Physiological Needs of Cats

Calorie Needs and Weight Issues

Protein and the Low Protein Debate







Essential Fatty Acids

Amino Acids, Including Taurine and Astro's Protein Powder



Feeding Frequency

Dry Food versus Canned Food




Site Overview

What You Need to Know First

Alphabetical Index


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What Happens in CKD

Causes of CKD

How Bad is It?

Is There Any Hope?

Acute Kidney Injury



Nausea, Vomiting, Appetite Loss and Excess Stomach Acid

Maintaining Hydration

The Importance of Phosphorus Control

All About Hypertension

All About Anaemia

All About Constipation

Potassium Imbalances

Metabolic Acidosis

Kidney Stones



Coping with CKD

Tanya's Support Group

Success Stories



Alphabetical List of Symptoms and Treatments

Fluid and Urinary  Imbalances (Dehydration, Overhydration and Urinary Issues)

Waste Product Regulation Imbalances (Vomiting, Appetite Loss, Excess Stomach Acid, Gastro-intestinal Problems, Mouth Ulcers Etc.)

Phosphorus and Calcium Imbalances

Miscellaneous Symptoms (Pain, Hiding Etc.)



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Which Tests to Have and Frequency of Testing

Factors that Affect Test Results

Normal Ranges

International and US Measuring Systems



Which Treatments are Essential

Fluid and Urinary Issues (Fluid Retention, Infections, Incontinence, Proteinuria)

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Miscellaneous Treatments: Stem Cell Transplants, ACE Inhibitors - Fortekor, Steroids, Kidney Transplants)

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ESAs (Aranesp, Epogen etc.) for Severe Anaemia

General Health Issues in a CKD Cat: Fleas, Arthritis, Dementia, Vaccinations

Tips on Medicating Your Cat

Obtaining Supplies Cheaply in the UK, USA and Canada

Working with Your Vet and Recordkeeping



Nutritional Requirements of CKD Cats

The B Vitamins (Including Methylcobalamin)

What to Feed (and What to Avoid)

Persuading Your Cat to Eat

Food Data Tables

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Home > Diet and Nutrition > Nutritional Requirements



  • This section contains information on the nutritional requirements of CKD cats, and includes a discussion of the low protein debate.

  • It also discusses other nutritional issues, such as whether to free feed, and the relative merits of dry and canned food.

  • If you're feeling overwhelmed and just want some ideas on what to feed your cat, skip this page for now and read the Which Foods to Feed and Persuading Your Cat To Eat pages instead.

Physiological Needs of Cats                                                                           Back to Page Index


Cats are not small dogs. They have unique physiological needs. When you are dealing with CKD, you need to meet these basic needs but also cater as far as possible for their CKD-related needs.


Basic Physiological Needs

There are many different opinions about the best food for cats, and the debate can get quite heated. I don't wish to focus on that here, but rather to explain the basic needs of cats from a scientific perspective.


Cats are obligate carnivores. This does not mean they can only eat meat. It means that, unlike other species, such as humans and dogs, they cannot themselves manufacture certain amino acids essential to life. In order to obtain these amino acids, they must eat food which contains them, and ideally that means they must eat meat, though they may also be able to obtain them from other sources (corn gluten meal, the protein part of corn, actually contains all the amino acids which cats need).


It is a myth that our domestic cats are miniature versions of the big cats such as lions. Big cats are part of a pride, and hunt together. Domestic cats, in contrast, are solitary predators, and if they are living in their own version of the wild, they only eat what they can catch. They catch mice, insects, whatever passes by or what they can hunt. This means they have evolved to eat little and often. They eat very little plant material or carbohydrate, only what would be found in a mouse's stomach, though they may sometimes also eat small amounts of grass.


Originally cats were desert animals, so they evolved not to want to drink much. Since a mouse is approximately 60% water, historically this was not an issue - they got sufficient fluid intake from their food. Therefore ideally cats also need to eat foods containing a reasonable amount of water.


Geometric analysis of macronutrient selection in the adult domestic cat, Felis catus (2011) Hewson-Hughes AK, Hewson-Hughes VL, Miller AT, Hall SR, Simpson SJ & Raubenheimer D Journal of Experimental Biology 214 pp1039-1051 found that "the intake target lies close to 26g day protein, 9g day fat and 8g day carbohydrate, yielding a macronutrient energy composition of 52% protein, 36% fat and 12% carbohydrate."


So to summarise, healthy cats need foods containing a large percentage of meat-based protein, with limited vegetables and grains. They need to eat little and often, and ideally a wet food containing around 60% moisture; but the ingredients are more important.


The feeding behavior of the cat (2010) Horwitz D, Soulard Y & Junien-Castagna A Encyclopaedia of Feline Nutrition pp439-477 is an excellent overview of feline eating habits.


Physiological Needs of CKD Cats

It becomes a little more complicated when you add CKD to the mix. You still want to feed a diet that meets your cat's basic physiological needs, as outlined above, but if possible you also want to feed a diet that can help with the CKD.


There are two main concerns with diet in CKD cats. Firstly, ideally you do not want to feed anything that may make the disease progress faster and/or make the cat feel poorly. Secondly, you want to keep your cat eating and keep weight and muscle on.


Below I discuss the components of diet, such as protein and phosphorus, and also how some of the other issues relating to feline needs (such as free feeding) tie in with CKD. The protein section includes information about the pros and cons of a low protein diet.


I recommend that you read this page so you can understand the main components of feline diets, and why prescription renal diets differ from normal diets. Then you can read about Which Foods to feed, which discusses the introduction of prescription diets and what to do if your cat refuses to eat them. Remember, the most important thing is that your cat eats. I cannot emphasise this enough. If you're struggling to get any food at all into your cat, check the Persuading Your Cat to Eat page.


Calorie Needs and Weight Issues                                                                  Back to Page Index


Weight and Body Condition

You should monitor your cat's weight and body condition closely. Weight loss is one of the major headaches of CKD. It happens partly because many CKD cats have poor appetites, and partly because older cats have a natural tendency to lose weight, particularly in the form of muscle mass. However, CKD cats also lose weight because of the disease. Mechanisms causing loss of lean body mass in kidney disease (1999) Mitch WE The American Journal of Clinical Nutrition 67 pp359-66 explains more about this problem in humans. Anorexic cats (who have stopped eating) and cachexic cats (cats who have lost a lot of muscle) have a worse prognosis than cats of a normal weight, so it is essential to monitor weight and calorie intake, and above all to keep your cat eating.


Purina has a Body Condition diagram showing how to gauge your cat's physical condition. In Staged management of chronic kidney disease in dogs and cats (2009) Presentation to the World Small Animal Veterinary Association World Congress, Dr D Polzin says: "Ideally patients should consume sufficient calories from an appropriate diet to maintain a body condition score of 4 to 5/9. Increased efforts are indicated to assure sufficient calorie intake for patients with body condition scores of 3/9 or lower or when patients fail to consume adequate calories to maintain a stable, appropriate body weight."


If you are lucky enough to have an overweight CKD cat, rejoice, and certainly don't put him or her on a diet, because as the CKD progresses, your cat will almost certainly lose weight anyway.


Calorie Needs

Feeding a teaspoonful of food a day is not going to be enough to maintain your cat's weight, let alone increase it if your cat is too thin. A healthy cat needs approximately 30-35 calories per day per pound of body weight, or possibly more if the cat is particularly active. As an example, a 9 lb (4.1kg) cat would need 270-315 calories a day. The National Research Council states that a lean adult cat weighing 5 lbs needs around 170 calories a day, and a lean adult cat weighing 10 pounds needs around 280 calories a day.


This level of intake may not be sufficient for older cats. In Feeding older cats - an update in new nutritional therapies (2011) Sparkes A Topics in Companion Animal Medicine 26(1) pp37-42, Dr Sparkes states that older cats need more calories than younger cats, preferably in the form of protein. He adds that older cats also seem to do better when fed a diet containing prebiotics, antioxidants and essential fatty acids. Many sources, including the National Research Council, also believe that chronically sick cats need more calories, possibly as many as twice the number of calories as healthy cats.


When considering a food, you not only need to consider phosphorus and protein levels (see the Food Data Tables for information on phosphorus and protein levels in a variety of commercial foods), but you also need to consider the calorie content. Most canned foods contain around 80% water, but some are as much as 85% water. Whilst increased fluid content can be helpful for CKD cats, who are at risk of dehydration, the downside is that such foods may make the cat feel relatively full while providing insufficient calories for the cat's needs (see below). This is often the case with simple foods that consist largely of meat or fish. Lower fat foods may also contain fewer calories.


