultadv1.aspx?id=5189562&pid=11343&print=1
- Cline, M. G. (2016) ‘Nutritional Management of Chronic Kidney Disease in Cats and Dogs,’ Today’s Veterinary Practice.’ Available at: https://todaysveterinarypractice.com/nutrition/acvn-nutrition-notesnutritional-management-of-chronic-kidney-disease-in-cats-dogs/
- Machado, D. P. (2022) ‘Body Composition of Healthy Cats and Cats with Chronic Kidney Disease Fed on a Dry Diet Low in Phosphorous with Maintenance Protein,’ Toxins, 14(12), 865. Available at: https://doi.org/10.3390/toxins14120865
- Kerr, K. R. et al. (2012) ‘Apparent total tract energy and macronutrient digestibility and fecal fermentative end-product concentrations of domestic cats fed extruded, raw beef-based, and cooked beef-based diets, Journal of Animal Science, 90(2), 515-522. Available at: https://doi.org/10.2527/jas.2010-3266
- Patton, R. (2011) Ruined by excess, perfected by lack: the paradox of pet nutrition.
- Stockman, J. (2024) ‘Dietary Phosphorus and Renal Disease in Cats,’ Journal of Feline Medicine in Surgery, 26, 1-6. Available at: https://doi.org/10.1177/1098612×241283355
- Coltherd, J. C. et al. (2018) ‘Not all forms of dietary phosphorous are equal: an evaluation of postprandial phosphorous concentrations in the plasma of the cat,’ British Journal of Nutrition, 121, 270-284. Available at: https://doi.org/10.1017/s0007114518003379
- National Research Council (2006) Nutrient Requirements of Dogs and Cats
- Parker, V. J. (2021) ‘Nutritional Management for Dogs and Cats with Chronic Kidney Disease,’ Veterinary Clinics of North America: Small Animal Practice, 51, 685-710. Available at: https://doi.org/10.1016/j.cvsm.2021.01.007
Lucy James, BSc (Hons) Bioveterinary Science
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