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Requirements
Overview
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This section contains information on the nutritional
requirements of CKD cats, and includes a discussion of the low protein
debate.
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It also discusses other nutritional issues, such as
whether to free feed, and the relative merits of dry and canned food.
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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
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Cats are not small dogs. They have unique physiological
needs. When you are dealing with CKD, you need to meet these basic needs but
also cater as far as possible for their CKD-related needs.
Basic
Physiological Needs
There are many different opinions
about the best food for cats, and the debate can get quite heated. I don't
wish to focus on that here, but rather to explain the basic needs of cats
from a scientific perspective.
Cats are obligate carnivores.
This does not mean they can only eat meat. It means that, unlike other
species, such as humans and dogs, they cannot themselves manufacture certain amino
acids essential to life. In order to obtain these amino acids, they must eat
food which contains them, and ideally that means they must eat
meat, though they may also be able to obtain them from other sources (corn
gluten meal, the protein part of corn, actually contains all the amino acids
which cats need).
It is a myth that our domestic cats are miniature
versions of the big cats such as lions. Big cats are part of a pride, and
hunt together. Domestic cats, in contrast, are solitary predators, and if
they are living in their own version of the wild, they only
eat what they can catch. They catch mice, insects, whatever passes by or
what they can hunt. This means they have evolved to eat little and often.
They eat very little plant material or carbohydrate, only what would be
found in a mouse's stomach, though they may sometimes also eat small amounts
of grass.
Originally cats were desert animals, so they evolved not
to want to drink much. Since a mouse is approximately 60% water, historically
this was not an issue - they got sufficient fluid intake from their food.
Therefore ideally cats also need to eat foods containing a reasonable amount of
water.
Geometric analysis of macronutrient selection in the
adult domestic cat, Felis catus
(2011) Hewson-Hughes AK, Hewson-Hughes VL, Miller AT, Hall
SR, Simpson SJ & Raubenheimer D Journal of Experimental Biology
214 pp1039-1051 found that "the intake target lies close to 26g day
protein, 9g day fat and 8g day carbohydrate, yielding a macronutrient energy
composition of 52% protein, 36% fat and 12% carbohydrate."
So to summarise, healthy cats need foods containing a
large percentage of meat-based protein, with limited vegetables and grains.
They need to eat little and often, and ideally a wet food containing around
60% moisture; but the
ingredients are more important.
The feeding behavior of the cat (2010) Horwitz D, Soulard Y & Junien-Castagna A Encyclopaedia of Feline
Nutrition pp439-477 is an excellent overview of feline eating
habits.
Physiological Needs of CKD Cats
It becomes a little more complicated when you add CKD
to the mix. You still want to feed a diet that meets your cat's basic
physiological needs, as outlined above, but if possible you also want to
feed a diet that can help with
the CKD.
There are two main concerns with diet in CKD cats.
Firstly, ideally you do not want to feed anything that may make the disease progress
faster and/or make the cat feel poorly. Secondly, you want to keep your cat
eating and keep weight and muscle on.
Below I discuss the components of diet, such as protein
and phosphorus, and also how some of the other issues relating to feline
needs (such as free feeding) tie in with CKD. The protein section includes
information about the pros and cons of a low protein diet.
I recommend that you read this page so you
can understand the main components of feline diets, and why prescription
renal diets differ from normal diets. Then you can read about
Which Foods to
feed, which discusses the introduction of prescription diets and what to do
if your cat refuses to eat them. Remember, the most important thing is that your cat eats.
I cannot emphasise this enough. If you're struggling to get any food at all into
your cat, check the
Persuading Your Cat to Eat page.
Calorie Needs
and Weight Issues
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Weight and Body
Condition
You should monitor
your cat's weight and body condition closely. Weight loss is one
of the major headaches of CKD. It happens partly because many CKD cats have
poor appetites, and partly because older cats have a natural tendency to lose
weight, particularly in the form of muscle mass. However, CKD cats also lose weight because of the disease.
Mechanisms causing loss of lean body mass in kidney disease
(1999) Mitch WE The American Journal of Clinical Nutrition 67
pp359-66 explains more about this problem in humans.
Anorexic cats (who have stopped eating) and cachexic
cats (cats who have lost a lot of
muscle) have a worse prognosis than cats of a normal weight, so it is
essential to monitor weight and calorie intake, and above all to keep your cat
eating.
Purina has a Body Condition diagram
showing how to gauge your cat's physical condition. In
Staged management of chronic kidney disease in dogs
and cats (2009) Presentation to the World Small
Animal Veterinary Association World Congress, Dr D Polzin says: "Ideally patients
should consume sufficient
calories from an appropriate diet to maintain a body condition score of 4 to
5/9. Increased efforts are
indicated to assure sufficient calorie intake for patients with body
condition scores of 3/9 or lower or
when patients fail to consume adequate calories to maintain a stable,
appropriate body weight."
If you are lucky
enough to have an overweight CKD cat, rejoice, and certainly don't put him or
her on a diet, because as the CKD progresses, your cat will almost certainly
lose weight anyway.
Calorie Needs
When considering a food, you not only need to consider
phosphorus and protein levels (see the
Food Data Tables
for information on phosphorus and protein levels in a variety of commercial
foods), but
you also need to consider the calorie content. Most canned foods contain
around 80% water, but some are as much as 85% water. Whilst increased fluid
content can be helpful for CKD cats, who are at risk of dehydration, the
downside is that such foods may make the cat feel relatively full while
providing insufficient calories for the cat's needs (see
below). This is often the case
with simple foods that consist largely of meat or fish. Lower fat foods may
also contain fewer calories.
Some manufacturers provide data about
the metabolisable energy (ME) of their foods.
Metabolizable energy: a way to looks at caloric
density by Dr Holly Nash explains
how foods vary in terms of the number of calories which are actually
available to a cat after digestion: "Pet foods with higher ME numbers
provide your pet's body with more concentrated calories for more energy.
With a higher ME, your pet's body will receive more energy from a smaller
amount of food." This can be helpful for CKD cats who tend not to have much
appetite.
I am often asked if I could add calorie details to the
food data tables. I do plan to do this, but in the meantime you can check
the food you are considering feeding for the ME levels, or find the
calorie content of some US foods
here (canned)
and
here (dry).
Stanley Marks discusses feline
dietary and calorie needs in
Diagnostic and therapeutic approach to the anorectic cat (2001),
Presentation to the World Small Animal Veterinary
Association World Congress 2001.
Petdiets can help you work out how much
food your cat needs each day.
Food Composition and Requirements
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The usual guidelines for CKD cats are to feed a
diet which has added potassium but which is low in protein, phosphorus and
sodium. It is helpful to understand the reasoning
behind these recommendations.
Protein
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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 mean), and therefore cats must ideally eat meat in order to obtain
these amino acids. This is why cats are known as obligate carnivores. When
people feed a cat a vegetarian diet (which I definitely do not recommend
for any cat), they provide these amino acids in the
form of supplements, but cats are optimally designed to obtain them from meat.
Feline Protein Requirements
Nutrient Requirements of Cats
states that healthy cats need an absolute minimum of 3.97g of protein per kg of
cat, or 1.8g per lb of cat, so a 4.5kg or 10lb cat would need a minimum of
18g of protein a day.
Geometric analysis of macronutrient selection in the
adult domestic cat, Felis catus
(2011) Hewson-Hughes AK, Hewson-Hughes VL, Miller AT, Hall
SR, Simpson SJ & Raubenheimer D Journal of Experimental Biology
214 pp1039-1051 found that in fact for the average cat, "the intake target lies close to 26g day
protein..., yielding a macronutrient energy
composition of 52% protein." Dr D Zoran believes that healthy cats should eat
a diet containing around 45% protein on a
dry matter analysis (DMA) basis.