Some manufacturers provide data about the metabolisable energy (ME) of their foods. Metabolizable energy: a way to looks at caloric density by Dr Holly Nash explains how foods vary in terms of the number of calories which are actually available to a cat after digestion: "Pet foods with higher ME numbers provide your pet's body with more concentrated calories for more energy. With a higher ME, your pet's body will receive more energy from a smaller amount of food." This can be helpful for CKD cats who tend not to have much appetite.


I am often asked if I could add calorie details to the food data tables. I do plan to do this, but in the meantime you can check the food you are considering feeding for the ME levels, or find the calorie content of some US foods here (canned) and here (dry).


Stanley Marks discusses feline dietary and calorie needs in Diagnostic and therapeutic approach to the anorectic cat (2001), Presentation to the World Small Animal Veterinary Association World Congress 2001.

Petdiets can help you work out how much food your cat needs each day.


Food Composition and Requirements                                                          Back to Page Index


The usual guidelines for CKD cats are to feed a diet which has added potassium but which is low in protein, phosphorus and sodium. It is helpful to understand the reasoning behind these recommendations. 


Protein                                                                                                                 Back to Page Index

What is Protein?

Protein is a molecular structure made up of a number of amino acids which are essential for the body to repair and maintain itself.


Cats have a higher need for protein than many other species because, unlike dogs or humans, they cannot manufacture certain of these amino acids (e.g. taurine) within their bodies but instead have to obtain them from their food. These missing amino acids are only found in meat (and corn gluten meal), and therefore cats must ideally eat meat in order to obtain these amino acids. This is why cats are known as obligate carnivores. When people feed a cat a vegetarian diet (which I definitely do not recommend for any cat), they provide these amino acids in the form of supplements, but cats are optimally designed to obtain them from meat.


Feline Protein Requirements

Nutrient Requirements of Cats states that healthy cats need an absolute minimum of 3.97g of protein per kg of cat, or 1.8g per lb of cat, so a 4.5kg or 10lb cat would need a minimum of 18g of protein a day. Geometric analysis of macronutrient selection in the adult domestic cat, Felis catus (2011) Hewson-Hughes AK, Hewson-Hughes VL, Miller AT, Hall SR, Simpson SJ & Raubenheimer D Journal of Experimental Biology 214 pp1039-1051 found that in fact for the average cat, "the intake target lies close to 26g day protein..., yielding a macronutrient energy composition of 52% protein." Dr D Zoran believes that healthy cats should eat a diet containing around 45% protein on a dry matter analysis (DMA) basis.


This level of intake may not be sufficient for older cats. In Feeding old cats - an update in new nutritional therapies (2011) Sparkes A Topics in Companion Animal Medicine 26(1) pp37-42, Dr Sparkes states that older cats need more calories than younger cats, preferably in the form of protein. He adds that older cats also seem to do better when fed a diet containing prebioticsantioxidants and essential fatty acids.


As far as CKD cats are concerned, in Slowing the progression of chronic renal failure (2004), Dr DF Grauer states that the minimum protein requirements of cats with CKD are higher than those of healthy cats. However, he recommends that cats should receive "a minimum of 3.3 to 3.5 g of protein per kilogram body weight per day", which is actually less than recommended for healthy cats in Nutrient Requirements of Cats above. He also states "At the same time, the patient’s serum creatinine and albumin concentrations as well as their body weight should be stable."


Ohio State University states that protein should never be reduced to less than 20% of calories for CKD cats (scroll down to the slides labelled Conservative Medical Management of CRF: Protein Restriction?).


What is High Quality Protein?

During the breakdown of dietary protein in the digestive process, waste substances are created which are filtered out of the blood by the kidneys and excreted via urination. This is sometimes referred to as the removal of nitrogenous wastes. Unfortunately damaged kidneys find it harder to do this, which is why BUN levels rise in CKD.


Thus the goal in CKD is to feed a protein with the correct balance of amino acids to provide the cat with the ability to maintain and repair bodily tissues, but in a form which needs as little breaking down as possible. That is what we mean in this context by "high quality protein." In other words, if you feed a human grade cat food that contains expensive organic chicken breast, you may not necessarily be providing high quality protein in the form that is required for a CKD cat.


Pet Education has an overview of protein requirements in cats.


Why Vets Recommend Low Protein

The reasoning behind this recommendation is that feeding a low protein diet reduces the amount of nitrogenous wastes that must be processed by the kidneys.  This usually leads to a reduction in BUN levels and in turn the cat will often feel and act better. Nutritional management of feline chronic kidney disease (2008) Elliott J, Elliott D Veterinary Focus 18(2) pp39-44 states that this is "most appropriate for late Stage 3 and Stage 4 CKD cats."


This paper also states that protein restriction may "decrease proteinuria mediated by glomerular hyperfiltration, a mal-adaptive response to CKD which contributes to progressive renal injury. This is the reason for reducing protein intake in Stages 2 and 3 of CKD." However, the authors themselves admit that "The efficacy of reducing protein intake as a treatment for proteinuria is highly controversial in the cat and dog."


It must be remembered that when vets recommend prescription renal diets, they are not only recommending low protein. Prescription kidney diets have other attributes, for example lower protein diets also tend to contain less phosphorus, and phosphorus control is extremely important in CKD cats (see below). You can read more about the attributes of prescription kidney diets on the Which Foods to Feed page.


The Low Protein Debate

There is a lot of controversy about how useful low protein diets are for CKD cats, and when they should be introduced. Part of the controversy arises from the fact that many of the older studies which advocate the feeding of lower protein diets to CKD patients were performed on humans and rats, and therefore their findings may not be appropriate for cats, with their uniquely complex nutritional needs.


There are some studies into the use of low protein diets in CKD cats. In Effects of dietary protein and calorie restriction in clinically normal cats and in cats with surgically induced chronic renal failure (1993) Adams LG Polzin DJ Osborne CA & O'Brien TD American Journal of Veterinary Research 54 pp1653-1662, CKD cats were fed either high (38%) or low (20%) protein diets for one year. The cats fed a high protein diet had higher BUN levels (as might be expected) than the cats fed a low protein diet (who were fed 2.7g/kg per day) but they also had lower creatinine levels; and they also ate more and gained weight compared to the cats on the low protein diet, some of whom showed signs of malnutrition towards the end of the study. Some of the cats fed the high protein diet did develop transient hypokalaemia (low potassium levels), which might have been because the low protein diet contained more potassium. Please note that the CKD cats in this study did not have naturally occurring kidney disease.


In Protein and calorie effects on progression of induced chronic renal failure in cats (1998) Finco DR, Brown SA, Brown CA, Crowell WA, Sunvold G & Cooper TL American Journal of Veterinary Research 59 pp575-582, cats were divided into four groups: low protein, low calorie (A); low protein, high calorie (B); high protein, low calorie (C); and high calorie, high protein (D). No real differences were seen after a year, and there was no change in GFR in any group. A vet from Ohio State University College of Veterinary Medicine stated with regard to this study: "recent findings in cats with induced renal insufficiency suggest that feeding diets restricted in protein may not be necessary for this species. Cats fed 9g of protein per kg of bodyweight per day had no more severe kidney lesions or lower GFR than did cats fed 5.2g  of protein per kg of bodyweight per day". In Effects of dietary protein intake on renal function (1999) Supplement to Compendium on Continuing Education for the Practising Veterinarian 21 Dr Finco stated "the negative results from the second study indicate that protein restriction in cats with renal disease remains to be proven as an effective maneuver for ameliorating progression of renal disease". 


There are also some studies into the use of prescription kidney diets, which of course are not only low protein. In Survival of cats with naturally occurring chronic renal failure: effect of dietary management (2000) Elliott J, Rawlings JM, Markwell PJ, Barber PJ Journal of Small Animal Practice 41 pp235-42, 29 cats were fed a low protein, low phosphorus prescription diet, while a further 21 cats did not eat the prescription diet. Some of the cats (presumably in both groups) were also given phosphorus binders. The cats fed the prescription diet survived longer than the other cats, but it is not clear whether this was due to the reduction in phosphorus intake rather than the reduction in protein intake. The study concluded "Feeding a veterinary clinical diet (with intestinal phosphate binders where necessary) specifically formulated for feline renal failure was associated with a highly significant beneficial effect on survival of cats presenting with naturally occurring stable CKD. This is the first prospective dietary study involving naturally occurring feline CKD cases where survival from first diagnosis has been assessed."


