Failing Filtration: Kidney Disease

Updated: Dec 16, 2021

My family lost their first companion, a cat named Sebsation, in 2009. At fifteen, Sebastion a huge tuxedo cat, already had hyperthyroidism and horrible breath requiring an expensive dental surgery in which he had 9 teeth pulled. When the dental did not clear up his health concerns, through bloodwork it was determined he also was in kidney failure. Sadly, it was only a week after this diagnosis that our beloved cat crossed the Rainbow Bridge. Unfortunately, this fate for many of the world’s companions is very similar.

The purpose of the kidneys is to filter out wastes and by-products which end up in the urine (1, 2) . They also control vitamin D to maintain proper calcium levels and control blood pressure (3). When the kidneys fail these processes cannot occur properly. Sadly, it seems that animals suffer about 75% kidney function loss before they start behaving differently and us humans notice there is a problem (4). At this point there is little we can do for our furry friend in regards of reversing the condition (although no impossible). Simply we can typically ionly attempt to maintain or prevent further progression of the disease.

Although kidney failure can be a result of genetic predisposition(5, 6) and age (7, 8) many would be surprised to know that diet can be a heavy influencer as well. Most of the world’s companions live off of a dry commercial pet food (9), with dry commercial treats and maybe the occasional table scrape or wet food topper. First of all, dry pet food is exactly what it says it is… dry. Commercial dry kibble contains only 7-10% moisture (check any bag of cat or dog food), which for a bodily system like the kidneys that depends and functions on water, this is detrimental (10).


Commercial food also contains artificial ingredients such as vitamins and minerals that are laboratory made from petroleum, tars and coals that are only toxins that the kidney’s hopefully can filter out (11, 12, 13, 14). In addition, the vitamins and minerals are added as premixes to pet foods in large quantities that surpass recommendations (15, 16) in the hopes of accommodating not only a large range of animal companions that will be eating this food, but also for nutrition loss during the cooking and manufacturing processes (17). This means that ingredients that further tax the kidneys are included in pet foods in less than appropriate quantities. Most commercial pet foods are heated at such high temperatures almost all nutrients are destroyed resulting in the manufacturer having to add in artificial vitamins and minerals, they add colors to entice the owners which have their own long list os side effects (18, 19), chemical preservatives like BHA and BHT (20) as well as fruits, vegetables and grains that are not able to be digested properly (21). Although the job of the kidney’s is to filter out toxins and particulates in the body, an over load of these waste products can heavily damage the now over worked kidney’s. This is what is similarly seen in humans that are heavy drinkers and who damage their liver.

When it comes to providing a diet conducive to slowing the progression of kidney failure there are many factors to consider and many that are brought to our attention by the pet food industry and our companions’ veterinarians. One of the first and foremost concerns that many people bring up is protein and the kidneys. Many veterinarians will tell patients to restrict protein informing them that protein causes the kidney’s to work harder and fail faster. Although there is some truth to this in that any kind of processing the kidneys need to do will work them it is also not true. In fact, protein restriction actually is detrimental to the condition and the animal. One study performed on rats that showed rats in kidney failure needed restricted protein in order to slow progression of the disease (22). Because many studies are performed on small laboratory animals, scientists generalized the study to both dogs and cats. However, studies including one that goes back to 1979 with several performed thereafter in 1985 (23), 1986 (24) and the 2000’s (25) have proven dogs and cats REQUIRE protein to slow the progression of kidney failure.

Although protein does increase a few waste products such as urea nitrogen that is concerning in kidney failure (26), studies have shown low/restricted protein versus moderate protein inclusion caused further damage, there is no evidence at this time that high protein negatively affects the kidneys (27). What is important is quality and fresh protein sources. Low quality proteins such as corn, soy and animal by-products only exacerbates the body’s immune system and basic kidney function (28, 29, 30).