This level of intake may not be sufficient for older
cats. In
Feeding old cats - an update in new nutritional
therapies (2011) Sparkes A Topics
in Companion Animal Medicine 26(1) pp37-42, Dr Sparkes states
that older cats need more calories than younger cats, preferably in the form
of protein. He adds that older cats also seem to do better when fed a diet
containing
prebiotics, antioxidants and essential fatty
acids.
As far as CKD cats are concerned, in
Slowing the progression of chronic renal failure
(2004), Dr DF Grauer states that the minimum protein requirements of cats with
CKD are actually higher than those of healthy cats. However, he recommends that
cats should receive "a minimum of 3.3 to 3.5 g of protein per kilogram
body weight per day", which is actually less than recommended for
healthy cats in Nutrient
Requirements of Cats above. He also states "At the same time, the patient’s
serum
creatinine and
albumin concentrations as well as their body weight
should be stable."
Ohio State University states that protein
should never be reduced to less than 20% of calories for CKD cats (scroll down to the
slides labelled Conservative Medical Management of CRF: Protein
Restriction?).
What is
High Quality Protein?
During the breakdown of dietary protein in the digestive process,
waste substances are created which are filtered out of
the blood by the kidneys and excreted via
urination. This is sometimes referred to as the removal of
nitrogenous wastes.
Unfortunately damaged kidneys find
it harder to do this, which is why
BUN levels rise in CKD.
Thus the goal in CKD is to feed
a protein with the correct balance of amino acids to provide the cat with
the ability to maintain and repair bodily tissues, but in a form which needs
as little breaking down as possible. That is what we mean in this context by
"high quality protein." In other words, if you feed a human grade cat food
that contains expensive organic chicken breast, you may not necessarily be
providing high quality protein in the form that is required for a CKD cat.
Pet Education has an overview of protein
requirements in cats.
Why Vets Recommend Low Protein
The reasoning behind this recommendation is that feeding
a low protein diet reduces the amount of nitrogenous wastes that must be
processed by the kidneys. This usually leads to a reduction in
BUN
levels and in turn the cat will often feel and act better.
Nutritional management of feline chronic kidney
disease (2008) Elliott J, Elliott D
Veterinary Focus 18(2) pp39-44 states that this is "most
appropriate for late Stage 3 and Stage 4 CKD cats."
This paper also states that protein restriction may
"decrease
proteinuria mediated by glomerular hyperfiltration, a mal-adaptive
response to CKD which contributes to progressive renal injury. This is the
reason for reducing protein intake in Stages 2 and 3 of CKD." However, the
authors themselves admit that "The efficacy of reducing protein intake as a
treatment for proteinuria is highly controversial in the cat and dog."
It must be remembered that when vets recommend
prescription renal diets, they are not only recommending low protein.
Prescription kidney diets have other attributes, for example lower protein
diets also tend to contain less phosphorus, and phosphorus control is
extremely important in CKD cats (see
below). You can read more
about the attributes of prescription kidney diets on the
Which
Foods to Feed page.
The Low
Protein Debate
There is a lot of controversy about how useful
low protein diets are for CKD cats, and when they should be introduced. Part of the
controversy arises from the fact that many of the older studies which advocate the feeding
of lower protein diets to CKD patients were performed on humans and rats,
and therefore their findings may not be appropriate for cats, with their uniquely complex
nutritional needs.
There are some
studies into the use of low protein diets in CKD cats. In
Effects of dietary protein and calorie restriction in
clinically normal cats and in cats with surgically induced chronic renal
failure (1993) Adams LG Polzin DJ Osborne CA & O'Brien TD American Journal of Veterinary Research 54
pp1653-1662, CKD cats were fed either high (38%) or low (20%) protein diets
for one year. The cats fed a high protein diet had higher
BUN levels
(as might be expected) than the cats fed a low protein diet (who were fed
2.7g/kg per day) but they also
had lower creatinine levels; and they also ate more and gained weight
compared to the cats on the low protein diet, some of whom showed signs of
malnutrition towards the end of the study. Some of the cats fed the high
protein diet did develop transient
hypokalaemia
(low potassium levels), which might have been because the low protein diet
contained more potassium. Please note that the CKD cats in this study did
not have naturally occurring kidney disease.
In
Protein and calorie effects on progression of induced chronic renal failure
in cats (1998) Finco DR, Brown SA, Brown CA, Crowell WA, Sunvold G & Cooper TL American Journal of Veterinary Research 59
pp575-582, cats were divided into four groups: low protein, low calorie
(A); low protein, high calorie (B); high protein, low calorie (C); and high
calorie, high protein (D). No real differences were seen after a year, and
there was no change in
GFR in any group.
A vet from Ohio State University College of
Veterinary Medicine stated
with regard to this study: "recent findings in cats with
induced renal insufficiency suggest that feeding diets restricted in protein
may not be necessary for this species. Cats fed 9g of protein per kg
of bodyweight per day had no more severe kidney lesions or lower GFR than
did cats fed 5.2g of protein per kg of bodyweight per day". In
Effects of dietary protein intake on renal function (1999) Supplement to
Compendium on Continuing Education for the Practising Veterinarian 21
Dr Finco stated "the negative results from the
second study indicate that protein restriction in cats with renal disease
remains to be proven as an effective maneuver for ameliorating progression
of renal disease".
There are also
some studies into the use of
prescription kidney diets, which of course are
not only low protein. In
Survival of cats with naturally occurring chronic renal failure: effect of
dietary management
(2000) Elliott J, Rawlings JM, Markwell PJ, Barber PJ
Journal of Small Animal Practice 41 pp235-42, 29 cats were
fed a low protein, low phosphorus prescription diet, while a further 21 cats
did not eat the prescription diet. Some of the cats (presumably in both
groups) were also given phosphorus binders. The cats fed the prescription diet
survived longer than the other cats, but it is not clear whether this was
due to the reduction in phosphorus intake rather than the reduction in
protein intake. The study concluded "Feeding a veterinary clinical diet (with intestinal
phosphate binders where necessary) specifically formulated for feline renal
failure was associated with a highly significant beneficial effect on
survival of cats presenting with naturally occurring stable CKD. This is the
first prospective dietary study involving naturally occurring feline CKD
cases where survival from first diagnosis has been assessed."
Nutritional management of feline chronic kidney
disease (2008) Elliott J, Elliott D
Veterinary Focus 18(2) pp39-44 states that "protein
restriction may "decrease
proteinuria mediated by glomerular hyperfiltration, a mal-adaptive
response to CKD which contributes to progressive renal injury. This is the
reason for reducing protein intake in Stages 2 and 3 of CKD." However, the
authors themselves admit that "The efficacy of reducing protein intake as a
treatment for proteinuria is highly controversial in the cat and dog",
adding that this may lead to malnutrition.
The study that
most experts cite when recommending a prescription kidney diet is
Clinical evaluation of dietary modification for
treatment of spontaneous chronic kidney disease in cats
(2006)
Ross SJ,
Osborne CA,
Kirk CA,
Lowry SR,
Koehler LA,
Polzin DJ Journal of the American
Veterinary Medical Association 229(6) pp949-57. This study found that feeding a
prescription kidney diet helped to keep
BUN levels lower and appeared to help prevent
metabolic
acidosis in cats with more advanced CKD. The study concluded "The renal diet evaluated in this study
[Hill's k/d]
was superior to an adult maintenance diet in minimizing uremic episodes and
renal-related deaths in cats with spontaneous stage 2 or 3 CKD." By Stages 2
and 3, they are referring to cats with creatinine between 2.1 and 4.5 mg/dl.
