Search This Site

Early Detection

Share This Site: A Notice for Your Vet's Bulletin Board or Your Local Pet Shop

Overview

• This page starts with a brief overview of the physiological needs of cats generally.

• It then examines the nutritional requirements of CKD cats in particular, and includes a discussion of the reduced protein debate.

• It also discusses other nutritional issues, such as the importance of weight and muscle maintenance.

• 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

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:

1. It is essential to keep your cat eating, and to maintain weight and muscle as much as possible.

2. Ideally you do not want to feed anything that may make the disease progress faster and/or make the cat feel poorly.

Below I discuss the importance of weight management and calorie intake in CKD cats, followed by an explanation of the main components of the feline diet, such as protein and phosphorus, and how they impact on CKD. The protein section includes information about the pros and cons of a reduced protein diet.

I recommend that ideally you read this page so you can understand the main components of feline diets. Then you can read the Which Foods to Feed page, which discusses food choices including therapeutic kidney 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 out the Persuading Your Cat To Eat page.

Weight and Muscle

Maintaining weight and muscle is extremely important. Anorexic cats (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 your cat's weight and body condition closely, and above all to keep your cat eating.

Staged management of chronic kidney disease in dogs and cats (2009) Polzin D Presentation to the World Small Animal Veterinary Association World Congress 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."

The World Small Animal Veterinary Association has a body condition score chart showing how to gauge your cat's physical condition,.

Purina has a guide to hoe to use a body condition score.

If you are lucky enough to have a slightly overweight CKD cat, rejoice, and personally I would not put him or her on a diet, because as the CKD progresses, your cat will almost certainly lose weight anyway.

Weight

Older cats (over the age of ten) are prone to weight loss, even if they have no underlying health problems. It is not known exactly why older cats lose weight, but it is thought it may be at least in part because their bodies become less able to digest nutrients, particularly fat and protein.

Skinny old cats: why some senior cats lose weight. What's going on? (2014) Williams D DVM360 Magazine states "The incidence of low fat digestibility increases with age, affecting 10% to 15% of mature cats (8 to 12 years old) and 30% of geriatric cats (> 12 years old). In some geriatric cats, fat digestibility was found to be as low as 30%, and the only clinical signs were large stools (not frank diarrhea) and low body weight. Low protein digestibility also seems to affect mature and geriatric cats. Although the incidence of low protein digestibility is lower than that of fat digestibility, about 20% of cats older than 14 years show protein digestibility lower than 77%. The incidence of low fat and protein digestibility tends to occur in the same cats. A marked decline apparently becomes particularly prevalent after around age 10."

Whatever the precise reason, weight loss in older cats is not good news. Determining protein requirements —nitrogen balance versus lean body mass (2013) Laflamme DP Nestlé Purina Companion Animal Nutrition Summit Tackling Myths About Pet Nutrition pp42-45 states "Previous research suggests that unexplained weight loss, especially in geriatric cats, can be the first sign of an impending terminal condition." 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) says "there is evidence that extreme leanness in old cats may actually be detrimental. Emaciated cats had a significantly higher risk of death compared with cats in optimal body condition. Perez-Camargo et al demonstrated that body weight, lean body mass, and fat mass decline in cats over the age of 12 years, particularly in the last 1 to 2 years of life."

Even in younger cats, low body weight can be a concern. Strong associations of 9-point body condition scoring with survival and lifespan in cats (2018) Teng KT, McGreevy PD, Toribio JL, Raubenheimer D, Kendall K & Dhand NK Journal of Feline Medicine and Surgery 20 epub looked at over 2600 cats and found that cats with a body condition score of 4 or 5 between the ages of 1 and 3, and a maximum body condition score of 3 between the ages of 3 and 11 had a shorter lifespan than cats with a body condition score of 6. The study concludes "There are significant associations of 9-point body condition scoring with survival and lifespan, and BCSs <5 and of 9 were found to be negatively associated with both."

As far as CKD goes, Risk factors associated with the development of chronic kidney disease in cats evaluated at primary care veterinary hospitals (2014) Greene JP, Lefebvre SL, Wang M, Yang M, Lund EM & Polzin DJ Journal of the American Veterinary Medical Association 244(3) pp320-327 found that median weight loss in CKD cats in the 6-12 months before diagnosis was 10.8%, which was a lot higher than in cats who did not develop CKD. Evaluation of weight loss over time in cats with chronic kidney disease (2016) Freeman LM, Lachaud M-P, Matthews S, Rhodes L & Zollers B Journal of Veterinary Internal Medicine 30(5) pp1661–1666 found that "weight loss was already present 3 years before diagnosis and accelerated after diagnosis of CKD. Cats <4.2 kg at the time of diagnosis had significantly shorter survival time compared to cats ≥ 4.2 kg at diagnosis."

Weight loss in CKD happens partly because many CKD cats have poor appetites, but 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.

Prolonging life and kidney function (2009) Chew DJ & DiBartola SP CVC in Kansas City Proceedings states "Maintenance of stable body weight and serum albumin concentration suggests adequate intake of calories and protein whereas progressive declines in body weight and serum albumin concentration suggest malnutrition or progression of disease and are indications to increase the amount of protein fed."

It is therefore extremely important to monitor your cat's weight and to keep him or her eating. I recommend weighing your cat at least weekly. There are links on buying scales suitable for weighing cats here.

Feline weight loss (2011) Scherck M NAVC Clinician's Brief Nov 2011 pp18-19 has a diagnostic tree to help narrow down the cause of weight loss in a cat.

Muscle

Muscle wasting, or cachexia, is also common in CKD cats. This is partly because most CKD cats are elderly and the elderly are prone to sarcopaenia, which is the age-related loss of muscle.

CKD cats may also suffer from cachexia for other reasons. Cachexia versus sarcopenia  (2011) Rolland Y, Abellan van Kan G, Gillette-Guyonnet S & Vellas B Current Opinion in Clinical Nutrition and Metabolic Care 14(1) pp15-21 states "Sarcopenia is now recognized as a multifactorial geriatric syndrome. Cachexia is defined as a metabolic syndrome in which inflammation is the key feature and so cachexia can be an underlying condition of sarcopenia. Recently, cachexia has been defined as 'a complex metabolic syndrome associated with underlying illness and characterized by loss of muscle mass with or without loss of fat mass. The prominent clinical feature of cachexia is weight loss in adults."

CKD is one such underlying illness. Review of muscle wasting associated with chronic kidney disease (2010) Workeneh BT & Mitch WE American Journal of Clinical Nutrition 91(4) pp1128S-1132S states that muscle wasting is common in human CKD patients, particularly those with inflammation or metabolic acidosis.