Reducing animal based protein in favor of plant based proteins found in commercial pet food instead further stresses the body making most commercial pet food and prescription diets actually counterproductive to preventing the progression to kidney failure (31). Reducing protein also leads to protein starvation and muscle wasting (32). Because cats, dogs and ferrets are carnivores they thrive on protein, with less protein in the diet the body must source it elsewhere and unfortunately that means the body’s own protein reserves. As a result, the body begins to waste away and essentially attack itself further lowering the bodies defense and fight against the actual disease. Another important consideration is the quality of protein. High quality animal proteins should be provided versus low quality plant proteins in order to maintain function (33. Most of the commercial pet foods on the market are made with inferior protein sources which are not digested effectively as they are either plant material (corn (34) and soy (35) or disease/contaminated in some way (animal by-products) taxing the bodies of our canine, feline and ferret friends (36, 37).

What should be restricted in the diet of a companion in kidney failure is phosphorus.The kidney’s now have a decreased ability to excrete phosphorus (38). As mentioned above vitamin D regulation is partially maintained by the kidneys so when these two components are no longer being excreted and regulated properly calcium becomes imbalanced often resulting in demineralization of the bone (39, 40). Furthermore, the build-up of calcium and phosphorus in the kidneys results in inflammation, scarring and lose of proper filtration. Most pet food companies do not list phosphorus content on their bag or canned food labels. Some provide this information on their websites while others may need to be contacted directly for the exact values. The AAFCO recommends a minimum of 0.4% and maximum of 1.6% for a healthy adult dog and 0.5% minimum with no listed maximum for cats. Some suggest dogs in kidney failure should have phosphorus levels between 0.2% and 0.5% while for cat’s simply less than 0.5% is recommended (41).

Moisture is essential as well. Besides the fact that water is essential to life, the kidneys are designed to filter liquids. If the body is not consuming enough liquid for example the common domestic cat who is of desert descent and notorious for retaining water or a second example dry kibble diets which contain only 7-10% moisture, then the kidney’s work dubbly hard simply to do their basic job. After years and years of this strenuous work, there is no surprise the kidneys become taxed and fail gradually over time or in some cases very quickly.

In conjunction with maintaining high levels of moisture, is reducing sodium levels. It is well known that high levels of sodium dehydrates the body but it can also affect blood pressure (42). Although sodium is required for basic physiological function too much is certainly a problem. Although guidelines for sodium requirements are loose as in there is no maximum according to the AAFCO, sodium levels should be a minimum of 0.08% for adult dogs and 0.02% for cats however these numbers are for commercial adult pet foods and there really is no sodium value for animals in kidney failure (41). So we can only assume it should be below the values for healthy adult companions. Although most pet food companies do not list this value on their pet food labels, most are loaded with sodium mainly because companies claim it’s for taste enhancement.

So if commercial and prescription diets only damage the kidney’s further, what do you do? A raw diet of course! Raw diets are the best type of diet in general but in regards to kidney failure raw diets hopefully will prevent nutrition induced kidney failure as well as to prevent further progression of declining kidney function in those already suffering the disease. Raw diets if done properly are made of high quality animal proteins that maintain the integrity of the kidneys and keep them functioning at their best capacity (43). The protein prevents the body from using its own protein reserves preventing bodily wasting and protein starvation. Although some waste products of protein like urea nitrogen are of concern with companions in kidney failure, meat is a natural diet most often free of carbohydrates, dyes, artificial colors, flavors, artificial vitamins and minerals as well as nasty chemical preservatives that are all too common in commercial pet foods INCLUDING prescription veterinary diets. Raw and fresh organs and meat are very high in water content. Water not only is essential for life but it is required to easily filter toxins, waste and unnecessary particles from the body which result in the urine our companions produce. Raw meat also has a natural but low level of sodium content which is ideal for preventing dehydration and further fluid loss. Although a raw diet cannot ensure the reversal of kidney failure, it surely can enable your companion to have a fighting chance of living a longer life with slower progression of the disease and prevention of the disease before it even begins.


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