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My Vet Says My Cat Or Dog Needs A Special Kidney Diet

Tell Me About That And My Options

 

Ron Hines DVM PhD

 
I have a deep respect for Mary Straus and her DogAware Website. You can read her comments on this article here
 

 

If you reached this page from my 2018 updated kidney treatment page, you already know about the tests and medications that veterinarians use to try  to slow the kidney decline that so commonly occurs as our dogs and cats get older. If not, you can read about that here.

 

 

The medications and life style changes I mention there all try to limit the effects of the inflammation, oxidative stress, scaring (fibrosis) and toxins that build up when a dog or cat’s kidneys begin to loose their ability to perform their duties.  We believe that those treatments can be effective in slowing the progress of chronic kidney (renal) disease (CKD). But there are non-drug options too. Adjusting the nutrient content of you pet’s food might lessen the workload on its kidneys as well.
You all know that dogs and cats are carnivores - their teeth tell you that. Both experience great pleasure eating meat, and, given the choice, will consume meat to the exclusion of many of the ingredients us humans commonly enjoy eating.  That’s just fine when they are kittens and puppies and in their healthy adult years. (ref)
That was what Nature intended; what it designed their metabolism to thrive on. But when time starts to take its toll on their kidneys, many veterinarians and nutritionists believe these pets could gain a bit more time on this earth if their diet was adjusted to lessen their kidney’s chores. Of course, your pet does not think of it that way, it lives in the here and now and does not contemplate tomorrow. 

Are Cats And Dogs Different In Their Nutritional Needs ?

Yes, they are quite different.
Cats have not made the genetic nutritional adjustments to domestication that many dogs have. Despite what pet food companies stuff into cat foods and what owners feed their cats, felines have extraordinarily high protein needs and they prefer that protein to be meat. Ownerless (feral) cats are free to choose what they can catch and eat. They consume about 52% protein and 46% fat. Only a very small amount is carbohydrate (~2% - most of it coming from eating stored liver and muscle glycogen)  (ref) The cat’s normal rodent diet is about 66% water. With such a protein-rich diet, there was no need for them to retain many of the enzyme and metabolic pathways that we omnivores (or even dogs) possess. (ref)  The consequence is that felines rely on their prey to furnish many nutrients that us humans and dogs can manufacture in our bodies. (ref)
Another consequence is that one cannot restrict the protein intake or up the carbohydrate intact of  cats  nearly as much as one can in dogs or humans without causing them great metabolic distress. (ref)

Given their druthers, most cats will eat about 6 grams of protein per kilogram of their body weight per day. (ref) Earlier studies, used by AAFCO and the NRC underestimated the amount of protein cats truly need and what the consequences of not providing it could be. (ref) There is also quite a bit of evidence that crosses species lines that otherwise-healthy animals require more, not less, protein as they age. (ref1, ref2 Most healthy adult dogs can thrive on considerably less protein than cats. That is because cats must metabolize (“burn”) a great deal of the protein they eat to meet their energy needs. But dogs, in their journey to domestication, have acquired a much greater ability to digest and utilize carbohydrates. That has led some to suggest that they can subsist on diets that have protein levels as low as 16% (ref) - although the NRC keeps their minimum at 20% and AAFCO at 22.5% for good measure.
However dog breeds are quite variable when it comes to their genetic requirements for protein. A few remain true to wolves in their high protein requirements. But over their ~15,000 association with humans, many breeds have mutated from wolves in their diet as well as their temperament and have increased their ability to thrive on the same high-carbohydrate diets that their owners consume. In 2013, a group of Swedish scientists tried to discover the genetic changes that allow them to do that. They found that dogs had considerably more ability to digest carbohydrates due to gene changes that increased the levels of their amylase digestive enzymes.  They found that ability varied between breeds. In some, the ability to produce amylase was 30 times greater than in wolves. In other breeds, it was only 4 times greater. You can read their report here.
In conversations with the authors a number of years ago, they told me that the Arctic breeds, those that might have been later to be domesticated or exposed to the same highly carnivorous diet as arctic-dwelling humans seemed less able to digest carbohydrates and starches. They sent me some supplemental information. (ref)

When one attempts to tinker with the carbohydrate content of a dog’s diet, one ought to keep in mind that in some dogs are more similar to cats in their lack of ability to digest and utilize starches and sugars.