The
Downsides of Low Protein
One problem with
lowering protein intake in cats is that it may have unintended side effects.
In
Slowing the progression of chronic renal failure
(2004) Dr GF Grauer states that "There are, however, potential undesirable
effects associated with dietary protein reduction. Specifically, if dietary
protein is restricted in relation to the animal’s protein needs, reduced
renal hemodynamics, protein depletion (decreased body weight, muscle mass,
and serum albumin concentration), anemia, and acidosis can occur or be
aggravated."
Low protein diets
are also of concern for cats with metabolic acidosis, because, according to
Nutrition and renal function in cats and dogs: acid-base, electrolytes and
renal failure (1999) Polzin DJ, Osbourne
CA, James K Supplement to Compendium on
Continuing Education for the Practising Veterinarian 21 11(K),
studies of rats and humans with renal failure show that "acidosis may limit
the ability of patients to adapt to dietary protein restrictions." It is not yet certain whether acidosis also affects cats in this
way, but it seems plausible, given the cat's
relatively high requirement for protein.
Should I
Feed Low Protein?
IRIS Stages
1 and 2
Because of the
potential downsides of protein restriction, it is not necessarily a good
idea to feed low protein food in all cases. For cats in Stage 1 or early
Stage 2 of CKD under the IRIS system (creatinine between 1.6 and 2.8 mg/dl,
or 140 and 250 mmol/L), the risks of low protein food may outweigh the
benefits, and therefore many vets do not advocate protein restriction in
these stages. In
Managing chronic diseases in cats
(2005) Veterinary Medicine Dr S Little states
"Don't restrict dietary protein for cats
experiencing mild to moderate chronic renal insufficiency (creatinine 1.6 to
2.8 mg/dl, 140 to 250 μmol/l) because it can lead to protein malnutrition.
These cats require adequate protein and calories to maintain body weight and
to avoid muscle wasting and anemia."
If your cat also
has hyperthyroidism, it can be even more of a concern since hyperthyroid
cats are prone to weight loss and muscle wasting.
In
Diet and nutritional management for hyperthyroid cats
(2011) Dr ME Peterson states that for cats with
both CKD and hyperthyroidism, reducing protein should be
avoided for cats in IRIS stages 1 and 2, but that phosphorus control is
very important.
If you decide not
to feed low protein, please do ensure that your cat has a low phosphorus
intake.
IRIS Stages
3 and 4
Since
BUN
is influenced by protein intake, it does often help the cat feel better
if you restrict protein intake as the CKD progresses. Generally speaking,
once BUN levels are over 60, you are more likely to see symptoms such as
vomiting and nausea, so this is a point at which
many vets recommend that you start restricting
protein intake. In
Slowing the progression of chronic renal failure
(2004) Dr GF Grauer states that "As the renal failure progresses, additional dietary
protein reduction will likely be necessary. Dietary protein reduction
should be initiated when the animal’s blood urea nitrogen concentration is
between 60 and 80 mg/dl."
The usual goal is around 25% protein on a dry matter
analysis (DMA) basis. For most people, the easiest way to achieve
this is to feed a renal prescription diet: these diets have a protein level
of around 25-30%. You can also check the
Food Data Tables to find other foods
which are relatively low in protein, but don't forget the prescription diets
do not only consist of low protein, and the protein they do contain is good
quality from the CKD perspective.
Unfortunately, it
can often be easier to switch a cat to a low protein diet when the cat is
stable with lower numbers. So if your early stage cat is prepared to eat a
low protein renal diet, it is worth feeding. The manufacturers claim that
their diets have adequate protein levels for cats at every stage of CKD, but
if you are concerned,
consider adding foods with high biologic value but minimal nitrogenous
waste. A good choice would be
eggs.
If your cat has
been diagnosed with CKD and has BUN over 60 (urea over 21), you may panic if
you cannot get your cat to eat a low protein food. Take a deep breath.
In
Managing chronic diseases in cats
(2005) Veterinary Medicine Dr S Little states "Never try to
force an anorexic patient with chronic renal insufficiency to eat a
protein-restricted diet. Instead, concentrate on encouraging anorexic
patients to eat." Focus on getting food into your cat and getting him or her
stabilised before you worry about feeding low protein. See the
Which Foods to Feed
page for more tips on getting your cat to eat the prescription diet and what
to do if you can't succeed. See the
Persuading Your Cat
To Eat page for tips on getting your cat to eat. See below for
information on Astro's Protein
Powder. Whatever you do, monitor your cat's weight
closely.
Phosphorus
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In contrast to the protein debate, there is no
dispute about the importance of controlling phosphorus levels for CKD cats.
High phosphorus levels are very damaging to their health and can make the
disease progress more quickly.
This is such an important topic that I have
an entire page devoted to
phosphorus control. Please read it and do everything you can to keep your cat's
phosphorus levels low - it can make all the difference to your cat's health
and prolong survival.
Fat
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Just as cats need a diet relatively high in
protein, so they also need relatively high levels of fat compared to a human
or dog. Geometric
analysis of macronutrient selection in the adult domestic cat,
Felis catus
(2011) Hewson-Hughes AK, Hewson-Hughes VL, Miller AT, Hall
SR, Simpson SJ & Raubenheimer D Journal of Experimental Biology
214 pp1039-1051 found that the fat target for healthy cats is about 9g a day
or 36%.
Fat does not result in a lot of waste products like protein,
so processing it is not a strain on the kidneys; plus cholesterol is not an
issue for cats the way it is for humans (see
blood chemistry panel). Fat has been implicated in the development of
obesity in healthy cats, but obesity is hardly a problem for the average CKD
cat. Thus, a diet relatively high in fat can help a CKD cat to maintain his/her weight whilst placing less strain on the
kidneys.
In most CKD prescription foods, the fat content
is increased to compensate for the lower protein levels; but many senior cat
foods also have relatively high levels of fat and relatively low levels of
protein; as a bonus, they often also have low phosphorus. Therefore, if your
cat won't eat prescription foods, it is worth considering senior foods.
Sodium
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The kidneys cannot process sodium as effectively
in CKD, which increases the risk of hypertension (high blood pressure) in
humans.
It used to be thought that the same applied to cats, and it was therefore
recommended that sodium intake should be restricted. However, one study,
Effects of dietary sodium chloride intake
on renal function and blood pressure in cats with normal and reduced renal
function
(2004) Buranakarl C, Mathur S & Brown SA
American Journal of Veterinary Research 65(5) pp620-7 found
that "this common dietary maneuver could contribute to hypokalemic
nephropathy and progressive renal injury in cats."
A later study,
Effects of sodium chloride on selected parameters in
cats (2006) Kirk CA, Jewell DE, Lowry SR Veterinary
Therapeutics: Research in Applied Veterinary Medicine 7(4)
pp333-346 found that sodium intake appeared to have no effect on in blood pressure in
CKD cats, but that levels of BUN, creatinine and phosphorus were
higher in the cats eating a high sodium diet compared to those eating a low
sodium diet.
Effects of dietary sodium chloride on health
parameters in mature cats (2009) Xu
H, Laflamme DP & Long GL Journal of Feline Medicine & Surgery 11(6)
pp435-41 examined a low sodium diet (0.55%) and a high sodium diet (1.11%)
fed to mature cats over a period of six months. Even in cats with creatinine
over 1.6mg/dl, "there remained no evidence of adverse effects
associated with increased salt intake. These results are consistent with the
majority of other studies evaluating sodium intake in cats, as well as with
the National Research Council's assessment, all of which indicate that
sodium at 1.5% of the diet dm is not harmful to healthy cats."