Nutritional management of feline chronic kidney disease (2008) Elliott J, Elliott D Veterinary Focus 18(2) pp39-44 states that "protein restriction may "decrease proteinuria mediated by glomerular hyperfiltration, a mal-adaptive response to CKD which contributes to progressive renal injury. This is the reason for reducing protein intake in Stages 2 and 3 of CKD." However, the authors themselves admit that "The efficacy of reducing protein intake as a treatment for proteinuria is highly controversial in the cat and dog", adding that this may lead to malnutrition.


The study that most experts cite when recommending a prescription kidney diet is Clinical evaluation of dietary modification for treatment of spontaneous chronic kidney disease in cats (2006) Ross SJ, Osborne CA, Kirk CA, Lowry SR, Koehler LA, Polzin DJ Journal of the American Veterinary Medical Association 229(6) pp949-57. This study found that feeding a prescription kidney diet helped to keep BUN levels lower and appeared to help prevent metabolic acidosis in cats with more advanced CKD. The study concluded "The renal diet evaluated in this study [Hill's k/d] was superior to an adult maintenance diet in minimizing uremic episodes and renal-related deaths in cats with spontaneous stage 2 or 3 CKD." By Stages 2 and 3, they are referring to cats with creatinine between 2.1 and 4.5 mg/dl.


The Downsides of Low Protein

One problem with lowering protein intake in cats is that it may have unintended side effects. In Slowing the progression of chronic renal failure (2004) Dr GF Grauer states that "There are, however, potential undesirable effects associated with dietary protein reduction. Specifically, if dietary protein is restricted in relation to the animal’s protein needs, reduced renal hemodynamics, protein depletion (decreased body weight, muscle mass, and serum albumin concentration), anemia, and acidosis can occur or be aggravated."


Low protein diets are also of concern for cats with metabolic acidosis, because, according to Nutrition and renal function in cats and dogs: acid-base, electrolytes and renal failure (1999) Polzin DJ, Osbourne CA, James K Supplement to Compendium on Continuing Education for the Practising Veterinarian 21 11(K), studies of rats and humans with renal failure show that "acidosis may limit the ability of patients to adapt to dietary protein restrictions." It is not yet certain whether acidosis also affects cats in this way, but it seems plausible, given the cat's relatively high requirement for protein.


Should I Feed Low Protein?


IRIS Stages 1 and 2

Because of the potential downsides of protein restriction, it is not necessarily a good idea to feed low protein food in all cases. For cats in Stage 1 or early Stage 2 of CKD under the IRIS system (creatinine between 1.6 and 2.8 mg/dl, or 140 and 250 mmol/L), the risks of low protein food may outweigh the benefits, and therefore many vets do not advocate protein restriction in these stages. In Managing chronic diseases in cats (2005) Veterinary Medicine Dr S Little states "Don't restrict dietary protein for cats experiencing mild to moderate chronic renal insufficiency (creatinine 1.6 to 2.8 mg/dl, 140 to 250 μmol/l) because it can lead to protein malnutrition. These cats require adequate protein and calories to maintain body weight and to avoid muscle wasting and anemia."


If your cat also has hyperthyroidism, it can be even more of a concern since hyperthyroid cats are prone to weight loss and muscle wasting. In Diet and nutritional management for hyperthyroid cats (2011) Dr ME Peterson states that for cats with both CKD and hyperthyroidism, reducing protein should be avoided for cats in IRIS stages 1 and 2, but that phosphorus control is very important.


If you decide not to feed low protein, please do ensure that your cat has a low phosphorus intake.


IRIS Stages 3 and 4

Since BUN is influenced by protein intake, it does often help the cat feel better if you restrict protein intake as the CKD progresses. Generally speaking, once BUN levels are over 60, you are more likely to see symptoms such as vomiting and nausea, so this is a point at which many vets recommend that you start restricting protein intake. In Slowing the progression of chronic renal failure (2004) Dr GF Grauer states that "As the renal failure progresses, additional dietary protein reduction will likely be necessary. Dietary protein reduction should be initiated when the animal’s blood urea nitrogen concentration is between 60 and 80 mg/dl."


The usual goal is around 25% protein on a dry matter analysis (DMA) basis. For most people, the easiest way to achieve this is to feed a renal prescription diet: these diets have a protein level of around 25-30%. You can also check the Food Data Tables to find other foods which are relatively low in protein, but don't forget the prescription diets do not only consist of low protein, and the protein they do contain is good quality from the CKD perspective.


Unfortunately, it can often be easier to switch a cat to a low protein diet when the cat is stable with lower numbers. So if your early stage cat is prepared to eat a low protein renal diet, it is worth feeding. The manufacturers claim that their diets have adequate protein levels for cats at every stage of CKD, but if you are concerned, consider adding foods with high biologic value but minimal nitrogenous waste. A good choice would be eggs.


If your cat has been diagnosed with CKD and has BUN over 60 (urea over 21), you may panic if you cannot get your cat to eat a low protein food. Take a deep breath. In Managing chronic diseases in cats (2005) Veterinary Medicine Dr S Little states "Never try to force an anorexic patient with chronic renal insufficiency to eat a protein-restricted diet. Instead, concentrate on encouraging anorexic patients to eat." Focus on getting food into your cat and getting him or her stabilised before you worry about feeding low protein. See the Which Foods to Feed page for more tips on getting your cat to eat the prescription diet and what to do if you can't succeed. See the Persuading Your Cat To Eat page for tips on getting your cat to eat. See below for information on Astro's Protein Powder. Whatever you do, monitor your cat's weight closely.


Phosphorus                                                                                                        Back to Page Index


In contrast to the protein debate, there is no dispute about the importance of controlling phosphorus levels for CKD cats. High phosphorus levels are very damaging to their health and can make the disease progress more quickly.


This is such an important topic that I have an entire page devoted to phosphorus control. Please read it and do everything you can to keep your cat's phosphorus levels low - it can make all the difference to your cat's health and prolong survival.


Fat                                                                                                                         Back to Page Index


Just as cats need a diet relatively high in protein, so they also need relatively high levels of fat compared to a human or dog. Geometric analysis of macronutrient selection in the adult domestic cat, Felis catus (2011) Hewson-Hughes AK, Hewson-Hughes VL, Miller AT, Hall SR, Simpson SJ & Raubenheimer D Journal of Experimental Biology 214 pp1039-1051 found that the fat target for healthy cats is about 9g a day or 36%.


Fat does not result in a lot of waste products like protein, so processing it is not a strain on the kidneys; plus cholesterol is not an issue for cats the way it is for humans (see blood chemistry panel). Fat has been implicated in the development of obesity in healthy cats, but obesity is hardly a problem for the average CKD cat. Thus, a diet relatively high in fat can help a CKD cat to maintain his/her weight whilst placing less strain on the kidneys.  


In most CKD prescription foods, the fat content is increased to compensate for the lower protein levels; but many senior cat foods also have relatively high levels of fat and relatively low levels of protein; as a bonus, they often also have low phosphorus. Therefore, if your cat won't eat prescription foods, it is worth considering senior foods.


Sodium                                                                                                                 Back to Page Index


The kidneys cannot process sodium as effectively in CKD, which increases the risk of hypertension (high blood pressure) in humans. It used to be thought that the same applied to cats, and it was therefore recommended that sodium intake should be restricted. However, one study, Effects of dietary sodium chloride intake on renal function and blood pressure in cats with normal and reduced renal function (2004) Buranakarl C, Mathur S & Brown SA American Journal of Veterinary Research 65(5) pp620-7 found that "this common dietary maneuver could contribute to hypokalemic nephropathy and progressive renal injury in cats."


A later study, Effects of sodium chloride on selected parameters in cats (2006) Kirk CA, Jewell DE, Lowry SR Veterinary Therapeutics: Research in Applied Veterinary Medicine 7(4) pp333-346 found that sodium intake appeared to have no effect on in blood pressure in CKD cats, but that levels of BUN, creatinine and phosphorus were higher in the cats eating a high sodium diet compared to those eating a low sodium diet.


Effects of dietary sodium chloride on health parameters in mature cats (2009) Xu H, Laflamme DP & Long GL Journal of Feline Medicine & Surgery 11(6) pp435-41 examined a low sodium diet (0.55%) and a high sodium diet (1.11%) fed to mature cats over a period of six months. Even in cats with creatinine over 1.6mg/dl, "there remained no evidence of adverse effects associated with increased salt intake. These results are consistent with the majority of other studies evaluating sodium intake in cats, as well as with the National Research Council's assessment, all of which indicate that sodium at 1.5% of the diet dm is not harmful to healthy cats."