What Are Veterinarians And Nutritionists Hoping For When They Suggest That Your Cat or Your Dog Begin A Special Kidney Diet ?

They are hoping that moderating the amount of protein and phosphorus in your pet’s diet will lessen its kidney workload. They are hoping that additional ingredients like omega-3 fatty acids and antioxidants might lessen kidney inflammation (despite controversies as to their effectiveness). They are hoping that reduced salt in these diets will control kidney blood pressure. They are hoping that added vitamins that might be in short supply will help slow kidney decline.  The general opinion among veterinarians in 2018 is that these diets are probably helpful. (ref) Dean2015.pdf  - although how helpful, at what point they should start to be used and their optimum dose is still a matter of debate.

Might Lowering My Pet’s Protein Intake Be A Good Idea When CKD Is Present ?

First off, I said lowering protein, not low protein. The major brand commercial “kidney health” diets are thought to contain more than enough protein to meet the nutritional needs of your adult cat or dog. (ref) They would not sell them if they did not believe that to be so. Home made diets for cats (and dogs) can also be considerably higher in protein than pets are thought to require. Excessively high meat-protein diets are always very high in phosphorus as well. (ref)

Most believe that truly low protein diets are never a good idea until, perhaps, the terminal stages of kidney failure and I am not sure I would consider using them even then. It has been found that truly low protein diets tend to speed the animal’s rate of decline. But providing dogs and cats with kidney disease with no more protein than they require to remain healthy seems like quite a good idea. (ref)

The many commercial “kidney health” diets you see advertised (Hills, Royal Canin, Purina, Eukanuba) have only moderately reduced protein levels. There are also a lot of smaller players in the veterinary diets market whose products and nutritional adequacy I know nothing about. If you elect to give your pet a “kidney health” diet, I believe you are safer using a product produced by one of the larger players where board certified veterinary nutritionists are making ingredient decisions. (ref)

Even veterinary nutritionists need hard, reliable data to make decisions as to what would be best to feed your cat or dog. But when it comes to protein levels and sources and their effect on your pet’s kidneys, studies returned conflicting results.  There were two early camps conducting studies as to the effect of dietary protein levels on kidney health. The first was located at the veterinary school at the University of Georgia in Athens. (ref) The second was located at the veterinary school at the University of Minnesota, St. Paul. One was in dogs. (ref)   One was in cats. (ref) You can read another of the Minnesota studies here: (ref)

The two groups reached opposite conclusions. The Athens group presented data that seemed to show that lower protein diets sped the demise of dogs and cats; while the Minnesota studies found the opposite. You can read the other Georgia studies here: (1, 2, 3, 4). Others agreed. (ref)

The conflicting results of those two groups perplexed me for years. Three things caught my attention.  In the Minnesota studies, the dog and cats that were fed the higher protein diet appeared from their lab work to have been considerably sicker than the ones fed the lower protein diet. Blood creatinine levels in the higher protein group were worse in the dogs and cats before the studies began than they were in the lower protein groups.  Another thing that caught my eye was that the two diets differed in several ways besides their protein content: their omega-3, and phosphorus contents was also different. The last thing that caught my eye was the funding source for the Minnesota studies. They were financed by Hills – the manufacturer of the lower-protein diet used in the study.

Company-funded studies performed at institutions of learning are never good way to get unbiased conclusions. (1, 2, 3, 4 By their nature, profit-based corporate motivations can never be evenhanded.  It’s basic human nature for all of us to want to reciprocate positively when a benefactor gives us something of value. The Minnesota kidney studies were never repeated, never independently confirmed. Never-the-less, they remain the lynch-pin studies that defines most veterinary thinking on the positive role of reduced protein in pets with CKD (chronic kidney/renal disease) to this day (rptref1, ref2)  The form the basis of a tremendous advertising campaign designed to convince veterinarians and pet owners alike of the value of their products. (ref)

Regarding the Georgia studies: They were performed at a time when sacrificing dogs for the sake of scientific knowledge was considered desirable and proper. But in these studies, the sudden surgical loss of 7/8th of their kidneys was quite different from the gradual loss of kidney function that our pets experience.  You can read the opinion of a respected veterinary nephrologist who was, at various times in his career, at both the MINN and GA facilities here.