Cachexia and sarcopenia: emerging syndromes of importance in dogs and cats (2012) Freeman LM Journal of Veterinary Internal Medicine 26 pp3-17 says "The syndrome of cachexia also appears to be common in companion animals with chronic diseases, such as CHF, CKD, and cancer." Cachexia must be taken seriously. Dr Freeman goes on to say "The prevalence of cachexia in people with CKD is estimated to be 20%. Although the prevalence of cachexia in dogs and cats with CKD has not specifically been measured, it appears to be relatively high and likely has negative clinical effects."

Since creatinine, one of the measures of kidney function, is a by-product of muscle, cats who lose a lot of muscle may have reduced creatinine levels, because they cannot produce as much creatinine. The Merck Veterinary Manual states "Serum creatinine levels can be falsely lowered in patients with severe muscle wasting." Feeding cats with different nutritional needs: a dilemma in the multicat household (2012) Scherk M Presentation to the 73rd SCIVAC International Congress 2012 pp421-430 states "As an obligate carnivore, if a cat doesn’t get enough dietary protein to meet metabolic requirements, he must draw on endogenous (stored) protein sources to meet those needs. Over months cats can down regulate their protein needs and switch to use other pathways, but in the short and intermediate term, muscle will be catabolized. The resulting muscle wasting and decreased mass reduces the serum level of creatinine (Cr) measured."

You may therefore think your cat's CKD is improving because the creatinine is falling, when in fact this is not the case.

Cats with hyperthyroidism also tend to lose a lot of muscle, which is an additional headache if your cat has both CKD and hyperthyroidism.

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 essential fatty acids (see below) 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."

The World Small Animal Veterinary Association has a muscle condition score chart.

Calories

When considering a food for their CKD cats, many people focus on its phosphorus and protein levels, but it is also important to consider the calorie content, especially if you want your cat to maintain or gain weight and muscle.

A healthy cat needs approximately 30-35 calories per day per pound of body weight, or possibly more if the cat is particularly active. Your cat's nutritional needs (2006) 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. The World Small Animal Veterinary Association Nutritional Assessment Guidelines make similar recommendations for the average healthy adult cat at a healthy weight.

This level of intake is unlikely to 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.

Feline CKD therapeutic goals: do not throw away your shot (2018) Wooten SJ DVM360 Magazine reports "The most important thing to ponder about nutrition in feline CKD is whether the cat is eating enough, Dr. St. Denis says. This is more important than what the cat is eating. Maintaining adequate caloric intake and muscle mass is critical to avoid protein malnutrition. But, as you already know, ensuring adequate intake in a cat can be very challenging. Working with the client and providing education in this area is an important therapeutic strategy. If the cat isn't eating enough or is underweight, then Dr. St. Denis recommends feeding 1.2 to 1.4 times the resting energy requirement (RER). Most geriatric cats need at least 1.1 times RER."

So obviously, feeding a teaspoonful of food a day is not going to be enough to maintain your CKD cat's weight, let alone increase it if your cat is too thin. Another thing to consider is the water content of the food. Whilst most canned foods contain around 80% water, some are as high as 85% water. Although 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. This is often the case with simple foods that consist largely of meat or fish. Lower fat foods may also contain fewer calories.

As far as CKD is concerned, the goal is, as AJ Fascetti & S Delaney from the University of California at Davis say in Nutritional management of chronic renal disease, "Your pet needs to consume sufficient calories to supply essential nutrients, as well as to prevent the breakdown of their body's protein stores that will cause malnutrition and exacerbate the clinical signs of uremia."

ISFM consensus guidelines on the diagnosis and management of feline chronic kidney disease (2016) Sparkes AH, Caney S, Chalhoub S, Elliott J, Finch N, Gajanayake I, Langston C, Lefebvre H, White J & Quimby J Journal of Feline Medicine & Surgery 18 pp219-239 state "maintaining calorie intake is the highest priority in CKD."

Therapeutic kidney diets are more calorie dense than standard maintenance diets. You can check the calorie content of some US foods here (canned) and here (dry).

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

The ins and outs of managing feline chronic kidney disease Codi M Today's Veterinary Technician has a formula (Box 1) for calculating the daily energy requirement for neutered CKD cats.

Metabolisable Energy

Some manufacturers provide data about the metabolisable energy (ME) of their foods. ME is the amount of energy available from a food for your cat to use once your cat has digested the food.

 Metabolizable energy and caloric density by PetCoach 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."

ME figures focus on protein, fat and carbohydrate. Since phosphorus is the most important value for CKD cats, I  do not look at ME values when calculating my food data tables, but they may be useful for people with diabetic cats, who often look to feed foods with an ME value for carbohydrates of 10-12% or lower.

Food Composition and Requirements

The usual guidelines for CKD cats are to feed a diet which has added potassium and essential fatty acids but which has reduced levels of protein, phosphorus and sodium. It is helpful to understand the reasoning behind these recommendations. 

Protein

If you asked most people what was the main nutritional step to take for a cat with kidney disease, they would probably say "feed low protein." However, it's not quite as simple as that. This section discusses the role of protein in kidney disease and if and when to reduce the levels of protein which you feed.

• What is protein?

• Feline protein requirements

• Early research into reduced protein for CKD cats

• The upsides of reduced protein intake for CKD cats

• The downsides of reduced protein intake for CKD cats

• Your protein goal: sufficient, high quality protein

• When to feed reduced protein

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

Determining protein requirements — nitrogen balance versus lean body mass (2013) Laflamme DP Nestlé Purina Companion Animal Nutrition Summit Tackling Myths About Pet Nutrition pp42-45 states "The current recommendation by AAFCO for protein in adult cat foods is 26% of the diet dry matter or 65g protein/1000Kcal metabolizable energy. Assuming an average calorie intake of 60Kcal ME/kg body weight for adult cats, this would equate to approximately 3.9g protein/kg body weight. The National Research Council (NRC) guidelines indicate a minimum daily protein requirement and a recommended daily protein allowance of 2.5 and 3.13g protein/kg body weight, respectively."

Let's crunch some numbers based on these recommendations:

• the AAFCO recommendations would mean that a healthy 10lb (4.5kg) adult cat would need a minimum of 18g of protein a day.

• the NRC guidelines would mean that a healthy 10lb (4.5kg) adult cat would need a minimum of 11.4g but a recommended level of 14g of protein a day.

These levels sounded low to me, and research indicates they probably are. Discrepancy between use of lean body mass or nitrogen balance to determine protein requirements for adult cats (2014) Laflamme DP & Hannah SS Journal of Feline Medicine & Surgery 15(8) pp691-7 examined the effects of diets with differing protein levels. The cats in the study were fed a diet containing 34% protein for one month, then they were divided into three groups for a further two months and these groups were fed 20% protein, 26% protein and 34% protein respectively. The study states that "approximately 1.5 g protein/kg (2.1 g/kg(0.75)) body weight is needed to maintain nitrogen balance, while 5.2 g protein/kg (7.8 g/kg(0.75)) body weight is needed to maintain LBM [lean body mass, i.e. muscle]. This study provides evidence that nitrogen balance studies are inadequate for determining optimum protein requirements. Animals, including cats, can adapt to low protein intake and maintain nitrogen balance while depleting LBM. Loss of LBM and an associated reduction in protein turnover can result in compromised immune function and increased morbidity. Current Association of American Feed Control Officials (AAFCO) and National Research Council (NRC) standards for protein adequacy may not provide adequate protein to support LBM. The minimum daily protein requirement for adult cats appears to be at least 5.2 g/kg (7.8 g/kg(0.75)) body weight, well in excess of current AAFCO and NRC recommendations. Further research is needed to determine the effect, if any, of body condition, age and gender on protein requirements."