Pet food safety: sodium in pet foods
(2008) Chandler ML Topics in Companion Animal Medicine
23(3) pp148-53 states that "there is no strong evidence that increased dietary sodium increases the risk
of hypertension in dogs and cats, and the current recommendation for hypertensive
animals is to avoid high dietary salt intake without making a specific
effort to restrict it... Increased dietary
sodium increases urine output and may decrease the risk of forming calcium
oxalate uroliths due to the decrease in relative supersaturation of solutes.
However, caution should be used in increasing the sodium intake of patients
with renal disease as increased dietary sodium may have a negative effect on
the kidneys independent of any effect on blood pressure."
So should you restrict sodium intake or not?
The International Renal Interest Society
states on page 5 that there is no evidence that reducing sodium
intake is helpful for
CKD cats, and that it should certainly not take the place of medication for
hypertension, but
if you do opt to do this, you should do it gradually. The
food data tables provide information about the sodium content of many
cat foods available in the USA and UK.
Potassium
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Around 30% of CKD cats have
potassium levels which
are too low. This occurs because potassium is easily lost through increased urination and
vomiting. The prescription foods
contain extra potassium (all cat foods need some potassium), and this is
usually in the form of potassium citrate, because potassium citrate may help
with a problem seen in some CKD cats known as
metabolic acidosis.
If your
cat refuses to eat a prescription diet, your vet can give you a potassium supplement
instead, if appropriate; some cats need a potassium supplement whether or
not they eat the prescription food.
Many commercial cat foods
are acidified in order to reduce the risk of
FLUTD
(feline lower urinary tract disease. These foods often say that
they are designed to maintain urinary tract health; or they may contain
cranberries or additional
Vitamin C. However, these foods (which are actually designed to treat a different kind
of problem to CKD) may have the effect of increasing the amounts of
potassium lost in the urine, which is bad for CKD cats. It is therefore best
not to feed acidified foods to CKD cats, who tend to have quite high
acid levels anyway.
Carbohydrates
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Cats only have a limited need for carbohydrates -
a cat catching his/her own food would only eat the small amount of
carbohydrate contained in a mouse's stomach.
Geometric analysis of macronutrient selection in the
adult domestic cat, Felis catus
(2011) Hewson-Hughes AK, Hewson-Hughes VL, Miller AT, Hall
SR, Simpson SJ & Raubenheimer D Journal of Experimental Biology
214 pp1039-1051 found that target intake for carbohydrate in cats was
only 8g a day or 12% of total food intake. It also states "Our analysis indicates that cats have a ceiling for carbohydrate intake,
which limits ingestion and constrains them to deficits in protein and fat
intake (relative to their target) on high-carbohydrate foods."
In
The carnivore connection to nutrition in cats
(2002) Zoran D
Journal of the American Veterinary Medical Association 221
pp1559-67, Dr Zoran writes "It is clear that cats have a greater need than
dogs or other omnivores for protein in their diet. Cats also have several
physiologic adaptations that reflect their expected low CHO [carbohydrate]
intake... These specific differences do not mean cats cannot use starch. In
fact, cats are extremely efficient in their use of simple sugars. However,
it does underscore their development as carnivores and the expected low
amounts of grain in their typical diet. These digestive differences may mean
that high amounts of CHO in diets may have untoward effects on cats."
Therefore, if you are trying to reduce your CKD cat's
protein intake, I would recommend increasing the fat in the diet (see
below) rather than the carbohydrates. If you are
feeding a prescription diet, this will be done automatically - many of
these diets increase the fat content rather than the carbohydrates in order
to offset the reduced protein content.
Pet Education has an interesting article
about carbohydrates in the feline diet.
Fibre
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Fibre is the non-digestible component of
complex carbohydrate. It
is important for good digestive health. It may also assist with two commonly
seen CKD problems, toxin reduction (via nitrogen trapping) and
the control of constipation.
There are two different types, fermentable and non-fermentable.
Which fibres are fermentable depends upon the species.
Fermentability of selected fibrous substrates by cats
(1994) Sunvold GD, Titgemeyer EC, Bourquin LD, Fahey GC & Reinhart GA The
Journal of Nutrition 124 pp2721S-2722S examines the degree of
fermentability of various fibres.
Diet and large intestinal disease in dogs and cats
(1998) JW Simpson The Journal of Nutrition 128
2717S-2722S has a table showing soluble and fermentable fibres.
In terms of general health, you do not necessarily want the most fermentable fibres.
Dietary fiber for cats: in vitro fermentation of selected fiber sources by
cat fecal inoculum and in vivo utilization of diets containing selected
fiber sources and their blends
(1995) Sunvold GD, Fahey GC Jr, Merchen NR, Bourquin LD, Titgemeyer EC,
Bauer LL & Reinhart GA Journal of Animal Science 73(8)
pp2329-39 examined the fermentability of various fibres. It concludes that
the diet "which contained the most fermentable fibers, severely decreased
nutrient digestibility and resulted in poor stool characteristics. Diets
that contain moderately fermentable fiber provide fermentation end products
that may be important in maintaining the health of the gastrointestinal
tract of the cat."
Nitrogen Trapping
There has long been interest in whether other bodily
mechanisms might be useful for relieving the load on damaged CKD kidneys.
Bowel as a substitute in renal failure
(1996) EA Friedman American Journal of Kidney Diseases
28(6) pp943-50 states "Extraction, modification, or recycling of
nitrogenous wastes by the gastrointestinal tract is a potentially low-cost
means of substituting for missing renal function. Multiple approaches to the
bowel as a substitute kidney have been attempted."
A 1999 study
Role of
fermentable carbohydrate supplements with a low-protein diet in the
course of chronic renal failure: experimental bases Younes H, Alphonse
JC, Behr SR, Demigné C, & Rémésy C American Journal of Kidney Disease
33(4) pp633-46 indicated that the use of fermentable fibre may help reduce
BUN levels.
Fermentable carbohydrate supplementation alters
nitrogen excretion in chronic renal failure (2006)
Younes H,
Egret N,
Hadj-Abdelkader M,
Remesy C,
Demigne C,
Gueret C,
Deteix P,
Alphonse JC Journal of Renal Nutrition
16(1) pp67-74, a more recent study into the use of fibre to reduce
BUN levels, suggests that this method appears to have
similar benefits to protein restriction without the drawbacks of protein
restriction.
Prescription kidney diets contain fermentable fibre, because some is always
needed to feed the gut bacteria.
Iams has patented a Nitrogen Trap Fiber System containing beet fibre for use
in their kidney prescription food. Hill's uses both beet fibre and locust
bean gum.
Unfortunately,
Nutritional management of feline chronic kidney
disease (2008) Elliott J, Elliott D
Veterinary Focus 18(2) pp39-44 states "classic uremic toxins, unlike urea nitrogen, are medium sized
molecules, too large to easily pass through
the membrane barrier. It is therefore unlikely
that these toxins may be used by the bacteria to
cater for their nitrogen needs. Conversely, the
beneficial effects of fermentable fibers can help to
regulate the digestive disorders that accompany
CKD."
Some forms of fibre, such as fructooligosaccharides (FOS), may also bind
calcium in the small intestine and lead to an increase in calcium levels in
the body (hypercalcaemia).
This is not good for cats with high calcium levels. Inulin and guar gum may do this, as may slippery elm bark and lactulose, two
treatments commonly used for constipation in CKD cats.
The effects of gum arabic oral treatment on the
metabolic profile of chronic renal failure patients under regular
haemodialysis in Central Sudan (2008) Ali AA, Ali KE, Fadlalla AE
& Khalid KE Natural Product Research 22(1) p12-21 found that patients given gum arabic for
three months had lower BUN, creatinine and phosphorus levels, but calcium
levels increased significantly.