Reading the protein content of your pet’s food can be deceptive. For instance, a Purina Adult formula dog chow with 21% protein can not be compared to a Purina NF with Purina NF Kidney Function™ “kidney health” dog chow with a  12% protein level because in that second formula, the protein sources are of much higher quality. The same goes for a Hills Science diet for cats with a protein level of 35.5% where the chief protein ingredient is chicken.  compared to a Hill's® Prescription Diet® k/d® with a  protein level of 31.1% where the chief protein ingredient is Corn gluten. The absorbable amount of phosphorus in the gluten meal is considerably less than in the chicken and the protein absorbability and profile is different. (ref) Funaba2005.pdf

How Does The Protein My Pet Eats Affect Its Kidneys ?

It does so in two ways:

First, absorbed protein increases blood pressure within the tiny capillaries that form your pet’s kidney filtering unites (the glomeruli  ) image glomerulus.jpg
Because this increased pressure causes more blood to be converted into urine through each glomerulus, it is called hyperfiltration. Hyperfiltration is thought to be damaging to kidneys and one cause of protein leakage into the urine (proteinuria). Early in kidney disease, lower dietary protein levels may keep that pressure in check. But as CKD progresses, your veterinarian might prescribe medications like ACEi s   and ARB s
to reduce blood pressure and hyperfiltration even more. (ref1, ref2, ref3, ref4)

The second thing that high dietary protein does is release more metabolic wastes into your pet’s blood stream as it is broken down. It is the kidney’s job to filter out those waste products from your pet’s blood stream and deposit them in its urine. Failing kidneys are not good at doing that; so these toxic waste products build up in the animal’s system. (rptref)

I do not want you to view protein as your pet’s enemy. An adequate amount of protein is essential in your dog or cat’s diet to replenish the amino acid building blocks of its body.  Through the early 1980s, human nephrologists believed that truly low protein diets would slow the progress of kidney disease in their patients. But in the late 1980s, NIH began to fund studies to see if that was really the case. (ref)   They were called the Modification of Diet in Renal Disease (MDRD) studies. When the results were finally published in 1994, they had found that there was, perhaps, a slight benefit to the patients eating the low protein diet in the early stages of CRF (ref1, ref2)   But in the later stages of the disease, patients on truly low protein diet often seem to do worse. Today, we know that older folks may need even higher amounts of protein in their diets. (ref)   The results of the MDRD studies caused a lot of grumbling in the ranks. Some physicians agree, (ref), some do not. (ref1, ref2, ref3, ref4)

Although kidneys perform the same general duties in all mammals - dogs, cats, rats, humans - nutritionists point out the dangers in assuming that low protein diets will affect all of them the same ways. They are right about that. I only brought up the human studies to show you how difficult it is to decide when and if a pet’s dietary protein level should be reduced.  Perhaps doing so will help, perhaps it won’t, perhaps it depends at what stage of CKD one begins to lower it. Perhaps the dynamics of CKD in one pet favors reducing its dietary protein level while the dynamics of CKD in another pet does not. (ref1, ref2) Perhaps DeepMind will some day figure it out.

Is Lowering My Pet’s Phosphorus Intake A Good Idea ?


I believe that more veterinary kidney specialists agree that lowering your pet’s phosphorus intake is the prime beneficial effects of “kidney health” diets than believe that it is lower protein levels that provide the beneficial effects. The main dietary source of phosphorus in traditional pet foods is meat protein. (rptref) So when you feed a diet with less protein, you are feeding a diet with less phosphorus as well. (ref)

Phosphorus does not float freely in your pet’s body or blood. It is combined with other elements to form phosphates (PO4). Most of it (~85%) resides in your pet’s bones where it is linked to calcium in the form of hydroxyapatite. Phosphorus is the second most abundant mineral in your pet’s body. Much smaller amounts of phosphorus occur within all cells of your pet’s body where they are linked to other compounds that are important in maintaining cell structure (phospholipids) and energy production (eg ATP). When laboratories report the amount of phosphorus (P) in your pet’s blood, they report it in its pure, uncombined form – not as it actually exists in your pet’s body. Many use the terms phosphorus and phosphate interchangeably.

It is the job of your pet’s kidneys to keep phosphorus levels in the body optimal. When too much is present, it is excreted into the urine. When P levels are low, most that escapes through the kidney’s glomeruli filters is reabsorbed farther down by the cells that form the urine channels (renal tubules).  (ref)   Dogs and cats on standard pet foods consume many times more phosphorus than they require, so most of the time, their kidneys spend their time removing phosphorus.