On this basis, a 10lb (4.5kg) cat would need a protein intake of 23.6g per day. In a study in which cats were not allowed to choose how much they ate, but were able to select the nutrient mix that they preferred, 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." Based on the size of the cats in that study, that actually translated to 5.3g/kg, so very close to the Laflamme calculations above.

To complicate matters, older cats may have higher protein requirements. Skinny old cats: why some senior cats lose weight. What's going on? (2014) Williams D DVM360 Magazine states "Low protein digestibility also seems to affect mature and geriatric cats. Although the incidence of low protein digestibility is lower than that of fat digestibility, about 20% of cats older than 14 years show protein digestibility lower than 77%." 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 prebiotics, antioxidants and essential fatty acids.

PetCoach has an overview of protein requirements in cats.

Early Research into Reduced Protein for CKD Cats

Studies performed on humans and rats with CKD found that feeding reduced levels of protein appeared to be beneficial and might help prolong life. Therefore researchers wondered if a lower protein intake might have a similar beneficial effect for cats.

In many of the early studies in cats, the cats had a large percentage of their kidneys surgically removed in order to induce kidney failure; this is not the way kidney disease tends to develop in most cats, who usually have chronic kidney disease rather than acute kidney injury. Even so, the results were not necessarily what might have been expected. 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 a 38% DMA protein diet or a much reduced (20% DMA) protein diet for one year. The cats fed the 38% protein diet had higher BUN levels (as might be expected) than the cats fed the 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. 

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 functions (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." 

The Upsides of Reduced Protein for CKD Cats

These studies seem to indicate that a reduced protein intake is not necessarily of any real benefit to CKD cats. However, there are also some studies into the use of therapeutic kidney diets, which have reduced protein levels rather than extremely low protein levels (along with other attributes); and more sensibly, research began to focus on cats with naturally occurring CKD. 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 reduced protein, reduced phosphorus therapeutic kidney diet, while a further 21 cats did not eat the therapeutic kidney diet. Some of the cats (presumably in both groups) were also given phosphorus binders. The cats fed the therapeutic kidney 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."

The studies described above were focusing on whether a reduced protein intake might slow the progression of kidney disease and help the cat live longer. The other issue is whether feeding reduced protein might help the cat feel better. The study that most experts cite when recommending a therapeutic 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 therapeutic 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 [creatinine between 2.1 and 4.5 mg/dl or 165 - 400 µmol/L international]."

Thus in this study the therapeutic kidney diet not only appeared to reduce the number of deaths, but the cats also exhibited fewer signs of illness. This is because, 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. Contrary to popular opinion, BUN and creatinine are not toxins themselves. However, BUN levels correlate with uraemic toxin levels, i.e. if BUN is elevated, it is highly likely that toxins are also elevated, and you will usually see various signs of sickness which collectively are known as uraemia.

If you feed a reduced protein diet, this 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. AJ Fascetti & S Delaney from the University of California at Davis say in Nutritional management of chronic renal disease "Many of the clinical signs that you see in your animal such as vomiting, lethargy, anorexia, diarrhea, oral ulcerations and the foul ammonia odor to their breath can be partially or completely alleviated by reducing the protein concentration in your animal's diet. These clinical signs, that are often referred to as uremia, can be caused by an accumulation of the breakdown products of protein metabolism (sometimes referred to as nitrogenous waste products). This protein comes from both the protein in your animal's diet, as well as mobilization and degradation of their own body's protein stores. Consumption of protein in amounts greater than what your animal needs to maintain normal bodily functions can exacerbate these clinical signs."

Nutritional management of chronic renal disease Fascetti AJ & Delaney S also says "A reduction in dietary protein may also help reduce the degree of anemia in some patients. Anemia enhances the weakness and reluctance to eat in animals with renal failure. Anemia can occur for several reasons with renal disease, but one factor that is believed to make it worse is excessive dietary protein. Nitrogenous waste products are believed to contribute to anemia by reducing the life span of red blood cells. The waste products may also enhance blood loss by leading to the formation of gastrointestinal ulcers and a reduction in blood clotting ability."

It must also be remembered that when vets recommend therapeutic kidney diets, they are not only recommending reduced protein levels. Therapeutic kidney diets have other attributes, for example reduced protein diets also tend to contain less phosphorus, and phosphorus control is extremely important in CKD cats. These foods also contain additional levels of potassium and essential fatty acids (see below). You can read more about the attributes of therapeutic kidney diets on the Which Foods to Feed page.

The Downsides of Reduced Protein for CKD Cats

Of course, nothing is ever simple when it comes to cats, so there are also potential downsides with reduced protein intake. One common problem with reduced protein for cats, as you might expect, is weight loss. One study using healthy cats, Determining protein requirements — nitrogen balance versus lean body mass (2013) Laflamme DP Nestlé Purina Companion Animal Nutrition Summit Tackling Myths About Pet Nutrition pp42-45 states "Cats fed lowprotein diets tended to lose body weight to a greater degree than those fed higher protein diets despite no significant differences in energy intake. In study three, for example, only the group fed the highest protein diet had no cats removed owing to weight loss of >10%. In study one, percent weight loss increased in a linear manner with decreasing protein intake."

Feeding cats with different nutritional needs: a dilemma in the multicat household (2012) Scherk M Presentation to the 73rd SCIVAC International Congress 2012 says "Protein:calorie malnutrition occurs when a cat is getting enough calories but not enough of them come from protein. As a result, there may or may not be weight loss, but there will be muscle wasting as well as a deterioration in the hair coat quality. Because protein is component in antibodies, immune function may be compromised; anemia may be exacerbated due to the lack of building blocks for hemoglobin; albumin levels may decrease and tissue healing will be affected. Protein is a preferred flavour, so if a cat is already inappetant, restricting protein may result in inadequate intake of all nutrients, and the protein intake may fall below that required for normal function."

Slowing the progression of chronic renal failure (2004) Grauer GF states "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."

Nutritional management of chronic renal disease Fascetti AJ & Delaney S goes further, and says "not enough protein in the diet can be equally detrimental and protein malnutrition in patients with renal failure can facilitate the occurrence of other complications or lead to an early death."