Too much fibre may also prevent your cat from absorbing sufficient nutrients or
calories from his/her food. Fibre
may also affect taurine levels
in some foods.
I would therefore recommend discussing additional fibre with your vet before
adding it, and avoiding
its use in a cat who already has high calcium levels.
You can read more about waste product regulation in the
Treatments section.
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.
Essential Fatty Acids
(EFAs)
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What are Essential Fatty Acids
Essential fatty
acids are polyunsaturated fats (sometimes abbreviated as PUFA). They are essential because the body cannot synthesise them, so they have to
be obtained from food. The two main types of EFAs are Omega-3 and Omega-6.
Commercial diets tend to contain far more Omega-6, partly because Omega-6 EFAs
are cheaper and more stable, but this may create a potentially harmful
imbalance. The correct balance is not yet known, though some believe
it is probably around 5:1 (Omega-6:Omega-3).
Qualitative risk assessment of chronic renal failure
development in healthy, female cats as based on the content of
eicosapentaenoic acid in adipose tissue and that of arachidonic acid in
plasma cholesteryl esters (2005) Plantinga EA, Hovenier R
& Beynen AC Veterinary
Research Communications 29(4) pp281-6 concluded that "the fatty acid
composition of cat foods should be determined and that, if deemed necessary,
the ingredient composition should be altered so that the content of EPA [eicosapentaenoic
acid, an Omega-3 type] is
raised and that of AA [arachidonic acid, an Omega-6 type] is lowered."
Essential fatty acids appear to be helpful with many bodily functions. It
has been known for many years that they have an effect on the skin - the first signs of an imbalance or deficiency are usually
a dry coat, itchy skin or matted fur. Recently it appears that they may have
an important role in controlling inflammation. In one study,
Effect of nutritional interventions on longevity in
senior cats (2007) Cupp CJ, Jean-Philippe C, Kerr WW, Patil AR &
Perez-Camargo G The International Journal of Applied Research in
Veterinary Medicine 5(3), healthy older cats fed a diet containing
antioxidants including additional essential fatty acids lived significantly
longer.
Dietary omega-3 fatty acid
supplementation increases the rate of muscle protein synthesis in older
adults: a randomized controlled trial
(2011)
Smith GI, Atherton P, Reeds DN, Mohammed BS, Rankin D, Rennie MJ,
Mittendorfer B American Journal of Clinical Nutrition 93(2)
pp402-12 investigated the effects of EFAs on loss of muscle mass in healthy
older human adults (sarcopaenia). It concluded "Omega-3 fatty acids stimulate muscle protein synthesis in older adults and
may be useful for the prevention and treatment of sarcopenia."
Essential
Fatty Acids for CKD Cats
Whether to
supplement essential fatty acids in CKD cats is a grey area. Research
in rats and humans appears to indicate that the addition of omega-3 fatty
acids to the diet may delay the progression of CKD. However, in
Nutritional management of renal disease
(2008) Presentation to the World Small Animal
Veterinary Association World Congress, Dr K Sturgess states
that "it is possible that supplementation
of diets with PUFA may increase renal damage associated with lipid
peroxidation (degradation of carbon=carbon double bond by oxidants). The
benefits over risks of increasing PUFA levels in the diets of cats with
CRD have not been established." It goes on to say that the
ratio of Omega 3 to Omega 6 may be crucial.
Nutrition and renal function: effects of dietary
lipids on renal function (1999) Polzin DJ, Osbourne CA, James K,
Purina Research Report, adapted from articles presented at the 1998
Purina Nutrition Forum sees things differently. It states:
"In cats, dietary supplementation with n-3 PUFA had no apparent deleterious
effect on lipid metabolism, immune function, blood pressure, or renal
function. At higher levels of supplementation, renal function was actually
increased in normal cats. These data support the assertion that this dietary
maneuver is safe for normal cats and provides some encouragement for further
consideration for dietary n-3 PUFA supplementation in cats with renal
disease, systemic hypertension, or hypersensitivity reactions."
Retrospective study of the survival of
cats with acquired chronic renal insufficiency offered different
commercial diets
(2005)
Plantinga EA, Everts H, Kastelein AM & Beynen AC Veterinary Record 157(7)
pp185-187 found that cats who ate prescription kidney diets with the highest
amount of EPA survived for 23 months versus an average of 12 months for cats
who ate diets containing lower EPA levels.
Oxidative stress and chronic
kidney disease (2008) Brown SA The Veterinary Clinics of North
America. Small Animal Practice 38(1) pp157-66 concludes that "newer data
indicate that dietary supplementation with specific antioxidants is an
important consideration for limiting renal oxidant stress and progression
of CKD." He mentions PUFA as an antioxidant earlier in the text.
Prescription
renal diets have increased levels of essential fatty acids compared to
normal cat food. Almost everybody I know of who has added essential fatty
acids to their cat's treatment plan has been happy with the results,
reporting an improvement in general wellbeing. Ask your
vet if it is appropriate for your cat.
Types of
Supplement
Since cats as
obligate carnivores benefit from animal-based products, the most appropriate form of
essential fatty acid supplement is fish
oil. Fish oil contains Omega-3 fatty acids in the form of eicosapentaenoic acid
(EPA) and docosahexaenoic acid (DHA). However, oils from the liver, such as cod liver oil, are not suitable
because they contain too much Vitamin A and D.
Feeding the aging heart
(2010) Freeman LM & Rush JE Nestlé Purina Companion Animal
Nutrition Summit 2010 Focus on Gerontology states (page 62) "cod liver oil should not be used to provide omega-3
fatty acids because it contains high levels of vitamins A and D, which can
result in toxicity." Look for an oil pressed from
the flesh only and containing EPA and DHA.
Vegetable-based
oils, such as olive oil or
flax seed (linseed) oil, are also not recommended, because they do not
contain the essential fatty acids which a cat needs.
The University of Connecticut
discusses EFAs added to food and mentions that alpha linolenic acid
should be ignored because it is of limited use to cats.
Dietary fish oil and flaxseed oil
suppress inflammation and immunity in cats
(2011)
Park HJ, Park JS, Hayek MG, Reinhart GA, Chew BP Veterinary Immunology &
Immunopathology 141(3-4) pp301-6 found that "fish
and flaxseed oil can reduce skin inflammatory responses in cats, however,
flaxseed oil appears less immunosuppressive than fish oil."
Feeding the aging heart
(2010) Freeman LM & Rush JE
Nestlé Purina Companion Animal Nutrition Summit 2010 Focus on Gerontology
states "Flaxseed or flaxseed oil also should not be used because its
omega-3 fatty acids cannot be efficiently converted to EPA and DHA in dogs
(and particularly in cats)."
If fish oils are given, extra
Vitamin E is also required in
order to avoid a problem called
steatitis.
Vitamin E requirement of adult cats increases slightly
with high dietary intake of polyunsaturated fatty acids (2002)
Hendriks WH, Wu YB,
Shields RG, Newcomb M, Rutherfurd KJ,
Belay T & Wilson J The Journal
of Nutrition: Supplement: Waltham International Symposium 132
pp1613S-1615S discusses this. Too much vitamin E can be dangerous, so ask
your vet how much to give. Veterinary products often contain Vitamin E in an
appropriate dosage (it may be referred to as tocopherol).
Astro's CRF Oil was created by a
human doctor to treat his own CKD cat, and has been on the market since
January 2007.
The manufacturer
states that the product was tested on an informal basis on 18 CKD cats in
the Montreal area over a period of about eight months.