Pet food safety: sodium in pet foods (2008) Chandler ML Topics in Companion Animal Medicine 23(3) pp148-53 states that "there is no strong evidence that increased dietary sodium increases the risk of hypertension in dogs and cats, and the current recommendation for hypertensive animals is to avoid high dietary salt intake without making a specific effort to restrict it... Increased dietary sodium increases urine output and may decrease the risk of forming calcium oxalate uroliths due to the decrease in relative supersaturation of solutes. However, caution should be used in increasing the sodium intake of patients with renal disease as increased dietary sodium may have a negative effect on the kidneys independent of any effect on blood pressure."


So should you restrict sodium intake or not? The International Renal Interest Society states on page 5 that there is no evidence that reducing sodium intake is helpful for CKD cats, and that it should certainly not take the place of medication for hypertension, but if you do opt to do this, you should do it gradually. The food data tables provide information about the sodium content of many cat foods available in the USA and UK.


Potassium                                                                                                           Back to Page Index


Around 30% of CKD cats have potassium levels which are too low. This occurs because potassium is easily lost through increased urination and vomiting. The prescription foods contain extra potassium (all cat foods need some potassium), and this is usually in the form of potassium citrate, because potassium citrate may help with a problem seen in some CKD cats known as metabolic acidosis.


If your cat refuses to eat a prescription diet, your vet can give you a potassium supplement instead, if appropriate; some cats need a potassium supplement whether or not they eat the prescription food. 


Many commercial cat foods are acidified in order to reduce the risk of FLUTD (feline lower urinary tract disease. These foods often say that they are designed to maintain urinary tract health; or they may contain cranberries or additional Vitamin C. However, these foods (which are actually designed to treat a different kind of problem to CKD) may have the effect of increasing the amounts of potassium lost in the urine, which is bad for CKD cats. It is therefore best not to feed acidified foods to CKD cats, who tend to have quite high acid levels anyway. 



Carbohydrates                                                                                                   Back to Page Index


Cats only have a limited need for carbohydrates - a cat catching his/her own food would only eat the small amount of carbohydrate contained in a mouse's stomach. Geometric analysis of macronutrient selection in the adult domestic cat, Felis catus (2011) Hewson-Hughes AK, Hewson-Hughes VL, Miller AT, Hall SR, Simpson SJ & Raubenheimer D Journal of Experimental Biology 214 pp1039-1051 found that target intake for carbohydrate in cats was only 8g a day or 12% of total food intake. It also states "Our analysis indicates that cats have a ceiling for carbohydrate intake, which limits ingestion and constrains them to deficits in protein and fat intake (relative to their target) on high-carbohydrate foods."


In The carnivore connection to nutrition in cats (2002) Zoran D Journal of the American Veterinary Medical Association 221 pp1559-67, Dr Zoran writes "It is clear that cats have a greater need than dogs or other omnivores for protein in their diet. Cats also have several physiologic adaptations that reflect their expected low CHO [carbohydrate] intake... These specific differences do not mean cats cannot use starch. In fact, cats are extremely efficient in their use of simple sugars. However, it does underscore their development as carnivores and the expected low amounts of grain in their typical diet. These digestive differences may mean that high amounts of CHO in diets may have untoward effects on cats."


Therefore, if you are trying to reduce your CKD cat's protein intake, I would recommend increasing the fat in the diet (see below) rather than the carbohydrates. If you are feeding a prescription diet, this will often be done automatically - many of these diets increase the fat content (rather than the carbohydrates) in order to offset the reduced protein content.


Pet Education has an interesting article about carbohydrates in the feline diet.


Fibre                                                                                                                      Back to Page Index


Fibre is the non-digestible component of complex carbohydrate. It is important for good digestive health. It may also assist with two commonly seen CKD problems, toxin reduction (via nitrogen trapping) and the control of constipation.


There are two different types, fermentable and non-fermentable. Which fibres are fermentable depends upon the species. Fermentability of selected fibrous substrates by cats (1994) Sunvold GD, Titgemeyer EC, Bourquin LD, Fahey GC & Reinhart GA The Journal of Nutrition 124 pp2721S-2722S examines the degree of fermentability of various fibres. Diet and large intestinal disease in dogs and cats (1998) JW Simpson The Journal of Nutrition 128 2717S-2722S has a table showing soluble and fermentable fibres.


In terms of general health, you do not necessarily want the most fermentable fibres. Dietary fiber for cats: in vitro fermentation of selected fiber sources by cat fecal inoculum and in vivo utilization of diets containing selected fiber sources and their blends (1995) Sunvold GD, Fahey GC Jr, Merchen NR, Bourquin LD, Titgemeyer EC, Bauer LL & Reinhart GA Journal of Animal Science 73(8) pp2329-39 examined the fermentability of various fibres. It concludes that the diet "which contained the most fermentable fibers, severely decreased nutrient digestibility and resulted in poor stool characteristics. Diets that contain moderately fermentable fiber provide fermentation end products that may be important in maintaining the health of the gastrointestinal tract of the cat."


Nitrogen Trapping

There has long been interest in whether other bodily mechanisms might be useful for relieving the load on damaged CKD kidneys. Bowel as a substitute in renal failure (1996) EA Friedman American Journal of Kidney Diseases 28(6) pp943-50 states "Extraction, modification, or recycling of nitrogenous wastes by the gastrointestinal tract is a potentially low-cost means of substituting for missing renal function. Multiple approaches to the bowel as a substitute kidney have been attempted."


One way of doing this may be via increased fibre intake, specifically fermentable fibre. Fermentable fibre provides a source of carbohydrate for the bacteria in the gut. These bacteria, which are essential to health, increase in number when provided with additional fermentable fibre, and the more bacteria there are, the more nitrogen is excreted in the faeces. This increased faecal excretion, which is sometimes referred to as "nitrogen trapping", may help to reduce the load on the kidneys by diverting the excretion of urea from the kidneys.


A 1999 study Role of fermentable carbohydrate supplements with a low-protein diet in the course of chronic renal failure: experimental bases Younes H, Alphonse JC, Behr SR, Demigné C, & Rémésy C American Journal of Kidney Disease 33(4) pp633-46 indicated that the use of fermentable fibre may help reduce BUN levels. Fermentable carbohydrate supplementation alters nitrogen excretion in chronic renal failure (2006) Younes H, Egret N, Hadj-Abdelkader M, Remesy C, Demigne C, Gueret C, Deteix P, Alphonse JC Journal of Renal Nutrition 16(1) pp67-74, a more recent study into the use of fibre to reduce BUN levels, suggests that this method appears to have similar benefits to protein restriction without the drawbacks of protein restriction.


Prescription kidney diets contain fermentable fibre, because some is always needed to feed the gut bacteria. Iams has patented a Nitrogen Trap Fiber System containing beet fibre for use in their kidney prescription food. Hill's uses both beet fibre and locust bean gum.


Unfortunately, Nutritional management of feline chronic kidney disease (2008) Elliott J, Elliott D Veterinary Focus 18(2) pp39-44 states "classic uremic toxins, unlike urea nitrogen, are medium sized molecules, too large to easily pass through the membrane barrier. It is therefore unlikely that these toxins may be used by the bacteria to cater for their nitrogen needs. Conversely, the beneficial effects of fermentable fibers can help to regulate the digestive disorders that accompany CKD."


Some forms of fibre, such as fructooligosaccharides (FOS), may also bind calcium in the small intestine and lead to an increase in calcium levels in the body (hypercalcaemia). This is not  good for cats with high calcium levels. Inulin and guar gum may do this, as may slippery elm bark and lactulose, two treatments commonly used for constipation in CKD cats. The effects of gum arabic oral treatment on the metabolic profile of chronic renal failure patients under regular haemodialysis in Central Sudan (2008) Ali AA, Ali KE, Fadlalla AE & Khalid KE Natural Product Research 22(1) p12-21 found that patients given gum arabic for three months had lower BUN, creatinine and phosphorus levels, but calcium levels increased significantly.


Too much fibre may also prevent your cat from absorbing sufficient nutrients or calories from his/her food. Fibre may also affect taurine levels in some foods. I would therefore recommend discussing additional fibre with your vet before adding it, and avoiding its use in a cat who already has high calcium levels.


You can read more about waste product regulation in the Treatments section.