Cats with IRIS stage 1 and 2 chronic kidney disease maintain body weight and lean muscle mass when fed food having increased caloric density, and enhanced concentrations of carnitine and essential amino acids (2019) Hall JA, Fritsch DA, Jewell DE, Burris PA & Gross KL Veterinary Record 184(6) pp190 compared two dry therapeutic kidney diets (Hill's Prescription Diet k/d with chicken and Royal Canin Renal Support A) fed to cats in IRIS stage 1 or 2. The Hill's food has around 34% protein on a DMA basis whilst the Royal Canin A has around 24%. Cats fed the Hill's food ate more calories, maintained or increased body weight and their kidney bloodwork remained stable, whereas the cats fed the lower protein Royal Canin food lost weight and their creatinine levels rose more quickly. (Most of the researchers who participated in this study work for Hill's). However, the Hill's food was enhanced with essential amino acids, L-carnitine and palatability, which would not be the case if you simply bought this food as a consumer. The study did state that both diets would have provided sufficient amino acid intake if sufficient food and calories were consumed.

Reduced 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, Osborne 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.

Your Protein Goal: Sufficient, High Quality Protein

As discussed previously, 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 your CKD cat may feel poorly. AJ Fascetti & S Delaney from the University of California at Davis say in Nutritional management of chronic renal disease "Many of the clinical signs that you see in your animal such as vomiting, lethargy, anorexia, diarrhea, oral ulcerations and the foul ammonia odor to their breath can be partially or completely alleviated by reducing the protein concentration in your animal's diet...Consumption of protein in amounts greater than what your animal needs to maintain normal bodily functions can exacerbate these clinical signs."

You will note the reference to not feeding more protein than your cat's body needs to maintain normal function. This is the crux of the matter. You do not want to feed an extremely low level of protein so your cat suffers weight loss and malnutrition; but nor do you want to be loading your cat's body with unnecessarily high levels of protein which contribute to your cat feeling ill. The goal in CKD is not to feed low protein or high protein. The goal is to feed sufficient protein with the correct balance and number of amino acids to maintain the cat's health and body weight, but in a form which needs as little breaking down as possible. When talking about CKD, that is what we mean by "high quality protein", not reaching for organic, high quality meat.

The protein goal for CKD cats used to be around 25% protein on a dry matter analysis (DMA) basis. However, because of the potential problems with reduced protein intake outlined above, the goal nowadays is usually a protein level on a DMA basis of 28-35%. This is recommended by Small Animal Clinical Nutrition — 6th Edition, Chapter 37, Chronic Kidney Disease (2019) Davenport D & Kirpensteijn J (Eds.) Mark Morris Institute, which states that "The recommended range for DM protein levels in foods intended for most patients with CKD is 28 to 35% for cats. Foods with less protein may be needed to control signs of uremia in patients with more advanced CKD; in these patients, it’s important to monitor for signs of protein deficiency. In addition to the amount of protein, patients with CKD should receive protein of high biologic value."

For most people, the easiest way to achieve this is to feed a therapeutic kidney diet because these diets have a protein level in this range. This does not mean they are low protein foods. Feeding cats with different nutritional needs: a dilemma in the multicat household (2012) Dr M Scherk Presentation to the 73rd SCIVAC International Congress 2012 says "A note about restricted and high protein diets: these diets do not have too little or too much protein, their protein levels fall within the nutritional guidelines, merely at the low or at the high end of the range.'

Evidence-based medicine: protein requirements in dogs and cats with chronic kidney disease (2017) Ross S Presentation to the 2017 Hill's Global Symposium says "In one commercially available feline renal diet, the protein content exceeds the AAFCO recommendations for crude protein content by 4% dry matter (DM). Additionally, the composition of the protein supplies at least 150% of the daily recommended amounts of 11 essential amino acids."

ISFM consensus guidelines on the diagnosis and management of feline chronic kidney disease (2016) Sparkes AH, Caney S, Chalhoub S, Elliott J, Finch N, Gajanayake I, Langston C, Lefebvre H, White J & Quimby J Journal of Feline Medicine & Surgery 18 pp219-239 state "Feline renal diets typically contain 6–7 g of protein per 100 kcal (above the 5 g/100 kcal recommended allowance for adult cats, but below the 9–10 g/100 kcal commonly seen in maintenance diets). Energy requirements of older (>13 years) cats may increase and severe protein restriction may lead to loss of lean tissue; thus moderate protein restriction is recommended in CKD, together with monitoring of lean body mass, weight and caloric intake." In other words, the protein levels seen in therapeutic kidney diets should be adequate for CKD cats, but you should monitor your cat's weight, muscle levels and calorie intake.

If you find your cat starts to exhibit weight or muscle loss, you could consider trying one of the therapeutic kidney diets with protein at the higher end of the suggested range. Feeding cats with different nutritional needs: a dilemma in the multicat household (2012) Scherk M Presentation to the 73rd SCIVAC International Congress 2012 says "The protein restricted therapeutic diets are not all the same; there are some marked differences in their composition, not just in protein sources and quantities, but also in the calorie source, in their phosphorus, potassium, and sodium content." As mentioned above, Cats with IRIS stage 1 and 2 chronic kidney disease maintain body weight and lean muscle mass when fed food having increased caloric density, and enhanced concentrations of carnitine and essential amino acids (2019) Hall JA, Fritsch DA, Jewell DE, Burris PA & Gross KL Veterinary Record 184(6) pp190 compared two dry therapeutic kidney diets (Hill's Prescription Diet k/d with chicken and Royal Canin Renal Support A) fed to cats in IRIS stage 1 or 2. The Hill's food has around 34% protein on a DMA basis whilst the Royal Canin A has around 24%. Cats fed the Hill's food ate more calories, maintained or increased body weight and their kidney bloodwork remained stable, whereas the cats fed the Royal Canin food lost weight and their creatinine levels rose more quickly. (Most of the researchers undertaking this study work for Hill's. 

Personally I would try to feed a food with a protein level of 35% on a dry matter analysis basis, or as close to this as you can get.

If you are concerned about weight and/or muscle loss, you can also consider adding foods with high biologic value but minimal nitrogenous waste to your cat's therapeutic kidney diet. A good choice would be egg whites.

If you cannot persuade your cat to eat a therapeutic kidney diet (see Which Foods to Feed for tips on how to do this), you can also check the food data tables to find other foods which are relatively low in protein; but don't forget the therapeutic kidney diets have other important attributes, and the protein they do contain is good quality from the CKD perspective, something which is not always easy to replicate with non-therapeutic kidney foods.

When To Feed Reduced Protein

IRIS Stages 1 and 2

Because of the potential downsides of protein restriction, it is not necessarily a good idea to feed reduced protein food in all cases. Treatment recommendations for CKD in cats (2019) International Renal Interest Society divides CKD into stages (see How Bad is It?) and suggests starting a therapeutic kidney diet in Stage 2, i.e. when the cat's creatinine is over 1.6 mg/dl or 140 µmol/L. However for cats with proteinuria, it states "feed a renal clinical diet" regardless of the stage the cat is in.