Abnormally high blood phosphorus levels (hyperphosphatemia) in your pet is detrimental in many ways. The most notable effect is on your pet’s parathyroid gland. Phosphorus stimulates the release of more parathyroid hormone (PTH).That reduces calcium absorption from food, which decreases bone strength throughout the body.  Nausea vomiting and lack of appetite that sometimes accompanies high P was thought to be one of the reasons pets with CKD loss weight. But high phosphorus levels might actually directly affect the animal’s muscles in negative ways. (ref) It appears that very small increases in blood phosphorus levels – perhaps even levels in the high “normal” range – can be detrimental over time. (ref)

In 1991, the same Georgia group that did the protein studies in dogs designed an experiment to test the effects of a low-phosphorus diet on kidney failure. Some of the dogs were feed a ~17% protein diet with a standard phosphorus content and the others the same diet with a 70% lower phosphorus content. At the end of 24 months, 75% of the dogs on the low phosphorus diet still survived; but only 33% of those receiving the higher phosphorus level diet were still alive.  You can read that article here, or in a second publication which I believe describes the same study here.  

Now there are risks in restricting your pet’s phosphorus intake by simply restricting the amount of protein it its diet. Human nephrologists found that out as well. (ref)   They call the problem protein-energy wasting. (ref) But there are other approaches to getting less phosphorus. First, the phosphorus in plant protein is not absorbed from your pet’s intestine as easily as the phosphorus in meat protein. Plant proteins contain compounds called phytates. Some consider them antinutrients  and avoid them. But phytates have a good side too. They inhibit the absorption of a lot of the phosphorus present in plant protein. Phytates will decrease the absorption of calcium in the diet too - so nutritionists add extra calcium. The veterinary nutritionists employed by the major pet food manufacturers know all about phytates. That is why, if you check the ingredients labels on their “kidney health” diets, corn or wheat gluten meal and/or soybean meal, are high on the protein ingredient list. They also get around these somewhat lower quality protein sources by fortifying the diets with higher "quality" (more available amino acids) meat or egg white ingredients. (ref) One Ohio State veterinarian with an interest in kidney disease estimated that through these manipulations, renal-friendly veterinary diets are able to reduce phosphorus absorption by 70-80% over standard grocery store petfoods. (ref) I do not know if that has been confirmed, but renal diets are certainly lower in absorbable phosphorus.

The amount of phosphorus that your pet absorbs from its diet can also be reduced considerably by giving the phosphate binders I discussed in my CKD treatment article. (ref)   In cats that will accept them, these binders have been reported to be particularly helpful in extending their lives. (ref) Phosphate binders are standard treatment in late-stage human kidney failure as well. (ref)  Besides the pharmaceutical binders commonly dispensed, the processed shells of crabs and shrimp (chitins) seem to have this ability as well.  (ref) It it is one of the ingredients in Pronefra™ Virbac's liquid phosphate binder.

What About The Fat Content of My Pet's Diet ?

Dogs and cats are quite good at utilizing fat to meet their energy needs. Whole beef carcasses are about 30-35% fat - although the meat products used in pet foods are lower. The nutritionists who design the kidney health diets you see advertised keep their fat content high. That allows them to lower the protein content of the diets while still providing enough caloric energy and taste appeal. Although the makers of these foods say that in multi-pet households, all the pets can consume the same renal diet, we really do not know what the long-term feeding of these diets to healthy dogs and cats might do. Veterinarians know that otherwise-healthy older pets actually need more protein and less caloric fat energy, not the reverse. (ref1, ref2, ref3, ref4)

That is why I would prefer you feed these high fat diets to your pets with kidney issues separately from your other pets if that is at all possible. Feeding these high-caloric diets to normal or early stage CKD pets might allow a pet owner to mistake an overly chubby pet for one with acceptable lean body mass. That is something you would want to avoid.  At least in laboratory rodents, high fat diets are no friend of the kidneys. (ref) But then, rodent were designed to eat a much lower fat diet.

When Should My Dog Or A Cat Begin A Lower Protein, Lower Phosphorus Kidney Diet ?