Non-fermentable fibre can be helpful for CKD cats because it reduces the risk of constipation, a common problem in CKD cats, by holding water in the stool. Most commercial cat foods have sufficient levels of fibre for a healthy cat, but if your cat suffers from constipation you may wish to add more fibre in the form of something such as pumpkin, baby peas or psyllium. Please see Constipation for more information on dealing with constipation. 


Feline Constipation explains more about fibre and gut health.


Essential Fatty Acids (EFAs)                                                                           Back to Page Index

What are Essential Fatty Acids

Essential fatty acids are polyunsaturated fats (sometimes abbreviated as PUFA). They are essential because the body cannot synthesise them, so they have to be obtained from food. The two main types of EFAs are Omega-3 and Omega-6. Commercial diets tend to contain far more Omega-6, partly because Omega-6 EFAs are cheaper and more stable, but this may create a potentially harmful imbalance. The correct balance is not yet known, though some believe it is probably around 5:1 (Omega-6:Omega-3). Qualitative risk assessment of chronic renal failure development in healthy, female cats as based on the content of eicosapentaenoic acid in adipose tissue and that of arachidonic acid in plasma cholesteryl esters (2005) Plantinga EA, Hovenier R & Beynen AC Veterinary Research Communications 29(4) pp281-6 concluded that "the fatty acid composition of cat foods should be determined and that, if deemed necessary, the ingredient composition should be altered so that the content of EPA [eicosapentaenoic acid, an Omega-3 type] is raised and that of AA [arachidonic acid, an Omega-6 type] is lowered."


Essential fatty acids appear to be helpful with many bodily functions. It has been known for many years that they have an effect on the skin - the first signs of an imbalance or deficiency are usually a dry coat, itchy skin or matted fur. Recently it appears that they may have an important role in controlling inflammation. In one study, Effect of nutritional interventions on longevity in senior cats (2007) Cupp CJ, Jean-Philippe C, Kerr WW, Patil AR & Perez-Camargo G The International Journal of Applied Research in Veterinary Medicine 5(3), healthy older cats fed a diet containing antioxidants including additional essential fatty acids lived significantly longer.


Dietary omega-3 fatty acid supplementation increases the rate of muscle protein synthesis in older adults: a randomized controlled trial (2011) Smith GI, Atherton P, Reeds DN, Mohammed BS, Rankin D, Rennie MJ, Mittendorfer B American Journal of Clinical Nutrition 93(2) pp402-12 investigated the effects of EFAs on loss of muscle mass in healthy older human adults (sarcopaenia). It concluded "Omega-3 fatty acids stimulate muscle protein synthesis in older adults and may be useful for the prevention and treatment of sarcopenia."


Essential Fatty Acids for CKD Cats

Whether to supplement essential fatty acids in CKD cats is a grey area. Research in rats and humans appears to indicate that the addition of omega-3 fatty acids to the diet may delay the progression of CKD. However, in Nutritional management of renal disease (2008) Presentation to the World Small Animal Veterinary Association World Congress, Dr K Sturgess states that "it is possible that supplementation of diets with PUFA may increase renal damage associated with lipid peroxidation (degradation of carbon=carbon double bond by oxidants). The benefits over risks of increasing PUFA levels in the diets of cats with CRD have not been established." It goes on to say that the ratio of Omega 3 to Omega 6 may be crucial.


Nutrition and renal function: effects of dietary lipids on renal function (1999) Polzin  DJ, Osbourne CA, James K, Purina Research Report, adapted from articles presented at the 1998 Purina Nutrition Forum sees things differently. It states: "In cats, dietary supplementation with n-3 PUFA had no apparent deleterious effect on lipid metabolism, immune function, blood pressure, or renal function. At higher levels of supplementation, renal function was actually increased in normal cats. These data support the assertion that this dietary maneuver is safe for normal cats and provides some encouragement for further consideration for dietary n-3 PUFA supplementation in cats with renal disease, systemic hypertension, or hypersensitivity reactions."

Retrospective study of the survival of cats with acquired chronic renal insufficiency offered different commercial diets (2005) Plantinga EA, Everts H, Kastelein AM & Beynen AC Veterinary Record 157(7) pp185-187 found that cats who ate prescription kidney diets with the highest amount of EPA survived for 23 months versus an average of 12 months for cats who ate diets containing lower EPA levels.

Oxidative stress and chronic kidney disease (2008) Brown SA The Veterinary Clinics of North America. Small Animal Practice 38(1) pp157-66 concludes that "newer data indicate that dietary supplementation with specific antioxidants is an important consideration for limiting renal oxidant stress and progression of CKD." He mentions PUFA as an antioxidant earlier in the text.


Prescription renal diets have increased levels of essential fatty acids compared to normal cat food. Almost everybody I know of who has added essential fatty acids to their cat's treatment plan has been happy with the results, reporting an improvement in general wellbeing. Ask your vet if it is appropriate for your cat.


Types of Supplement

Since cats as obligate carnivores benefit from animal-based products, the most appropriate form of essential fatty acid supplement is fish oil. Fish oil contains Omega-3 fatty acids in the form of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). However, oils from the liver, such as cod liver oil, are not suitable because they contain too much Vitamin A and D. Feeding the aging heart (2010) Freeman LM & Rush JE Nestlé Purina Companion Animal Nutrition Summit 2010 Focus on Gerontology states (page 62) "cod liver oil should not be used to provide omega-3 fatty acids because it contains high levels of vitamins A and D, which can result in toxicity." Look for an oil pressed from the flesh only and containing EPA and DHA.


Vegetable-based oils, such as olive oil or flax seed (linseed) oil, are also not recommended, because they do not contain the essential fatty acids which a cat needs. The University of Connecticut discusses EFAs added to food and mentions that alpha linolenic acid should be ignored because it is of limited use to cats. Dietary fish oil and flaxseed oil suppress inflammation and immunity in cats (2011) Park HJ, Park JS, Hayek MG, Reinhart GA, Chew BP Veterinary Immunology & Immunopathology 141(3-4) pp301-6 found that "fish and flaxseed oil can reduce skin inflammatory responses in cats, however, flaxseed oil appears less immunosuppressive than fish oil." Feeding the aging heart (2010) Freeman LM & Rush JE Nestlé Purina Companion Animal Nutrition Summit 2010 Focus on Gerontology states "Flaxseed or flaxseed oil also should not be used because its omega-3 fatty acids cannot be efficiently converted to EPA and DHA in dogs (and particularly in cats)."


If fish oils are given, extra Vitamin E is also required in order to avoid a problem called steatitis. Vitamin E requirement of adult cats increases slightly with high dietary intake of polyunsaturated fatty acids (2002) Hendriks WH, Wu YB, Shields RG, Newcomb M, Rutherfurd KJ, Belay T & Wilson J The Journal of Nutrition: Supplement: Waltham International Symposium 132 pp1613S-1615S discusses this. Too much vitamin E can be dangerous, so ask your vet how much to give. Veterinary products often contain Vitamin E in an appropriate dosage (it may be referred to as tocopherol).


Astro's CRF Oil was created by a human doctor to treat his own CKD cat, and has been on the market since January 2007. The manufacturer states that the product was tested on an informal basis on 18 CKD cats in the Montreal area over a period of about eight months. This product is basically a combination of essential fatty acids, Vitamin E and CoQ10 (ubiquinon), both antioxidants, but in a concentrated formula. You can read more about it in the Treatments section.



It can be a bit tricky working out an appropriate dose of fish oil. There is no definitive dose, and many of the recommendations relate to a particular amount of EPA (eicosapentaenoic acid), so you will need to check the product you're considering to see how much EPA it contains. Many fish oil capsules are 1000mg strength. However, only around 20% of it tends to be EPA (with around 10% DHA), so a 1000mg capsule will contain around 200mg of EPA and 100mg of DHA.


One recommended dose of EPA is 22mg per kg of cat per day, or 10mg per lb of cat per day. So if your cat weighs 8 lb (3.6kg), you would give a product containing 80mg of EPA each day.


Another recommended dosage is 180 EPA and 120 DHA per 10 lbs (4.5kg) of cat. As you can see, this is more than double the earlier dose.


Generally speaking, it is probably safe to give your cat one 1000mg fish oil capsule daily. Do check with your vet first though. Renal prescription diets contain increased amounts of EFAs, so if your cat is eating such a food, you may not need additional supplementation, or may need a reduced dose.


Essential fatty acids are commonly available in either capsule form or in pump bottles. Do not give the oil directly into your cat's mouth, or s/he may aspirate the oil. Instead, mix the oil (you can open the capsule) with your cat's food. You don't have to give the daily dose in one amount, you can divide it between your cat's meals.