Positive impact of nutritional interventions on serum symmetric dimethylarginine and creatinine concentrations in client-owned geriatric cats (2016) Hall JA, MacLeay J, Yerramilli M, Obare E , Yerramilli M, Schiefelbein H, Paetau-Robinson I & Jewell DE PLoS One 11(4) looked at feeding a therapeutic kidney diet to cats in IRIS stage 1. The study concludes "Our results suggest that cats with early renal insufficiency fed a test food designed to promote healthy aging, over a 6 month period, were more likely to have stable renal function evidenced by stable serum SDMA concentrations compared with cats fed owner's-choice foods. Cats fed owner’s-choice foods were more likely to have progressive renal insufficiency characterized by increasing serum SDMA concentrations." However, the food fed in this trial was specially formulated and is not commercially available. It is also difficult to compare the effect of the therapeutic kidney diet because not enough is known about the alternative foods that were fed.

Other vets believe that it is better to wait until the disease is more advanced before starting a therapeutic kidney diet. Managing chronic diseases cats (2005) Veterinary Medicine Little S 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. Diet and nutritional management for hyperthyroid cats (2011) Peterson ME (the man who discovered hyperthyroidism in cats) states that "The major problem that I have with some of the prescription kidney diets is that they restrict protein to the point that some cats — especially those with concurrent hyperthyroidism — will continue to catabolize their own muscle mass despite adequate control of the thyroid condition." For cats with both CKD and hyperthyroidism, he states that reducing protein should be avoided in IRIS stages 1 and 2, but that phosphorus control is very important.

Unfortunately, it can often be easier to switch a cat to a reduced protein diet when the cat is stable with lower numbers. Treatment recommendations for CKD in cats (2019) International Renal Interest Society says that introducing a therapeutic diet "may be accomplished more easily early in the course of CKD, before inappetence develops." So if your early stage cat is prepared to eat a therapeutic kidney diet, it is worth trying one, even if initially you don't feed it exclusively. The manufacturers claim that their diets have adequate protein levels for cats at every stage of CKD, but be sure to monitor your cat's weight and body condition, and keep an eye on your cat's albumin levels — Prolonging life and kidney function (2009) Chew DJ & DiBartola SP CVC in Kansas City Proceedings states "Maintenance of stable body weight and serum albumin concentration suggests adequate intake of calories and protein whereas progressive declines in body weight and serum albumin concentration suggest malnutrition or progression of disease and are indications to increase the amount of protein fed." See Which Foods to Feed for more information.

If you are concerned, consider adding foods with high biologic value but minimal nitrogenous waste to your cat's therapeutic kidney diet. A good choice would be egg whites.

If you decide not to feed reduced protein to your CKD cat, please do ensure that your cat has a low phosphorus intake and an increased essential fatty acids intake.

IRIS Stages 3 and 4

As stated above, Treatment recommendations for CKD in cats (2019) International Renal Interest Society divides CKD into stages (see How Bad is It?) and suggests starting a therapeutic kidney diet in Stage 2, i.e. when the cat's creatinine is over 1.6 mg/dl or 140 µmol/L. Cats who are in Stages 3 and 4 would therefore also be advised to eat a therapeutic kidney diet.

Another factor to consider is your cat's BUN level. Since BUN is influenced by protein intake, it does often help the cat feel better if you restrict protein intake as your cat's BUN levels rise. Dr D Polzin states in Chronic kidney disease (2007) Delaware Valley Academy of Veterinary Medicine "Urea, once thought to be “the” uremic toxin, is not a major cause of uremic toxicity, although it may contribute to some of the clinical abnormalities, including anorexia, malaise, and vomiting." Generally speaking, once BUN levels are over 60 mg/dl (urea over 21 µmol/L), you are more likely to see symptoms such as vomiting and nausea, so if you are not already feeding reduced protein, this may be the time to start. 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."

You may panic if you cannot get your cat to eat a reduced protein food. Take a deep breath. Managing chronic diseases cats (2005) Veterinary Medicine Little S 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 reduced protein. See the Which Foods to Feed page for more tips on getting your cat to eat the therapeutic kidney diet and what to do if you can't succeed. Treatment recommendations for CKD in cats (2019) International Renal Interest Society states for Stage 4 cats "Intensify efforts to prevent protein / calorie malnutrition. Consider feeding tube intervention (e.g., percutaneous gastrostomy tube)." If you use such a tube, you can feed a therapeutic kidney diet very easily. See the Persuading Your Cat To Eat page for more information on feeding tubes and tips on getting your cat to eat.

Whatever you do, monitor your cat's weight and muscle status closely.

Phosphorus

Controlling phosphorus levels is extremely important for CKD cats, because 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 wellbeing and can also prolong survival.

Fat

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, a study in which cats were not allowed to choose how much they ate, but were able to select the mix of nutrients that they preferred, found that the fat target for healthy cats is about 9g a day or 36%.

Older cats may process fat less efficiently than younger cats, which may be a factor in weight loss. Skinny old cats: why some senior cats lose weight. What's going on? (2014) Williams D DVM360 Magazine states "The incidence of low fat digestibility increases with age, affecting 10% to 15% of mature cats (8 to 12 years old) and 30% of geriatric cats (> 12 years old). In some geriatric cats, fat digestibility was found to be as low as 30%, and the only clinical signs were large stools (not frank diarrhea) and low body weight."

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. Your cat's nutritional needs (2006) National Research Council states "The maximum amount of fat in the cat’s diet can be reasonably high without any known adverse effects. In many cat foods, 50% or more of the energy comes from fat. Studies indicate that cat foods containing even higher amounts of fat are safe."

Fat has been implicated in the development of obesity in healthy cats, but obesity is hardly a problem for the average CKD cat; in fact, since fat contains twice as many calories as protein or carbohydrate, 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 therapeutic kidney foods, the fat content is increased to compensate for the lower protein levels. According to Nutritional management of chronic kidney disease in cats and dogs (2016) Cline MG Today's Veterinary Practice 6(2), the increased fat content also helps maintain palatability.

Some 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 levels. Therefore, if your cat won't eat a therapeutic kidney diet, it is worth considering senior foods, although do check the protein level is not too low.

Sodium

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."

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."

Effects of dietary salt intake on renal function: a 2-year study in healthy aged cats (2013) Reynolds BS, Chetboul V, Nguyen P, Testault I, Concordet DV, Carlos Sampedrano C, Elliott J, Trehiou-Sechi E, Abadie J, Biourge V & Lefebvre HP Journal of Veterinary Internal Medicine 27(3) pp507-15 compared cats fed a high sodium diet with cats fed the same diet but without the high sodium levels. The study concludes "The results of this 2 year study do not support the suggestion that chronic increases in dietary salt intake are harmful to renal function in older 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."