I personally would not begin my pet on one of these diets until your veterinarian saw clear evidence that the pet’s kidneys were under stress. Things like beginning elevations of  blood creatinine and BUN level (=azotemia), persistent elevated urine albumen protein or elevated blood phosphorus levels. Now there are plenty of veterinarians and all of the manufacturers of these products who will suggest you begin these diets sooner – even on the basis of the perfidious SDMA. Luckily, the major manufacturers have constructed their recipes so that cats with healthy kidneys could probably do quite well on them too. Only Purina NF flirts with really low protein levels. But since it is given as a minimum value (12%) not the maximum level, I really do not know how low it really is. Dogs and cats get a lot of pleasure from eating meat. It is their natural diet.  I would not deprive them of that, particularly when the evidence that it might help their kidneys earlier in the disease is so meager.  Absent the above blood and urine changes, I most certainly would not begin those diets based on a high SDMA test

Fed these diets, your pet’s creatinine, BUN and SDMA levels are probably going to go down. But that can be just because the amount of protein they are consuming in those diets is less. It happens in a healthy dog and cats with no kidney issues when they eat less protein. There is just less protein wastes to dispose of. If these drops have anything to do with positive benefits to their kidneys is something we do not know. Some do not acknowledge this. (ref1, ref2)  What would warm my heart most would be an increase in your pet's thin, lean muscle body weight as well as greater energy levels.

Other Than Lower Protein And Lower Phosphorus, What Other Nutrients Might Be Helpful Or Harmful To My Pet With Kidney Disease ?

Salt

Most of the drive to keep salt (sodium) intake down in pets with CKD comes from studies that confirm that high salt intake in rats and humans hastens kidney decline. In humans, that effect is studied most in people with diabetes. In those people, diabetes is destructive to many systems through its effect of raising blood pressure. (ref1, ref2) Yet no one has confirmed that people with CKD who are on a low-salt diet live any longer. (ref)

Many of the commercial dog and cat "kidney health" diets advertise that they are low in salt. But I know of no studies that have shown that low salt diets are beneficial to cats or dogs with kidney disease. Indeed, they all showed that it really did not matter if these diets contained the standard dog and cat nutritional guidelines for salt or had reduced salt levels. (ref1, ref2, ref3, rptref4, ref5, ref6)  One was a bit more equivocal. (ref)

Available low salt kidney care formulas are based more on public perception of the value of low-salt diets in us humans (everyone knows someone on a low salt diet) than on any science that suggests low-salt formulas are of any benefit to dogs and cats with CKD. Salt is a necessary dietary ingredient. If you choose to formulate home-prepared diet for your pet, please keep that in mind.

Is The Omega-3 Fatty Acid Content Of My Pet’s Diet Important ?        PUFAs

Probably so.

There are two groups of omega fatty acids, Omega-3 and Omega-6. The two of most interest in the Omega-3 group, EPA and DHA, are particularly plentiful in oily fish  and krill. Omega-6 fatty acids are particularly plentiful in vegetable oils. A preponderance (more) of Omega 6 fatty acids over Omega 3 fatty acid seems to favor inflammation throughout the body.  Several studies in humans suggest that increasing the intake of Omega-3 Fatty acids might slow the progress of CKD. (ref1, ref2)  What a proper  ratio of Omega-3 to Omega-6 in might be is still a matter of debated. (ref) Others disagree as to the benefits of Omega-3 in slowing the progress of CKD. (ref)

EPA and DHA are not part of the normal diet of land-dwelling carnivores. They get most of their n-3 (omega-3) and n-6 (omega-6) PUFAs in the form of linoleic and alpha-linolenic acid from animal fat – a small amount more from the meat. 

But that does not mean that EPA and DHA might not be helpful to your pet at certain points in its life. Based on the positive human studies, and the fact that the lower-protein diets used in the Minnesota veterinary school studies were also richer in EPA and DHA omega-3 fatty acids, many veterinary nutritionists suggest that adding larger amounts of these Omega-3 PUFAs than are normally found in supermarket brand pet foods might help slow the progress of CKD. (rptref1, ref2)  I tend to agree. Besides, there is little or no downside to giving them to your pet in moderation. Any substance that is active within the body has an effective dose and an excessive dose. If you supplement your pet’s diet with omega-3 fatty acids, give it to them in moderation. Also, you can never be certain of the quality or rancidity of fish oils. When I buy supplements for my pets, I buy those that are intended for human consumption, purchased from vendors that turn their stock over rapidly. 

Is The Fiber Content Of My Pet's Diet Important ?

Added dietary fiber might also be helpful for pets with CKD.