This product is basically a
combination of essential fatty acids,
Vitamin E
and
CoQ10
(ubiquinon), both antioxidants, but in a concentrated formula. You can read
more about it in the
Treatments section.
Dosage
It can be a bit
tricky working out an appropriate dose of fish oil. There is no definitive
dose, and many of the recommendations relate to a particular amount of EPA (eicosapentaenoic
acid), so you will need to check the product you're considering to see how
much EPA it contains. Many fish oil capsules are 1000mg strength. However,
only around 20% of it tends to be EPA (with around 10% DHA), so a 1000mg
capsule will contain around 200mg of EPA and 100mg of DHA.
One recommended
dose of EPA is 22mg per kg of cat per day, or 10mg per lb of cat per day. So
if your cat weighs 8 lb (3.6kg), you would give a product containing 80mg of
EPA each day.
Another
recommended dosage is 180 EPA and 120 DHA per 10 lbs (4.5kg) of cat. As you
can see, this is more than double the earlier dose.
Generally
speaking, it is probably safe to give your cat one 1000mg fish oil capsule daily.
Do check with your vet first though. Renal prescription diets contain
increased amounts of EFAs, so if your cat is eating such a food, you may not
need additional supplementation, or may need a reduced dose.
Essential fatty
acids are commonly available in either capsule form or in pump bottles. Do
not give the oil directly into your cat's mouth, or s/he may aspirate the
oil. Instead, mix the oil (you can open the capsule) with your cat's food.
You don't have to give the daily dose in one amount, you can divide it
between your cat's meals.
Although most cats like fish, the oils can be a bit strong, and many cats
dislike the smell. Some cats may vomit after eating them. It is therefore
wise to start off very slowly, just using one drop at first which you add to
a smelly food that may disguise the test, and gradually increase the dose
over several days or even weeks, If your cat still hates it, you can decant
the oil into a gelcap, try finding a less smelly product, or discuss with your vet whether to
continue with the supplement. Some members of my support group find krill
oil is more acceptable to their cats.
It takes 2-3 months to see the full effect of essential fatty acid
supplements. If you think they help your cat, you should use them on an
ongoing basis.
Essential fatty
acids can turn rancid quite easily. Keep them in the fridge, and check them
regularly to see if they smell off before using them.
Sources
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.
USA
Pet Education
has a very helpful overview of essential fatty acids, with a comparison of
various brands available in the USA.
Consumer Lab has a summary of its findings
with regard to the quality of EFAs, including the names of some of the US
products which met with its approval.
Environmental Defense Fund
has a table showing which brands remove contaminants from their
products.
Welactin is a veterinary product available
in both softgel capsules and pump bottle. One capsule contains 150mg EPA and
100mg DHA. One pump contains approximately 1.8 ml and provides 140mg of EPA
and 216mg of DHA.
CVS sells Sundown Naturals Fish Oil 1000mg
with total EPA and DHA of 300mg.
Grizzly Salmon Oil is made from wild
Alaskan salmon.
Twinlab makes a krill oil product called
Krill Essentials which some people find their cats tolerate better. This is
also available from other suppliers, such as
Vitacost, among others. The dosage for
krill oil (which is made from crustaceans rather than fish) is 500mg per
day.
UK
Salmopet
is a salmon-based fish oil which is widely available in Europe. I haven't
managed to work out its precise composition, but
Vet UK
mentions that it has an EPA/DHA content of 15-25%, and it also contains
Omega 6 oils (which is not ideal). Your vet may also have a suitable product in stock.
Amino Acids,
Particularly Taurine
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Amino acids are the components of protein. There are 23 amino acids
which cats need, and they can manufacture twelve of these themselves, but the
other eleven must be obtained from food.
Taurine
is one example of an amino acid which cats must obtain from food.
Virginia-Maryland Regional College of Veterinary
Medicine explains more about cats and
amino acids.
Plasma amino acid profiles in cats with naturally
acquired chronic renal failure (1999)
Goldstein RE, Marks SL, Cowgill LD, Kass PH & Rogers QR American Journal of
Veterinary Research 60(1) pp109-13, found that CKD cats in all
stages of the disease had lower levels of amino acids than healthy cats.
However, they concluded "the magnitude of these changes is mild and of
little clinical relevance." This is an older study, and it might eventually
be shown that supplementary amino acids are in fact helpful to CKD cats.
Inflammation contributes to low plasma
amino avid concentrations in patients with chronic kidney disease
(2005)
Suliman ME, Rashid Qureshi A, Stenvinkel P, Pecoits-Filho R, Bárány P,
Heimbürger O, Anderstam B, Rodriguez Ayala E, Divino Filho JC, Alvestrand A
& Lindholm B American Journal of Clinical Nutrition 82(2)
pp342-349 also found that amino acid levels are low in human CKD patients with
inflammation and states that the inflammation may be the cause.
Oral supplement of six selective amino acids arrests
progression of renal failure in uremic patients (2004)
Yatzidis H International Urology and Nephrology 36(4) pp91-8
found that amino acid supplements appeared to help human patients with
glomerulonephritis.
If you feed a commercial diet, it will contain the correct balance of amino
acids for cats. However, if you feed homemade food, it is critical to ensure
that the diet has the correct balance of amino acids.
Some highlights in elucidating the peculiar
nutritional needs of cats (2007) Morris JG & Rogers QR Nestle
Purina 2007 Nutrition Forum Proceedings found that problems related to
amino acid deficiencies occurred after a couple of weeks, but that problems
relating to a lack of arginine occurred within less than a day (arginine
deficiency can be fatal in cats very quickly).
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.
Since taurine is only found in animal-based products, this is one reason why
cats are obligate carnivores - eating the flesh of another animal is the
easiest and best way for a cat to take in an adequate amount of taurine.
However,
Plasma amino acid and whole blood taurine
concentrations in cats eating commercially prepared diets (2009)
Heinze CR, Larsen JA, Kass PH & Fascetti AJ American Journal of Veterinary Research
70 p1374 found that there was little correlation between the amount
of protein in the diet and taurine levels in the cat's blood.
A lack of
sufficient taurine in a cat's diet can cause blindness and a type of heart
disease called dilated cardiomyopathy.
Dietary rice bran decreases plasma and whole-blood
taurine in cats (2002) Stratton-Phelps M, Backus RC, Rogers QR &
Fascetti AJ Journal of Nutrition 132 pp1745S-47S mentions that
studies have shown that "Cats fed canned foods require a higher quantity of taurine than those fed
dry foods to prevent taurine deficiency resulting from alterations in the
bioavailability of taurine attributed to the effects of processing."
Feline nutrition update
(2001) Biourge V Presentation to the World
Small Animal Veterinary Association World Congress states "studies
at Davis found that dry extruded cat foods required about 1 g/kg diet, but
canned foods required up to 2.5 g/kg
If cats eat a higher fat or higher fibre
canned diet, they may also require additional
taurine.
Dietary rice bran decreases plasma and whole-blood
taurine in cats (2002) Stratton-Phelps M, Backus RC, Rogers QR &
Fascetti AJ Journal of Nutrition 132 pp1745S-47S mentions that
"In
addition to processing, both the fiber and fat content of canned feline
diets may affect taurine metabolism through an alteration of intestinal
bacteria and subsequent changes in the excretion of bile acids."
Taurine and inflammation: a new approach
to an old problem
(1997) Letter in the Journal of Leukocyte Biology 61(2)
pp231-2 concludes "we believe that taurine may play a vital role in the
management of
inflammation."