Sodium in feline nutrition (2017) Nguyen P, Reynolds B, Zentek J, Paßlack N & Leray V Journal of Animal Physiology and Animal Nutrition 101 pp403-420 looked at the role of sodium in cats and states "there is no evidence of any deleterious effect of dietary sodium levels as high as 740 mg/MJ metabolizable energy, which can therefore be considered the SUL [safe upper limit] based on current knowledge."

So should you restrict sodium intake or not? Treatment recommendations for CKD in cats (2019) International Renal Interest Society state 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 reduce your cat's sodium intake, 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

Around 30% of CKD cats have potassium levels which are too low. This occurs because potassium is easily lost through increased urination and vomiting. Therapeutic kidney diets 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 called metabolic acidosis.

If your cat refuses to eat a therapeutic diet, your vet can give you a potassium supplement instead, if appropriate. Some cats need a potassium supplement regardless of whether they eat the therapeutic kidney diet. 

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. 

Please see the Potassium page for more information about potassium.

Carbohydrates

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. In a study in which cats were not allowed to choose how much they ate, but were able to select the mix of nutrients that they preferred, 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, it was found that target intake for carbohydrate in cats was only 8g a day or 12% of total food intake. The study 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 above) rather than the carbohydrates. If you are feeding a therapeutic kidney 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.

PetCoach has an interesting article about carbohydrates in the feline diet.

Fibre

Fibre is the non-digestible component of complex carbohydrate. It is important for good digestive health. Increased fibre may help with elevated calcium levels in the body (hypercalcaemia), although one type of fibre, fructooligosaccharides or FOS, may actually increase calcium levels in the body (see below).

It may also assist with two commonly seen CKD problems, toxin reduction and the control of constipation.

Fibre Types: Fermentable versus Non-Fermentable

There are a number of ways of categorising fibre types, but one way is to divide it into fermentable and non-fermentable.

Which fibres are fermentable depends upon the species of bacteria eating the fibre in the cat's gastrointestinal tract.

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."

Fermentable Fibre for Toxin Reduction

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) Friedman EA 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 in the form of fermentable fibre (prebiotics). 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 may help to reduce the load on the kidneys by diverting the excretion of urea from the kidneys. You can read more about this in the Treatments chapter.

Non-Fermentable Fibre for Constipation

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.

Fibre: Side Effects and Interactions

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 can be a problem for cats who already have high blood 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.

Essential Fatty Acids (EFAs)

• What are essential fatty acids

• Essential fatty acid types

• Essential fatty accids benefits

• Essential fatty acids for CKD cats

• Types of supplement

• Dosage

• Sources

What are Essential Fatty Acids

Essential fatty acids (EFAs) are polyunsaturated fats (sometimes abbreviated as PUFA). They are essential because the cat's body cannot synthesise them in sufficient amounts, so they have to be obtained from food.

Essential Fatty Acids Types

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).

Within the omega-3 category, two common acids are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Arachidonic acid (AA) is an omega-6 type. PetCoach has a very helpful overview of the different types of essential fatty acids.

Qualitative risk assessment of chronic renal failure development in healthy female cats 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 is raised and that of AA is lowered."

Essential Fatty Acids Benefits

Essential fatty acids are important for 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."

A product called 1-TDC which contains essential fatty acids appears to improve periodontal disease in cats. See Dental Problems for more information.

Essential Fatty Acids for CKD Cats

Research in rats and humans indicates that the addition of omega-3 fatty acids to the diet may delay the progression of CKD. Oxidative stress and chronic kidney disease (2008) Brown SA The Veterinary Clinics of North America. Small Animal Practice 38(1) pp157-66 added essential fatty acid supplements in the form of fish oil to dog foods. It concludes "newer data indicate that dietary supplementation with specific antioxidants is an important consideration for limiting renal oxidant stress and progression of CKD."

EFAs may also be of benefit to CKD cats. Nutritional management of renal disease: an evidence-based approach (2014) Sanderson SL Today's Veterinary Practice 4(1) pp51-56 states "When nephrons are destroyed in CKD, the remaining viable nephrons hypertrophy in an attempt to compensate, resulting in a maladaptive increase in glomerular capillary pressure (GCP). Dietary omega-3 fatty acid supplementation in the form of fish oil can have beneficial effects in reducing GCP."

However, Nutritional management of renal disease (2008) Sturgess K Presentation to the World Small Animal Veterinary Association World Congress 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.  This ties in with what one kidney specialist vet has informed me, that oversupplementation can throw off the correct ratio of omega-3s to omega-6s, and might be detrimental in some cases.

Potential adverse effects of Omega-3 fatty acids in dogs and cats (2013) Lenox CE & Bauer JE Journal of Veterinary Internal Medicine 27(2) states "Important potential adverse effects of omega-3 fatty acid supplementation include altered platelet function, gastrointestinal adverse effects, detrimental effects on wound healing, lipid peroxidation, potential for nutrient excess and toxin exposure, weight gain, altered immune function, effects on glycemic control and insulin sensitivity, and nutrient-drug interactions."

Omega-3 fatty acid supplementation for dogs and cats with heart disease (2014) Nutrition Service at Cummings Veterinary Medical Center at Tufts University states "Potential risk factors include decreased platelet function and coagulation, and possibly suppressed wound healing...Other potential effects include soft feces, diarrhea, flatulence, vomiting, and halitosis."

Nutrition and renal function: effects of dietary lipids on renal function (1999) Polzin  DJ, Osborne 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."

The study which has led many vets to look positively at the use of essential fatty acids in cats, 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 therapeutic 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.

Therapeutic kidney foods have an increased level of essential fatty acids compared to standard cat foods, so if you are feeding such a food, supplementation may not be necessary. If you wish to give additional essential fatty acids, ask your vet if they are appropriate for your cat.

Almost everybody I know of who has added essential fatty acids to their cat's treatment plan, whether in a therapeutic kidney diet or as a supplement, has been happy with the results, reporting an improvement in general wellbeing. Additional EFAs do cause vomiting in some cats though, and I've heard from a number of people whose cats had pancreatitis and who felt essential fatty acids did not agree with these cats, causing problems such as diarrhoea. Potential adverse effects of Omega-3 fatty acids in dogs and cats (2013) Lenox CE & Bauer JE Journal of Veterinary Internal Medicine 27(2) states "Pancreatitis also is a concern when feeding high fat diets or high doses of fatty acid supplementation, especially in dogs with a known risk of pancreatitis. However, there are no reports of omega-3 fatty acid or fish oil supplements causing pancreatitis in dogs, cats, or humans. Theoretically, omega-3 fatty acids could prevent pancreatitis because of decreased blood triglyceride concentrations. An extremely high dosage of omega-3 fatty acids or a fish oil supplement in addition to a very high fat diet would likely be required to induce pancreatitis." It goes on to say "Clinical patients that develop diarrhea or other adverse gastrointestinal effects may need a decreased dosage of omega-3 fatty acids as well as other dietary modification."

Essential Fatty Acids: Supplement Types

Fish Oil

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).