When soluble and insoluble fiber reaches the large intestine, it promotes the growth of bacteria. Some of those bacteria can utilize the same waste products (eg urea) that kidneys normally remove as their food source. Those wastes come in intimate contact with those bacteria through intestinal circulation. That gives some of these wastes an alternative way to leave the body - in the stool. (ref1, ref2, rptref3)

There are also charcoal-derived products that are added to the diets of humans with CKD in an attempt to sop up uremic toxins. I do not know of them having been used in dogs and cats with CKD. (ref

Adding To The  Acid-Buffering Capacity Of Your Pet’s Diet

Many natural metabolic processes generate acidity. It’s the job of your pet’s kidneys to keep body acidity (pH) under tight control. It does so by conserving and creating bicarbonate, a buffer, when blood pH becomes too low (acidosis). In pets with advanced CKD, the kidneys often loose their ability to control acidity effectively. 

In pets as in humans, what we eat influences the amount of acidity we produce. (ref)  The digestion of dietary protein is a major source of that acid and studies have found that lowering protein intake in humans, laboratory animals and dogs decreases the amount of this acid their bodies must deal with. (rptref1, ref2, rptref3)

Some of the commercial "kidney friendly" diets are formulated with added potassium citrate to reduce the acid load on your pet’s body. In addition to providing fiber, fruits and vegetables are also helpful in reducing acidity (metabolic acidosis). (ref)

Might Extra Vitamins Be Helpful ?

Many believe they are – particularly in the later stages of CKD.

First, dogs and cats with reduced appetites are less likely to meet their total vitamin needs.  But second, the increased drinking and urination seen in pets with CKD mean more of the water soluble vitamins - B vitamins and vitamin C - are flush out (lost) through the urine. Older cats in particular seem prone to developing vitamin B-12 deficiencies. (ref)

There might also be some connection between low B vitamin intake and elevated SDMA – although not necessarily involving the kidneys. (ref)

What About Antioxidants ?

Oxidative damage to cells (oxidative stress) and chronic inflammation go hand in hand and both are thought to play a part in CKD. During normal metabolism, compounds containing oxygen are formed that are highly unstable. They long to combine with (oxidize) components of the cells that surround them. (ref) In the process, those cells can be damaged. The body produces its own antioxidants to mitigate that. An important one is glutathione.

Vitamins, like vitamin E (tocopherols), vitamin C (ascorbic acid) and beta-carotene - a precursor of vitamin A, are also antioxidants. Unlike us humans, dogs and cats can synthesize their own vitamin C in their livers. Fat and organ meat are their natural source of vitamin E and eating liver supplies them with pre-formed vitamin A. Traditionally, vitamin E and vitamin C have been added to pet foods as a preservative to control fat content rancidity, extend shelf life and limit ingredient spoilage.

In 2006, Hills Prescription diets ran a study in cats that suggested that a diet enriched with vitamins E, C and beta-carotene antioxidants might protect a pet’s kidneys from oxidative damage. They tested certain white blood cells, lymphocytes, and reported that evidence of DNA damage in those cells was lower in the cats that received the vitamin supplement than in those that didn’t. They also reported that BUN values went down in the cats receiving the supplemented diet. (ref)  Based on that report, a lot of folks (all  associated in one way or the other with Hills or quoting the 2006 Hill’s-sponsored article) recommended that pets with CKD receive extra E, C and beta-carotene. (rptref1, ref2, ref3 ) However, a similar study was performed again with vitamin E in 2016 by different investigators – this time without Hill’s funding. In that study, vitamin E did not affect their measurements of oxidative stress in cats with CKD. Vitamin E also caused no improvement in the degree of anemia these cats experienced. (ref)

Similar ambiguities (?s) occur in interpreting the benefits of dietary antioxidants in people with CKD. In a 2014 study, vitamin E and another antioxidant were given to patients with advanced (stage 4) kidney disease. No effects could be found on the marker tests for inflammation in those people, no improvement in anemia occurred and the patients died at the same rate as those not taking the antioxidants. (ref)  An earlier, 2011 test in patients with less advanced CKD yielded the same negative results. (ref) Another human study with 19,461 participants did find that people who consumed more antioxidant-containing foods in their diet had a bit lower chance of developing CKD. But once a participant on a high or low antioxidant diet had developed CKD, their antioxidant consumption did not influence the rate at which CKD progressed. (ref)

So like the value of omega-3 fatty acids and salt restriction in slowing the progress of CKD in your pet, the actual value of added antioxidants is slippery fish - hard to get a grip on. Everyone, including me, are rooting for antioxidants and omega-3s to give your pet some benefit. When a research study comes up with negative or no positive results one can always rightly argue that the dose was wrong, the mixture was wrong, too much or not enough was given, it was the wrong stage of the disease or the wrong pets were selected for the trial, etc.