There is plenty
of taurine in all cat foods, with more in prescription renal diets. However,
some people do choose to give taurine supplements to their CKD cats. Taurine is water
soluble, so any excess should be urinated out. However,
Accumulation of taurine in patients with renal
failure (2002) Suliman ME, Bárány
P, Divino Filho JC, Lindholm B & Bergström J Nephrology Dialysis
Transplantation 17(3) found that some human renal patients given
taurine supplements complained of feeling dizzy, and tests showed that their
taurine levels were far in excess of normal following supplementation.
Unlike cats, the human body can produce its own taurine, so this might be a
factor in the side effects seen in this study. I
don't know if there would be a similar risk with cats, but please do not
supplement taurine without your vet's approval.
Vitacost sells
3 oz of Source Naturals taurine powder for US$5.59.
Arginine
One of the other amino acids that cats require is
arginine.
Arginine: an essential amino acid for cats
(1978) Morris JC & Rogers QR The Journal of Nutrition 108
pp1944-53 explains more about arginine. Arginine is important for insulin
production in cats, and is also necessary to convert ammonia into urea, a
role so important that a cat fed a diet deficient in arginine
will develop high ammonia levels and may die.
Some highlights in elucidating the peculiar
nutritional needs of cats (2007) Morris JG & Rogers QR
Nestle Purina 2007 Nutrition Forum Proceedings explains that severe
problems relating to a lack of arginine occurred within less than a day,
with one cat dying.
Arginine is also used to make nitrous oxide in the
kidneys. It is thought that nitrous oxide plays a critical role in
regulating blood flow through the kidneys, and it is known that the amount
of blood flowing through the kidneys can affect kidney function. L-arginine
levels are often very low in CKD cats.
Nitric acid deficiency in chronic kidney disease
(2008) Baylis C American Journal of Physiology & Renal
Physiology 294(1) ppF1-9 explains more about this and states
that restoring nitrous oxide production may slow the progression of kidney
disease.
Role of L-arginine in the pathogenesis
and treatment of renal disease (2004) Cherla G and Jaimes EA
Journal of Nutrition 134 pp2801S-6S found that l-arginine
supplementation may be helpful or harmful in CKD. It appears to be
detrimental in cases of
glomerulonephritis. See the
Research page for more information on feline research into this issue.
I would not
supplement l-arginine without your vet's approval.
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.
Astro's Protein Powder
The maker of
Astro's CRF Oil also
offers Astro's CRF Protein Powder, though it is not advertised on the
website. It was apparently tested on 24 cats and 11 dogs. The supplement is 96% amino acids made from
wild, deep sea white fish which is enzymatically pre-digested (fish protein
hydrolysate) so the amino acids are
very low molecular weight and therefore need no processing by the digestive
tract. In other words, the product apparently creates very little nitrogenous waste.
It is intended to counteract some of the side effects of low protein diets
in CKD patients (muscle and weight loss and malnutrition). It can be used in conjunction with
Astro's CRF Oil, or added to prescription kidney diets to supplement protein
and calorie intake without placing extra strain upon the kidneys.
The powder is
odourless and water soluble. Ideally it should be given about twenty minutes
before food - it can be mixed with
water and syringed in or offered as is in a bowl (apparently some cats like
the taste and will eat it like this). The recommended dose is a quarter of a tsp per 10lb (4.5kg) of cat
1-2 times a day. It costs US$32.95 plus shipping costs for a 100g jar which
would last 2-3 months for most cats.
I am not aware
of any studies into the use of fish protein hydrolysate in CKD patients
but it appears to be helpful with other conditions.
Reparative properties of a commercial
fish protein hydrolysate preparation
(2005) Fitzgerald AJ, Rai PS, Marchbank T, Taylor GW, Ghosh
S, Ritz BW, Playford RJ Gut 54 pp775-781 found that fish
protein hydrolysate significantly reduced gastric injury in rats and
concluded "Fish protein hydrolysate possesses biological activity when
analysed in a variety of models of injury and repair and could provide a
novel inexpensive approach for the prevention and treatment of the
injurious effects of non-steroidal anti-inflammatory drugs and other
ulcerative conditions of the bowel." Another study,
Fish protein hydrolysate reduces plasma total
cholesterol, increases the proportion of HDL cholesterol, and lowers
Acyl-CoA:cholesterol in liver of Zucker rats (2004) Wergedahl
H, Liaset B, Gudbrandsen OA, Lied E, Espe M, Muna Z, Mørk S and Berge RK
Journal of Nutrition 134 pp1320-7, concluded that fish protein
hydrolysate "may have a role as a cardioprotective nutrient."
I have heard
from a couple of people who have used this product and are happy with it.
They say it has increased their cats' appetites. The best way for cats to
take in the correct balance of amino acids is normally from eating a
complete food designed for cats, but if you do want to try this product,
run it by your vet first. It can be obtained by going to
Astro's CRF Oil and emailing the
manufacturer.
Vitamins
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If your cat is eating prescription food,
in principle additional vitamins should not be necessary, since suitable extra vitamins
are added to these foods. However, if your cat is not eating these foods, additional vitamins may be necessary.
Vitamin B is helpful for most CKD cats regardless of whether they are eating
or not, and is particularly important for cats who are anaemic.
Do not give vitamins to your cat without your vet's
approval because excess vitamin intake can be very dangerous.
The National Academy of Science gives
guidelines on the daily vitamin requirements of cats.
Vitamins A and D
These vitamins are fat soluble, and are stored in
the body rather then excreted. For this reason, there is a risk of toxicity
when supplementing these vitamins. Vitamins A and D also promote
calcification, which is a risk with CKD cats who have a tendency towards
calcification anyway.
In any event, deficiencies in these vitamins are
extremely rare, so it is highly unlikely that your cat requires
supplementation of any kind; plus care should be taken when considering the
use of multi-vitamin tablets, which may contain these vitamins.
Feeding the aging heart
(2010) Freeman LM & Rush JE
Nestlé Purina Companion Animal Nutrition Summit 2010 Focus on Gerontology
states "cod liver oil should not be used to provide omega-3 fatty acids
because it contains high levels of vitamins A and D, which can result in
toxicity."
Dr Katherine James
mentions (Section K, Dietary Management) that Vitamins A and D may cause
toxicity in CKD cats.
DVM News Magazine
states on page 2 that fat soluble vitamins should not be given to
excess.
Vitamin B
Although Vitamin B is commonly referred to as if
it were a single vitamin, there are actually a number of B vitamins. These
are essential vitamins, which means that they cannot be manufactured in the
cat's body, so must be obtained from external sources (from food or a
supplement).
B vitamins are water-soluble, so are
often lacking in CKD cats, who lose much of their Vitamin B through
urination. Cats who are not eating much will also probably not be taking in
enough B vitamins.
B vitamins are so important for CKD cats that there is a
separate page about them.
Vitamin C
Additional vitamin C is not usually a good idea for CKD
cats, because it is acidifying and CKD cats already have a tendency towards
acidosis. Medline
Plus mentions that Vitamin C may also interact adversely with
products containing aluminium, such as
phosphorus
binders.
Vitamin C-induced hyperoxaluria causing reversible
tubulointerstitial nephritis and chronic renal failure: a case report
(2007) Rathi S, Kern W & Lau K Journal of Medical Case Reports 1 p155 reports on a case where a man developed CKD after taking large
doses of Vitamin C, which proved to be reversible following proactive
treatment and stopping the Vitamin C.
In any event, unlike humans, cats are able to
produce their own Vitamin C, so it is usually unnecessary to add it to their diet. However,
one study did find that using Vitamin C as an antioxidant in conjunction
with other vitamins did appear to be effective. See
Treatments for more information on this study.
Vitamin E
Vitamin E is an
antioxidant, and studies are
taking place into the role of antioxidants in improving health.