Oils from the liver, such as cod liver oil, are not suitable because they contain too much vitamin A and D. Omega-3 fatty acid supplementation for dogs and cats with heart disease (2014) Nutrition Service at Cummings Veterinary Medical Center at Tufts University states "We also recommend avoiding cod liver oil for this purpose as it is too high in vitamins A and D when administered at this dose and can cause toxicity of these vitamins."

Look for an oil pressed from the flesh only and containing EPA and DHA.

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. Many products, especially veterinary ones, already contain vitamin E in an appropriate dosage (it may be referred to as tocopherol), in which case you do not need to supplement Vitamin E.

If for some reason the product you buy does not contain vitamin E, AAFCO PFC Committee Report/Minutes (2015) states on page 16 "Add 10 IU Vitamin E above the minimum concentration for each gram of fish oil per kilogram of diet." (The link also gives the minimum concentration). However, I would ask your vet how much to give, because too much vitamin E can be dangerous. 

Astro's Oil Advanced Renal Care Formula

Astro's Oil Advanced Renal Care Formula, previously called Astro's CRF Oil, is a fish oil-based supplement which was created by a human doctor to treat his own CKD cat. It 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 (which you need to add when you are supplementing fish oils, but which is also an antioxidant) and CoQ10 (ubiquinol), also an antioxidant, but in a concentrated formula. There is more information about it in the Treatments section.

Krill Oil

Some people prefer to give krill oil to their cats because they find their cats tolerate it better. Krill oil is made from crustaceans rather than fish and contains additional antioxidants called astaxanthin and canthaxanthin. Studies have indicated that these antioxidants may inhibit cancer and bacterial infection in mice but Astaxanthin uptake in domestic dogs and cats (2010) Park JS, Kim HW, Mathison BD, Hayek MG, Massimino S, Reinhart GA & Chew BP Nutrition & Metabolism 7:52 pp1-8 states that "domestic dogs and cats fed astaxanthin generally showed different biokinetic profiles when compared to humans and other species. Whether astaxanthin supplementation can modulate immune and anti-inflammatory/antioxidative function remains to be elucidated."

The essential fatty acids in krill oil are phospholipids (in fish-based oils they are triglycerides). I do not know for sure if this has any implications for phosphorus levels in CKD cats but a later study in rats, Feeding different omega-3 polyunsaturated fatty acid sources influences renal fatty acid composition, inflammation, and occurrence of nephrocalcinosis in female sprague-dawley rats (2013) Gigliotti JC, Benedito VA, Livengood R, Oldaker C, Nanda N & Tou, JC Food and Nutrition Sciences 4 pp125-136 concludes "In contrast, rats consuming KO [krill oil] and to a lesser extent FO [flax oil] showed evidence of renal calcification and tubulo-interstitial injury. This was due to increased urinary P excretion associated with the phospholipids content of these oils sources. Although further studies are needed, susceptible individuals should be aware of a potential risk of increasing phospholipids consumption on renal health."

Personally, I think I would be more comfortable using fish oil.

If you are in Europe, especially Italy, you may be offered a new product called Nefrokrill, which contains potassium citrate, lanthanum carbonate (a phosphorus binder) and essential fatty acids. You can read more about it here.

Vegetable-based Oils

Vegetable-based oils, such as coconut oil or olive oil or flax seed (linseed) oil, are not recommended, because they do not contain the essential fatty acids which a cat needs. 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."

Others go further. Omega-3 fatty acid supplementation for dogs and cats with heart disease (2014) Nutrition Service at Cummings Veterinary Medical Center at Tufts University states "Flaxseed/flaxseed oil also are high in omega-3 fatty acids but are ineffective for providing omega-3 fatty acids to dogs and cats so should be avoided."

Essential Fatty Acids Dosage

It can be a bit tricky working out an appropriate dose of essential fatty acids for cats. The National Research Council gives an upper limit for dogs but gives no upper limit for cats.

Fish Oils Dosage

Pet MD discusses the dangers of giving too much but says with reference to the NRA recommendations for dogs, "Translating the data suggests that a dose between 20-55mg combined EPA and DHA per pound of body weight is safe for dogs and cats. This dose is far less than those used to treat serious conditions where the risk of side effects is less important."

Top 5 therapeutic uses of omega-3 fatty acids (2015) Chandler ML Clinician's Brief Feb 2015 pp78-80 states "the amount to supplement is somewhat empiric and depends on the amount in the diet. Common recommendations are 40 mg/kg EPA plus 25 mg/kg DHA, but the amount in studies also varies."

Potential adverse effects of Omega-3 fatty acids in dogs and cats (2013) Lenox CE & Bauer JE Journal of Veterinary Internal Medicine 27(2) states "Target ranges for EPA and DHA vary quite widely for different conditions, but typically fall between 50 and 220 mg/kg body weight. The higher dosages often are used to lower serum triglyceride concentrations in patients with hypertriglyceridemia, whereas lower dosages are more commonly used for inflammatory conditions, renal disease, and cardiac disease."

As far as cats with heart disease are concerned, Omega-3 fatty acid supplementation for dogs and cats with heart disease (2014) Nutrition Service at Cummings Veterinary Medical Center at Tufts University states "The dose of omega-3 fatty acids we currently recommend for dogs and cats with heart failure is 40 mg/kg eicosapentaenoic acid (EPA) + 25 mg/kg docosahexaenoic acid (DHA) per day. There are a small number of commercial pet foods that contain this dose (for example, the Royal Canin Early Cardiac Diet for Dogs). However, in most cases, supplements are needed to achieve this dose."

As you can see, there is no definitive dose, and many of the recommendations relate to a particular amount of EPA (eicosapentaenoic acid).

• One commonly used dose on Tanya's Feline CKD Support Group is 22mg of EPA per kg of cat per day (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; this is more than double the earlier dose.

You will need to check the product you are 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.

I expect your head is spinning by now! Generally speaking, it is probably safe to give your cat one 1000mg fish oil capsule daily. Do check with your vet first though. Therapeutic kidney diets contain increased amounts of EFAs, so if your cat is eating such a food, you may not need supplementation, or may need a reduced dose.

Krill Oil Dosage

The dosage for krill oil (which is made from crustaceans rather than fish) is 500mg per day.

If you are using Nefrokrill, the dosage is here.

Essential Fatty Acids: How to Give

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 taste, and gradually increase the dose over several days or even weeks. If your cat still hates it, you can either 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. If you don't see any difference, or if your cat seems to react badly to them e.g. increased vomiting, speak to your vet about stopping them.

Essential fatty acids can easily go off (they become rancid). Store them in the fridge, and be sure to sniff them before giving them to your cat.

Essential Fatty Acids: Where to Buy

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. Look for pharmaceutical grade products (these are usually steam distilled) that are odourless if possible. If your cat doesn't like the brand you buy, you may need to shop around to find one that is acceptable.