So with so few proven ways for veterinarians to slow the progress of kidney failure in your cat or dog and so little down side to adding them, there is certainly no harm in seeing to it that they are components of your pet’s diet - in moderate amounts. I would if it was my pet.

L-arginine

The amino acid l-arginine, is intimately tied to inflammation. In some situations, it produces NO (nitric oxide) which combats inflammation. In other situations, it produces SDMA and ADMA, which have the opposite effect. Because some forms of kidney damage are thought to be inflammation-driven, there has been interest in determining if added l-arginine in the diet has positive effects in CKD. (ref1, ref2, ref3, ref4, ref5)

L-arginine is found in large amounts in meat. The highest level I know of is in turkey. An alternative source of an l-arginine precursor is the juice of watermelons. That too boosts arginine level in diabetes-prone laboratory animals. (ref) Not all finding on the effects of l-arginine supplementation in kidney disease were positive.
(ref)

I do not know of anyone that has examined the effects of arginine supplementation on the markers of kidney disease in dogs or cats. But If you have experience using it, please do let me know.

Appetite Stimulants

Dogs and cats are preprogrammed to have an affinity for the taste of meat. (ref) Picky eating and poor appetite is accentuated during times of stress and disease - and kidney disease is no exception. Sometimes, a little love and coaxing is all that is required. Sometimes warming the food helps. In others, an aromatic tasty gravy topping does the trick. There are many approaches that do not require medication. (ref)

But there will come a point where those techniques will no longer work. In those situations, many vets find mirtazapine (Remeron®) an effective way to keep the pets eating. Mirtazapine is an antidepressant; but it has appetite-stimulating effects as well. (ref)

Newer to the market is Entyce (capromorelin). (ref1, ref2, ref3 , ref4) The medication seems quite effective with few, if any side effects. There was actually one study that appeared to show that treatment with ghrelin, a compound with similar effects to capromorelin, seemed to be helpful in retarding inflammation in experimental models of kidney failure. (ref)

I spoke to some of the authors of these studies and asked if Entyce might be useful in combating the poor appetite of pets with CKD. This was their reply.

If you gain experience using Entyce in your pet with CKD, I would appreciate your letting me and other readers know the results. I will post those comments here.

Ketoacids

The ten essential amino acids for dogs and cats include arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Cats have an additional requirement for the essential amino acid taurine. (ref) Meat protein supplies all of them to your pets. Commercial “kidney health” diets make sure enough of those amino acids are present in their lower-protein diets by using better quality animal and vegetable protein sources.

In the later stages of human kidney disease, when some physicians believe that truly low protein diets are advisable, some physicians and nutritionists  attempt to get around the dangers of low protein by supplementing the patient’s diet with amino acids that have been enzymatically oxidized into keto (C=O) amino acids. (ref) In many European and Asian locations, where kidney dialysis and kidney transplants are less available, low protein diets, supplemented with ketoacids, are considered an accepted way to maintain CKD patients and perhaps slow the progress of their kidney failure. (ref1, ref2, ref3)

The ketoacids products generally used there are Ketosteril® or AlfaKappa®. To the best of my knowledge, neither are sold in North America. I know of no one who has tried them in dogs or cats to keep down blood toxin levels when low to moderate protein diets are given to pets with CKD.Let me know. if you do.

If I Decide To Put My Cat or Dog On A Prepared Kidney Diet Do You Have A Favorite Brand ?

I believe that the major brands, Hills, Purina and Royal Canin, follow similar enough formulas in their renal diets to produce similar results. There are other smaller companies. They hopefully manufacture diets similar to the larger companies themselves or have contract packers make it for them. (ref1, ref2) I cannot speak for their quality. I cannot tell you if their ingredients are standardized or analyzed from batch to batch or where they are obtained. I cannot tell you if they used the services of certified veterinary nutritionist. I can not tell you if they test-feed there products to cats and dogs.

Acceptable taste to your pet is another matter. Ask your veterinarian if he/she would provide small samples of different brands for your pet to check out. 