Although most cats like fish, the oils can be a bit strong, and many cats dislike the smell. Some cats may vomit after eating them. It is therefore wise to start off very slowly, just using one drop at first which you add to a smelly food that may disguise the test, and gradually increase the dose over several days or even weeks, If your cat still hates it, you can decant the oil into a gelcap, try finding a less smelly product, or discuss with your vet whether to continue with the supplement. Some members of my support group find krill oil is more acceptable to their cats.


It takes 2-3 months to see the full effect of essential fatty acid supplements. If you think they help your cat, you should use them on an ongoing basis.


Essential fatty acids can turn rancid quite easily. Keep them in the fridge, and check them regularly to see if they smell off before using them.



Veterinary products are helpful for working out cat-sized dosages but often contain Omega 6 and/or Omega 9 fatty acids, which you don't need, so ensure your selected product only contains Omega 3 oils. Many people simply use human products, and in some cases they and their cat use the same one.



Pet Education has a very helpful overview of essential fatty acids, with a comparison of various brands available in the USA.

Consumer Lab has a summary of its findings with regard to the quality of EFAs, including the names of some of the US products which met with its approval.

Environmental Defense Fund has a table showing which brands remove contaminants from their products.

Welactin is a veterinary product available in both softgel capsules and pump bottle. One capsule contains 150mg EPA and 100mg DHA. One pump contains approximately 1.8 ml and provides 140mg of EPA and 216mg of DHA.

CVS sells Sundown Naturals Fish Oil 1000mg with total EPA and DHA of 300mg.

Grizzly Salmon Oil is made from wild Alaskan salmon.

Twinlab makes a krill oil product called Krill Essentials which some people find their cats tolerate better. This is also available from other suppliers, such as Vitacost, among others. The dosage for krill oil (which is made from crustaceans rather than fish) is 500mg per day.

Amazon sells Now Neptune krill oil for US$30.14 for 120 capsules.



Salmopet is a salmon-based fish oil which is widely available in Europe. I haven't managed to work out its precise composition, but Vet UK mentions that it has an EPA/DHA content of 15-25%, and it also contains Omega 6 oils (which is not ideal). Your vet may also have a suitable product in stock.


Amino Acids, Particularly Taurine                                                                 Back to Page Index


Amino acids are the components of protein. There are 23 amino acids which cats need, and they can manufacture twelve of these themselves, but the other eleven must be obtained from food. Taurine is one example of an amino acid which cats must obtain from food. Virginia-Maryland Regional College of Veterinary Medicine explains more about cats and amino acids.


Plasma amino acid profiles in cats with naturally acquired chronic renal failure (1999) Goldstein RE, Marks SL, Cowgill LD, Kass PH & Rogers QR American Journal of Veterinary Research 60(1) pp109-13, found that CKD cats in all stages of the disease had lower levels of amino acids than healthy cats. However, they concluded "the magnitude of these changes is mild and of little clinical relevance." This is an older study, and it might eventually be shown that supplementary amino acids are in fact helpful to CKD cats.


Inflammation contributes to low plasma amino avid concentrations in patients with chronic kidney disease (2005) Suliman ME, Rashid Qureshi A, Stenvinkel P, Pecoits-Filho R, Bárány P, Heimbürger O, Anderstam B, Rodriguez Ayala E, Divino Filho JC, Alvestrand A & Lindholm B American Journal of Clinical Nutrition 82(2) pp342-349 also found that amino acid levels are low in human CKD patients with inflammation and states that the inflammation may be the cause. Oral supplement of six selective amino acids arrests progression of renal failure in uremic patients (2004) Yatzidis H International Urology and Nephrology 36(4) pp91-8 found that amino acid supplements appeared to help human patients with glomerulonephritis.


If you feed a commercial diet, it will contain the correct balance of amino acids for cats. However, if you feed homemade food, it is critical to ensure that the diet has the correct balance of amino acids. Some highlights in elucidating the peculiar nutritional needs of cats (2007) Morris JG & Rogers QR Nestle Purina 2007 Nutrition Forum Proceedings found that problems related to amino acid deficiencies occurred after a couple of weeks, but that problems relating to a lack of arginine occurred within less than a day (arginine deficiency can be fatal in cats very quickly).



The amino acid of greatest relevance to cats is taurine. Taurine is most concentrated in the heart, retinas (eyes) and the brain. In the cat, it is essential for the digestion of fats, which cannot be achieved without taurine in the diet. Since taurine is only found in animal-based products, this is one reason why cats are obligate carnivores - eating the flesh of another animal is the easiest and best way for a cat to take in an adequate amount of taurine. However, Plasma amino acid and whole blood taurine concentrations in cats eating commercially prepared diets (2009) Heinze CR, Larsen JA, Kass PH & Fascetti AJ American Journal of Veterinary Research 70 p1374 found that there was little correlation between the amount of protein in the diet and taurine levels in the cat's blood.


A lack of sufficient taurine in a cat's diet can cause blindness and a type of heart disease called dilated cardiomyopathy. Dietary rice bran decreases plasma and whole-blood taurine in cats (2002) Stratton-Phelps M, Backus RC, Rogers QR & Fascetti AJ Journal of Nutrition 132 pp1745S-47S mentions that studies have shown that "Cats fed canned foods require a higher quantity of taurine than those fed dry foods to prevent taurine deficiency resulting from alterations in the bioavailability of taurine attributed to the effects of processing." Feline nutrition update (2001) Biourge V Presentation to the World Small Animal Veterinary Association World Congress states "studies at Davis found that dry extruded cat foods required about 1 g/kg diet, but canned foods required up to 2.5 g/kg


 If cats eat a higher fat or higher fibre canned diet, they may also require additional taurine. Dietary rice bran decreases plasma and whole-blood taurine in cats (2002) Stratton-Phelps M, Backus RC, Rogers QR & Fascetti AJ Journal of Nutrition 132 pp1745S-47S mentions that "In addition to processing, both the fiber and fat content of canned feline diets may affect taurine metabolism through an alteration of intestinal bacteria and subsequent changes in the excretion of bile acids."


Taurine and inflammation: a new approach to an old problem (1997) Letter in the Journal of Leukocyte Biology 61(2) pp231-2 concludes "we believe that taurine may play a vital role in the management of inflammation."


There is plenty of taurine in all cat foods, and an even higher level in prescription kidney diets. However, some people do choose to give taurine supplements to their CKD cats. Taurine is water soluble, so any excess should be urinated out. However, Accumulation of taurine in patients with renal failure (2002) Suliman ME, Bárány P, Divino Filho JC, Lindholm B & Bergström J Nephrology Dialysis Transplantation 17(3) found that some human renal patients given taurine supplements complained of feeling dizzy, and tests showed that their taurine levels were far in excess of normal following supplementation. Unlike cats, the human body can produce its own taurine, so this might be a factor in the side effects seen in this study. I don't know if there would be a similar risk with cats, but please do not supplement taurine without your vet's approval.


Vitacost sells 3 oz of Source Naturals taurine powder for US$5.59.



One of the other amino acids that cats require is arginine. Arginine: an essential amino acid for cats (1978) Morris JC & Rogers QR The Journal of Nutrition 108 pp1944-53 explains more about arginine. Arginine is important for insulin production in cats, and is also necessary to convert ammonia into urea, a role so important that a cat fed a diet deficient in arginine will develop high ammonia levels and may die. Some highlights in elucidating the peculiar nutritional needs of cats (2007) Morris JG & Rogers QR Nestle Purina 2007 Nutrition Forum Proceedings explains that severe problems relating to a lack of arginine occurred within less than a day, with one cat dying.


Arginine is also used to make nitrous oxide in the kidneys. It is thought that nitrous oxide plays a critical role in regulating blood flow through the kidneys, and it is known that the amount of blood flowing through the kidneys can affect kidney function. L-arginine levels are often very low in CKD cats. Nitric acid deficiency in chronic kidney disease (2008) Baylis C American Journal of Physiology & Renal Physiology 294(1) ppF1-9 explains more about this and states that restoring nitrous oxide production may slow the progression of kidney disease. Role of L-arginine in the pathogenesis and treatment of renal disease (2004) Cherla G and Jaimes EA Journal of Nutrition 134 pp2801S-6S found that l-arginine supplementation may be helpful or harmful in CKD. It appears to be detrimental in cases of glomerulonephritis. See the Research page for more information on feline research into this issue.


I would not supplement l-arginine without your vet's approval.