If for some reason the product you buy does not contain vitamin E, AAFCO PFC Committee Report/Minutes (2015) states on page 16 "Add 10 IU Vitamin E above the minimum concentration for each gram of fish oil per kilogram of diet." (The link also gives the minimum concentration). However, I would ask your vet how much to give, because too much vitamin E can be dangerous. 

USA

Brands Overview

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

Omega-3 fatty acid supplementation for dogs and cats with heart disease (2014) Nutrition Service at Cummings Veterinary Medical Center at Tufts University recommends particular brands for cats and dogs with heart disease.

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, but you need to be a member to read it.

Fish Oils

Welactin is a veterinary product available in both softgel capsules and pump bottle. The ESA quantities have changed recently. One capsule contains 125mg EPA and 85mg DHA. One pump contains approximately 1.25 ml and provides 160mg of EPA and 105g of DHA.

Nordic Naturals Omega-3 Pet is based on anchovies and sardines and is a popular choice on Tanya's CKD Support Group. It costs US$15.95 direct from the manufacturer. It is also available from Pure Formulas for US$11.53 with free shipping. You can often find it on Amazon but a couple of members of my support group have found it does not seem to last too well when purchasing it there.

Iceland Pure Unscented Sardine-Anchovy for Pets is also popular. It is available from Chewy for US$24.04.

Bonnie and Clyde Wild Omega-3 is a Canadian brand used by a number of Tanya Support Group members. It is also available from Healthy Pets for US$32.99.

Sundown Naturals Fish Oil is available from CVS. It is 1000mg with total EPA and DHA of 300mg.

Grizzly Salmon Oil is made from wild Alaskan salmon.

Krill Oil

Now Neptune is available from Amazon for US$30.14 for 120 capsules. If you are in Canada, 60 softgels are available from Healthy Planet Canada for CAN$37.99.

Canada

Nordic Naturals Omega-3 Pet is available from iHerb  for CAN$18.86. iHerb will ship to many other countries.

Bonnie and Clyde Wild Omega-3 is a Canadian brand used by a number of Tanya Support Group members. It is widely available in Canada.

Now Neptune krill oil 60 softgels are available from Healthy Planet Canada for CAN$37.99.

UK

Nordic Naturals Omega-3 Pet is a popular choice on Tanya's CKD Support Group. It is available from Amazon UK for £24.99. A couple of members of my support group have found it does not seem to last too well when purchasing from Amazon in the USA but I have not had any complaints about buying it from Amazon UK.

Your vet may also have a suitable product in stock.

Amino Acids

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. The ones which the cat cannot manufacture are called essential amino acids. Taurine is one example of an amino acid which cats must obtain from food. PetCoach has some information about essential amino acids for cats. The protein paradigm: assessing dietary protein in health and disease (2015) Shmalberg J Today's Veterinary Practice 5(6) has some good information about amino acids.

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).

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 acid 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.

There are a couple of amino acid supplements that are marketed for CKD cats. There is more information about them on the Holistic Treatments page.

Taurine

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. 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." A lack of sufficient taurine in a cat's diet can cause blindness and a type of heart disease called dilated cardiomyopathy.

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.

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."

Metabolic acidosis may affect taurine levels. Acid-base, electrolytes and renal failure (1999) Polzin DJ, Osborne CA, James K Supplement to Compendium on Continuing Education for the Practising Veterinarian 21 11(K) states "Studies on the effects of dietary acidification in cats have revealed that chronic metabolic acidosis can cause negative potassium balance, which may in turn promote...taurine depletion."  

There is plenty of taurine in all cat foods, and an even higher level in therapeutic kidney diets. However, some people do choose to give taurine supplements to their CKD cats (a taurine supplement is usually essential if you are feeding a homemade diet). Taurine is water soluble, so any excess should be urinated out, but if you do supplement taurine, check with your vet first — 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 CKD 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.

Pet MD has some information about taurine deficiency in cats.

Arginine

Another 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 Focus on Felines 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, so it is possible that supplementing this might increase nitrous oxide levels and thus help kidney function. 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.

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

L-Lysine

L-lysine is sometimes recommended for cats with feline herpes (cat flu). Lysine for management of herpes labialis (2001) Tomblin FA & Lucas KH American Journal of Health-System Pharmacy 58(4) pp298-304 says "L-lysine poses few safety concerns. Two potential contraindications include renal and hepatic disease in which patients may have difficulty eliminating the large amounts of nitrogen generated from l-lysine metabolism."

L-Carnosine

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.

Vitamins

If your cat is eating a therapeutic kidney diet, 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 and what they are eating, 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.

• vitamin A

• vitamin B

• vitamin C

• vitamin D

• vitamin E

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

Vitamin A

This vitamin is fat soluble, and is stored in the body rather than excreted. For this reason, there is a risk of toxicity when supplementing it. Hypervitaminosis A-induced hepatic fibrosis in a cat (2014) Guerra JM, Daniel AG, Aloia TP, de Siqueira A, Fukushima AR, Simões DM, Reche-Júior A & Cogliati B Journal of Feline Medicine & Surgery 16(3) pp243-8 states "the cat is particularly susceptible to chronic vitamin A toxicity." Vitamin A also promotes calcification, which is a risk with CKD cats because they have a tendency towards calcification anyway.

Omega-3 fatty acid supplementation for dogs and cats with heart disease (2014) Nutrition Service at Cummings Veterinary Medical Center at Tufts University states "Humans with renal failure have a reduced capacity to excrete vitamin A, and although no similar information exists in dogs and cats, the feeding of supplements containing vitamin A is not recommended."

In any event, a vitamin A deficiency is extremely rare, so it is highly unlikely that your cat requires supplementation of any kind. For this reason care should be taken when considering the use of multi-vitamin tablets, which may contain vitamin A.

How can uremic anorexia  be minimized? (2003) 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 (i.e. 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 the excess urination commonly seen in CKD cats. Cats who are not eating much will also probably not be taking in enough B vitamins. Pharmacological appetite stimulation: rational choices in the inappetent cat (2014) Agnew W & Korman R Journal of Feline Medicine & Surgery 16(9) pp749-56 says "Cats have a higher requirement for some B vitamins when compared with dogs. Experimental depletion of B vitamins results in anorexia in other species. Supplementation with B vitamins may prevent this occurring, although no evidence exists to confirm this. Still, provision of B vitamins is simple and should be considered in all inappetent cats."

Skinny old cats: why some senior cats lose weight. What's going on? (2014) Williams D DVM360 Magazine states "more than 90% of cats with serum cobalamin less than 100 g/L have low fat digestibility.^"

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

Vitamin C

Antioxidants may be useful for CKD, and Dietary supplements of vitamins E and C and beta-carotene reduce oxidative stress in cats with renal insufficiency (2006) Yu S, Paetau-Robinson I Veterinary Research Communications 30(4) p403-13 found that using these vitamins as antioxidants appeared to be effective.