My personal preference is Royal Canin. That is not because I know that their products are any more effective than the others. It is because of my respect for the Waltham Pet Nutrition Center and their pioneering work on kidney diets. (ref1, ref2)   It is also because I believe that they make fewer unsubstantiated claims for their diets. I have always found the studies Waltham generates on nutrition more credible - both those produced internally (ref)  and those performed with the collaboration of the Royal Veterinary College, UK, another institution dear to my heart. (ref) But unsubstantiated crowd-pleasing claims, studies that were poorly designed and selling points purloined from the popular press do not impress me very much. (ref)

No matter what diet you choose, I suggest you consider its moisture content. You know from my other articles how important I believe that proper hydration is in the prevention of CKD in cats and dogs. I encourage you to purchases either the canned forms of these diets or plan to gradually increase the water content of their dry products. Total daily water intake is considerably greater in cats when they eat canned or moist diets – no matter how many water bowls you set in front of them. (ref1, ref2) I believe it is beneficial to dogs too. I know that adding water or broth to dry diets is messy and inconvenient for you; but I believe that it is important. Remember that canned products have add jelling agents for owner eye-appeal. So they look to you like they have less water than they actually do. Most dry foods are 8-10% water. Most canned foods, about 70-80% water. Most natural prey 60-70% water. You can do the math to see how much to add. That advice goes for your pets even if you elect to keep them on an over-the-counter senior food like Royal Canin/Mars’ Royal Canin Senior Consultant which is really not that different from Royal Canin Feline Renal Support prescription diet – particularly if you add a moderate amount of poultry fat. Similar strategies with closely comparable diets can be used when your pet is

a dog. (ref)

Does My Pet Still Need To Be Monitored While On A Kidney Diet ?

Yes.

Even if they are not required now, there will be a time when medications are needed. If they are required now, there will be a time when their doses need to be adjusted.

Veterinarians use the tests I mention in my kidney treatment article and elsewhere on my website (creatinine, urine protein:creatinine ratio) consecutively to monitor your pets real-time kidney health.  Even those values can vary ~30% from day to day. In dogs that are eating less protein, those values often go down irrespective of kidney health improvement.  (ref1, reptref2, rptref3, rptref4)  

The most important thing you can do at home is purchase an accurate scale and keep a weight diary. A stead body weight, or increased weight in thin pets along with a normal serum albumin protein level suggest that the diet is meeting your pet’s nutritional needs. (ref1, rptref2)

Some pet owners are not that good at judging their pet’s body weight score or telling when their pet is thin, lean, fat or just right. BCS= body condition diagrams, as in this article, can help with that : (ref)
 
Just because these "kidney health" diets meet the nutritional needs of one pet doesn’t necessarily mean it will meet the nutritional needs of another. (ref1, ref2

I suppose this is as good a place as any to remind you to avoid over-vaccinating your pets. There is some evidence it could even have negative effects on their kidneys. (ref1, ref2

Can I Prepare A More “Kidney-Friendly” Diet At Home ?

Click on Mr. Van Patten to learn more about why you might want to do that.

I mentioned earlier that one might take a senior dog or cat diet, reduce its protein content with added fat and fortify its vitamin and omego-3 content to produce something quite similar to the commercially available products. If that is done in moderation, some might attempt to do that alone. But forging your own path is not without risk. It would be assuring to me to have the helping hand of an experienced animal nutritionist.  Many veterinary schools have a board certified nutritionist (ACVN-Certified) on staff who will do that. Many commercial services, staffed by certified animal nutritionists, will assist you with that as well.

There are other folks who derive comfort in knowing that the quality of the ingredients they feed their pet are the same quality as the ingredients of the food they eat. Sometimes, they are not. (ref)

The optimal kidney diet for dogs and cats is not yet known. It is unlikely that it is the same as one we humans need (and even what is best for us is debatable) but reading how human nutritionists approach diets for  CKD might be of interest to you. (ref1, ref2, ref3)

I mentioned earlier that the phosphorus in plant proteins was less available than the phosphorus in meat. But even meats differ in their phosphorus content. A good starting point to learn about that are the tables of the ASIA PACIFIC JOURNAL OF CLINICAL  NUTRITION. (ref) If that link won't open, try this doc.


Some protein-to-phosphorus differences between food sources may not be readily apparent. For instance, egg yolks have 16 times as much phosphorus per gram of protein as do egg whites. (ref)