This is an amino acid which encourages the natural production of BMP-7, which may help the kidneys regenerate. Apparently studies are in hand for human CKD patients with this amino acid but I don't know anybody who has used it in a cat. Do not use it without checking with your vet first.


Astro's Protein Powder

The maker of Astro's CRF Oil also offers Astro's CRF Protein Powder, though it is not advertised on the website. It was apparently tested on 24 cats and 11 dogs. The supplement is 96% amino acids made from wild, deep sea white fish which is enzymatically pre-digested (fish protein hydrolysate) so the amino acids are very low molecular weight and therefore need no processing by the digestive tract. In other words, the product apparently creates very little nitrogenous waste. It is intended to counteract some of the side effects of low protein diets in CKD patients (muscle and weight loss and malnutrition). It can be used in conjunction with Astro's CRF Oil, or added to prescription kidney diets to supplement protein and calorie intake without placing extra strain upon the kidneys.


The powder is odourless and water soluble. Ideally it should be given about twenty minutes before food - it can be mixed with water and syringed in or offered as is in a bowl (apparently some cats like the taste and will eat it like this). The recommended dose is a quarter of a tsp per 10lb (4.5kg) of cat 1-2 times a day. It costs US$32.95 plus shipping costs for a 100g jar which would last 2-3 months for most cats.


I am not aware of any studies into the use of fish protein hydrolysate in CKD patients but it appears to be helpful with other conditions. Reparative properties of a commercial fish protein hydrolysate preparation (2005) Fitzgerald AJ, Rai PS,  Marchbank T, Taylor GW, Ghosh S, Ritz BW, Playford RJ Gut 54 pp775-781 found that fish protein hydrolysate significantly reduced gastric injury in rats and concluded "Fish protein hydrolysate possesses biological activity when analysed in a variety of models of injury and repair and could provide a novel inexpensive approach for the prevention and treatment of the injurious effects of non-steroidal anti-inflammatory drugs and other ulcerative conditions of the bowel." Another study, Fish protein hydrolysate reduces plasma total cholesterol, increases the proportion of HDL cholesterol, and lowers Acyl-CoA:cholesterol in liver of Zucker rats (2004) Wergedahl H, Liaset B, Gudbrandsen OA, Lied E, Espe M, Muna Z, Mørk S and Berge RK Journal of Nutrition 134 pp1320-7, concluded that fish protein hydrolysate "may have a role as a cardioprotective nutrient."


I have heard from a few people who have used this product and are happy with it. They say it has increased their cats' appetites. The best way for cats to take in the correct balance of amino acids is normally from eating a complete food designed for cats, but if you do want to try this product, run it by your vet first. It can be obtained by going to Astro's CRF Oil and emailing the manufacturer, who will then send you a Paypal invoice.


Vitamins                                                                                                               Back to Page Index


If your cat is eating prescription food, in principle additional vitamins should not be necessary, since suitable extra vitamins are added to these foods. However, if your cat is not eating these foods, additional vitamins may be necessary.


Vitamin B is helpful for most CKD cats regardless of whether they are eating or not, and is particularly important for cats who are anaemic.


Do not give vitamins to your cat without your vet's approval because excess vitamin intake can be very dangerous.

The National Academy of Science gives guidelines on the daily vitamin requirements of cats.


Vitamins A and D

These vitamins are fat soluble, and are stored in the body rather then excreted. For this reason, there is a risk of toxicity when supplementing these vitamins. Vitamins A and D also promote calcification, which is a risk with CKD cats who have a tendency towards calcification anyway.


In any event, deficiencies in these vitamins are extremely rare, so it is highly unlikely that your cat requires supplementation of any kind; plus care should be taken when considering the use of multi-vitamin tablets, which may contain these vitamins. 


Feeding the aging heart (2010) Freeman LM & Rush JE Nestlé Purina Companion Animal Nutrition Summit 2010 Focus on Gerontology states "cod liver oil should not be used to provide omega-3 fatty acids because it contains high levels of vitamins A and D, which can result in toxicity."

Dr Katherine James mentions (Section K, Dietary Management) that Vitamins A and D may cause toxicity in CKD cats.


DVM News Magazine states on page 2 that fat soluble vitamins should not be given to excess.


Vitamin B                                                                                                               

Although Vitamin B is commonly referred to as if it were a single vitamin, there are actually a number of B vitamins. These are essential vitamins, which means that they cannot be manufactured in the cat's body, so must be obtained from external sources (from food or a supplement).


B vitamins are water-soluble, so are often lacking in CKD cats, who lose much of their Vitamin B through urination. Cats who are not eating much will also probably not be taking in enough B vitamins.


B vitamins are so important for CKD cats that there is a separate page about them.


Vitamin C

Additional vitamin C is not usually a good idea for CKD cats, because it is acidifying and CKD cats already have a tendency towards acidosis. Medline Plus mentions that Vitamin C may also interact adversely with products containing aluminium, such as phosphorus binders.


Vitamin C-induced hyperoxaluria causing reversible tubulointerstitial nephritis and chronic renal failure: a case report (2007) Rathi S, Kern W & Lau K Journal of Medical Case Reports 1 p155 reports on a case where a man developed CKD after taking large doses of Vitamin C, which proved to be reversible following proactive treatment and stopping the Vitamin C.


In any event, unlike humans, cats are able to produce their own Vitamin C, so it is usually unnecessary to add it to their diet. However, one study did find that using Vitamin C as an antioxidant in conjunction with other vitamins did appear to be effective. See Treatments for more information on this study.


Vitamin E

Vitamin E is an antioxidant, and studies are taking place into the role of antioxidants in improving health. The Winn Feline Foundation gave a grant to Colorado State University in 2010 for a study into "Vitamin E as a Novel Treatment for the Anemia of Feline Chronic Renal Failure." This study was completed in 2013 and the results should be published in 2014.


Addressing age-related changes in feline digestion (2010) Patil AR & Cupp CJ Nestlé Purina Companion Animal Nutrition Summit 2010 Focus on Gerontology states "if Vitamins E & B12 are at low levels, then processing of fat and protein are likely compromised in older cats."


If you are giving fish oil-based essential fatty acids, Vitamin E is also often given in order to avoid steatitis. See essential fatty acids for more information.


Water                                                                                                                     Back to Page Index


Water is critical for CKD cats. In order to maintain hydration, a cat generally needs around 24-30ml of water per pound bodyweight per day (though this amount will be affected by activity levels and climate). This means that a 10lb (4.5kg) cat would require 240-300ml of water a day (a cat in congestive heart failure may need less).


The cat does not need to obtain this by drinking alone. If you are feeding canned food, which contains a lot of water, that will make a sizeable contribution to total intake. Effects of feeding frequency on water intake in cats (2005) Kirschvink N, Lhoest E., Leemans J. Delvaux F, Istasse L, Gustin P, Diez M Journal of Veterinary Internal Medicine 19 p476 found that cats fed more frequently increased their fluid intake.


Cats in the wild do not eat and drink in the same place. Therefore it is better not to put the water bowl next to the food bowl. Some cats don't like a narrow bowl where their whiskers touch the side, so experiment, and also consider using a water fountain (see below).


Some people find placing ice cubes made from low sodium tuna water in their cat's water bowl encourages their cat to drink more. You may also wish to give your cat homemade chicken broth to drink.


With a CKD cat, it makes a lot of sense to have more than one water source. We used to just have one bowl of water out but once Thomas was diagnosed we switched to three, including one placed upstairs so Thomas didn't have to go too far for a drink in the night. 


Some people give their cat bottled or distilled water. The taste of chlorine in normal tap water doesn't taste too good to cats, so this is worth considering but not essential. Some types of distilled water have a low pH level, and the extra acidity in these products is not appropriate for CKD cats, who tend towards acidity anyway. We give our cats filtered water, at room temperature, and change it several times a day (changing the water so frequently is not necessary with water fountains, see below)..


Cats on subcutaneous fluids may drink less, because some of their hydration needs are being met through the fluid administration. This is not normally something to worry about, though ensure you don't see other symptoms that might, taken together, indicate crashing.


Daily water requirements and needs for cats (2011) Peterson ME discusses feline water needs.

Hill's Pet Tails Monthly Newsletter (2011) explains why cats may prefer running water and gives tips on increasing your cat's water intake.

Pet Education has some tips on how to get your cat to drink more.

About Cats Online has tips on how to get your cat to drink.


Water Fountains

Many people find water fountains increase their cat's water intake. Effect of water source on intake and urine concentration in healthy cats (2010) Grant DC Journal of Feline Medicine and Surgery 12(6) pp431-4 found that cats drank a bit more from a water fountain but there was not a massive difference. This was a short study though. I found my cats needed time to get used to the fountain, but that they did drink more from it once they were used to it.


There are three main types of water fountain:

My cats have used the large (deluxe) version of the Fresh Flow for several years and they love it (see photo above). Some people find the Catit easier to clean. Any of them should be fine for most cats.


When you first get a fountain, leave it out without water in for a few days to allow your cats to get used to it. Then add water, but don't turn it on. Once your cats are drinking from it, turn it on. Be sure to leave other water sources available until you know your cats are willing to use the fountain.


Instructables tells you how to build your own water fountain.

Sixerdoodle Electronics has instructions on adapting your tap (faucet) with a "cat sensor" so your cat can turn it on and off himself.

How cats lap: water uptake by Felis catus (2010) Reis PM, Jung S, Aristoff JM & Stocker R Science 330(6008) pp1231-4 explains how cats use their tongue to lap up water.


Drinking Fountain Sources



Pampered Pet Mart sells the Drinkwell for US$34.95.

Valley Vet sells the Petmate Freshflow Water Fountain in the USA for US$33.95 or US$37.95 for the larger model.

Miles Kimball sells a small water fountain for US$19.99.

Drs Foster & Smith sell a variety of water fountains with prices starting around US$20.

Amazon sell the Pioneer stainless steel model for US$54.30.

Drs Foster & Smith sell the Drinkwell stainless steel model for US$99.95.

Glacier Point sells a variety of ceramic fountains.

Bottle Babies sells freestanding water bottle holders, similar to the water supplies designed for hamsters etc.



Pet Planet sells the Deluxe Freshflow Fountain for £51.49.

Pet Planet also sells the Cat-It water fountain for £22.99.

Amazon UK sells a variety of water fountains.



Real Canadian Superstore sells the Petmate Freshflow Water Fountain in Western Canada for CAN$29.98.

Dino Direct sells freestanding water bottle holders, similar to the water supplies designed for hamsters etc. Some cats like this sort of fountain.


Other Dietary Issues                                                                                         Back to Page Index


Free Feeding

The National Academy of Science has performed in-depth research into canine and feline nutrition. It states that "If given free access to food, cats will eat between 12 and 20 meals a day, evenly spread out over the 24-hour light-dark cycle. It goes against the nature of the cat to force it to eat only one meal a day."


Effects of feeding frequency on water intake in cats (2005) Kirschvink N, Lhoest E., Leemans J. Delvaux F, Istasse L, Gustin P, Diez M Journal of Veterinary Internal Medicine 19 p476 found that cats fed more frequently increased their fluid intake. Free feeding a CKD cat has an additional benefit, namely that feeding little and often may reduce the problem of excess stomach acid, a common problem in CKD cats.


Dry food tends to lend itself quite well to free feeding, but canned food may be a better choice for CKD cats. If you are out a lot and wish to free feed canned food, an automatic timed feeder is a good idea.



Drs Foster and Smith in the USA sell a variety of feeders.

Mighty Pets sells an eight day automatic feeder for US$71.99.

Petco sells the PetSafe five meal feeder for US$52.99.

Amazon sells the Catmate for US$38.62.

Amazon sells the Petsafe five meal feeder for US$44.85.

Fancy Paws sells a two bowl 48 hour timed feeder for US$35.



Pet Planet sells an automatic feeder in the UK for £29.99.

Zooplus sells a timed feeder for £24.90.


Dry Food versus Canned Food

As desert animals, healthy cats do not drink a lot, but instead they obtain moisture from their prey. A mouse, for example, is around 60% water. Canned cat foods contain even more moisture than this, between 75-85% in most cases, so a healthy cat who eats primarily canned food will not drink much at all.


Issues with Dry Food

Most dry cat foods only contain 8-10% moisture, so cats who eat dry food do tend to drink more than cats fed on wet food, but they simply cannot take in as much moisture overall as a cat fed on tinned food. In Nutrient Requirements of Cats (1986) the US Board of Agriculture stated "cats given dry food do not voluntarily consume water to equal the ratio of water to dry matter of cats given canned diets containing about 75% moisture." The carnivore connection to nutrition in cats (2002) Zoran D Journal of the American Veterinary Medical Association 221 pp1559-67, states "cats eating commercial dry foods will consume approximately half the amount of water (in their diet and through drinking), compared with cats eating canned foods... In older cats that tend to produce urine with a lower concentration, an increase in water consumption becomes even more important to avoid dehydration and development of prerenal azotaemia".


This does not mean that dry foods cause CKD. In fact, 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 (2012) Kerr KR, Vester Boler BM, Morris CL, Liu KJ, Swanson KS Journal of Animal Science 90(2) pp515-22 found that there was no difference in urine concentration between cats fed the three types of diet used in the study (dry food, raw food and home-cooked food). In fact, the cats fed the raw and homemade diets had higher creatinine levels than the cats fed the dry food, though still within range (these were healthy cats).


However, whilst many healthy cats seem to manage fine with dry foods, it may be preferable to give a CKD cat a canned food if possible so as to reduce the possibility of dehydration. The cat food manufacturers produce their CKD diets in both a dry and a canned version, but if you can, try to feed your cat the canned version if at all possible.


Issues with Canned Food

Unfortunately, a recent study, Epidemiologic study of relationships between consumption of commercial canned food and risk of hyperthyroidism in cats (2004) Edinboro CH, Scott-Moncrieff JC, Janovitz E, Thacker HL & Glickman LT Journal of the American Veterinary Medical Association 224 (6) pp 879-886, indicates that cats who eat canned food, particularly from pull-ring cans, appear to be at increased risk of developing hyperthyroidism. It is thought that this may be related to the lining used in these tins, bisphenol-A (BPA), a potential endocrine disrupter. It is therefore probably worth trying to feed your cat food from foil pouches or plastic trays rather than from tins. If you do use tins, be sure to store any leftover food in glass containers in the fridge rather than in the tins themselves. The Food Standards Agency has more information on this.


Effect of water content in a canned food in voluntary food intake and body weight in cats (2011) Wei A, Fascetti AJ, Villaverde C, Wong RK & Ramsey JJ American Journal of Veterinary Research 72(7) pp918-23 found that healthy cats fed a canned diet ate more than cats fed the same diet in freeze-dried form, but took in less energy and "had a significant decrease in body weight." This is perhaps because the amount of water in canned foods makes the cat feel full more quickly.


Another possible issue with canned food is that some cats find it harder to eat than dry food. Canned food does not allow cats to get their teeth into it as with a mouse. They often have to lap canned food up, almost as if it is liquid. Many cats do this with foods canned in gravy - my Persians (one of whom is not particularly flat-faced) always seem to simply lick the gravy and leave the chunks. Again, this may lead to a lower calorie intake overall. and in severe cases, the cat may go hungry. For this reason I usually feed pate-style canned food, and as my cats eat and spread the food all over the bowl, I put it back into little piles at intervals.


For a CKD cat, a possible compromise, especially with dry food junkies, is to feed them both dry and canned prescription kidney diets. The dry kidney diets tend to be more acceptable to many cats than the canned versions, so if you have a dry food addict, try a dry kidney diet. Some people compromise by feeding a dry renal diet while they are out at work all day, but they then feed a low phosphorus (but non-prescription) diet when they are home.


Dry foods and risk of disease in cats (2008) Buffington CAB Canadian Veterinary Journal 49 p561-3 states that there is little evidence that dry food contributes to diabetes or ill health generally in cats.


AAFP-AAHA Feline Life Stage Guidelines state (page 10) "Both canned and dry food have been found to support health during all life stages. The panel examined published peer-reviewed evidence-based studies in healthy, client-owned cats for any significant health effect of: feeding canned versus dry food (including contribution to dental health); providing a variety of foods versus a consistent diet; feeding high protein, low carbohydrate versus lower calorie and high fiber diets; feeding raw diets; providing dietary supplements, or access to grass or plants.  Based on the available data, specific recommendations in favor of any of these practices cannot be made."


With CKD cats, obviously you wish to avoid dehydration as much as possible, but the most important thing is to keep them eating. If your cat is a dry food junkie, and is prepared to eat dry prescription food, I would consider feeding it. You can always add water to the dry food to make it less dry, though if you do this, you should not leave the food down for too long because it will spoil. An alternative would be to switch to semi-moist renal food in pouches.



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This page last updated: 15 September 2013


Links on this page last checked: 06 April 2012