Addressing age-related changes in feline digestion
(2010) Patil AR & Cupp CJ
Nestlé Purina Companion Animal Nutrition Summit 2010 Focus on
Gerontology
states "if Vitamins E & B12 are at low levels, then
processing of fat and protein are likely compromised in older cats."
If you are giving fish oil-based essential fatty acids,
Vitamin E is also often given in order to avoid steatitis. See
essential fatty acids for more
information.
Vitamin E Supplementation Study
Vitamin E is being investigated as a possible treatment for anaemia.
The Winn Feline Foundation
gave a grant to
Colorado State University
in 2010 for a study
into "Vitamin E as a Novel Treatment for the
Anemia of Feline Chronic Renal Failure."
Vitamin E was selected for its antioxidant properties. As at October 2011
the study is still ongoing, and your cat may be eligible to participate,
see the
Research Participation
page.
I will report on the study findings once it is
completed. In the meantime, please do not
supplement Vitamin E without your vet's approval.
Water
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Water is critical for
CKD cats. In order to
maintain hydration, a cat generally needs around 24-30ml of water per pound
bodyweight per day (though this amount will be affected by activity levels
and climate). This means that a 10lb (4.5kg) cat would require 240-300ml of water a
day (a cat in congestive heart failure may need less).
The cat does
not need to obtain this by drinking alone. If you are feeding canned food,
which contains a lot of water, that will make a sizeable contribution to
total intake.
Effects of feeding frequency on water intake in cats
(2005) Kirschvink N, Lhoest E., Leemans J. Delvaux F, Istasse L,
Gustin P, Diez M Journal of Veterinary Internal Medicine 19
p476 found that cats fed more frequently increased their fluid intake.
Cats in the wild do not eat and drink in the same
place. Therefore it is better not to put the water bowl next to the food
bowl. Some cats don't like a narrow bowl where their whiskers touch the
side, so experiment, and also consider using a water fountain (see below).
Some people find placing ice cubes made from low sodium
tuna water in their cat's water bowl encourages their cat to drink more. You may also wish to give your cat homemade
chicken broth to drink.
With a CKD cat, it makes a lot of sense to have more than
one water source. We used to just have one bowl of water out but once Thomas
was diagnosed we switched to three, including one placed upstairs so Thomas
didn't have to go too far for a drink in the night.
Some people give their cat bottled or distilled
water. The taste of chlorine in normal tap water doesn't taste too good to
cats, so this is worth considering but not essential. Some types of
distilled water have a low pH level, and the extra acidity in these products
is not appropriate for CKD cats, who tend towards acidity anyway. We give our cats
filtered water, at room temperature, and change it several times a day
(changing the water so frequently is not necessary with water fountains, see
below)..
Cats on
subcutaneous fluids may drink less, because some of their hydration needs
are being met through the fluid administration. This is not normally
something to worry about, though ensure you don't see other symptoms that
might, taken together, indicate
crashing.
Daily water requirements and needs for cats
(2011) Peterson ME discusses feline water needs.
Hill's Pet Tails Monthly Newsletter (2011)
explains why cats may prefer running water and gives tips on increasing your
cat's water intake.
Pet Education has some tips on how to get
your cat to drink more.
About Cats Online
has tips on how to get your cat to drink.
Water Fountains
Many people find water fountains increase their cat's
water intake.
Effect of water source on intake and urine
concentration in healthy cats (2010)
Grant DC Journal of Feline Medicine and Surgery 12(6) pp431-4
found that cats drank a bit more from a water fountain but there was not a
massive difference. This was a short study though. I found my cats needed
time to get used to the fountain, but that they did drink more from it once
they were used to it.
There are three main types of water fountain:
My cats have used the large (deluxe) version of the Fresh Flow for several
years and they love it (see photo above). Some people find the Catit easier
to clean. Any of them should be fine for most cats.
When you first get a fountain, leave it out without water
in for a few days to allow your cats to get used to it. Then add water, but
don't turn it on. Once your cats are drinking from it, turn it on. Be sure
to leave other water sources available until you know your cats are willing
to use the fountain.
Instructables
tells you how to build your own water fountain.
Sixerdoodle Electronics has instructions on
adapting your tap (faucet) with a "cat sensor" so your cat can turn it on
and off himself.
How cats lap: water uptake by Felis catus
(2010) Reis PM, Jung S, Aristoff JM & Stocker R Science
330(6008) pp1231-4 explains how cats use their tongue to lap up water.
Drinking
Fountain Sources
USA
Pampered Pet Mart sells the Drinkwell for
US$34.95.
Valley Vet sells the Petmate Freshflow
Water Fountain in the USA for US$33.95 or US$37.95 for the larger model.
Miles Kimball sells a small water fountain
for US$19.99.
Drs Foster & Smith sell a variety of water
fountains with prices starting around US$20.
Amazon sell the Pioneer stainless steel
model for US$54.30.
Drs Foster & Smith sell the Drinkwell stainless steel
model for US$99.95.
Glacier Point sells a variety of ceramic
fountains.
Bottle Babies
sells freestanding water bottle holders, similar to the water
supplies designed for hamsters etc.
UK
Pet Planet sells the Deluxe
Freshflow Fountain for £51.49.
Pet Planet
also sells the Cat-It water fountain for £22.99.
Amazon UK
sells a variety of water fountains.
Canada
Real Canadian Superstore sells the Petmate
Freshflow Water Fountain in Western Canada for CAN$29.98.
Dino Direct sells freestanding water bottle
holders, similar to the water supplies designed for hamsters etc. Some cats
like this sort of fountain.
Other Dietary Issues
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Free Feeding
The National Academy of Science
has performed in-depth research into canine and feline nutrition. It states
that
"If given free access to food, cats will eat between 12 and 20 meals a day,
evenly spread out over the 24-hour light-dark cycle. It goes against the
nature of the cat to force it to eat only one meal a day."
Effects of feeding frequency on water intake in cats
(2005) Kirschvink N, Lhoest E., Leemans J. Delvaux F, Istasse L,
Gustin P, Diez M Journal of Veterinary Internal Medicine 19
p476 found that cats fed more frequently increased their fluid intake.
Free feeding a CKD cat has an additional benefit, namely that
feeding little and often
may reduce the problem of excess stomach acid, a common problem in CKD cats.
Dry food tends to lend itself quite well to free feeding,
but canned food may be a better choice for CKD cats. If you are out a lot
and wish to free feed canned food, an automatic timed feeder is a good idea.
USA
Drs Foster and Smith in the USA
sell a variety of feeders.
Mighty Pets sells an eight day automatic feeder for US$71.99.
Amazon sells the Catmate for US$39.99.
Fancy Paws
sells a two bowl 48 hour timed feeder for US$35.
UK
Pet Planet sells an automatic feeder in the
UK for £29.99.
Zooplus sells a timed feeder for £24.90.
Dry Food
versus Canned Food
As desert animals, healthy cats do not drink a lot, but
instead they obtain moisture from their prey. A mouse, for example, is
around 60% water. Canned cat foods contain even more moisture than this,
between 75-85% in most cases, so a healthy cat who eats primarily canned
food will not drink much at all.
Issues with Dry Food
Most dry cat foods only contain 8-10%
moisture, so cats who eat dry food do tend to drink more than cats fed on wet
food, but they simply cannot take in as much moisture overall as a cat fed
on tinned food. In
Nutrient Requirements of Cats
(1986) the US Board of Agriculture stated "cats given dry food do not voluntarily consume
water to equal the ratio of water to dry matter of cats given canned diets
containing about 75% moisture."
The carnivore connection to nutrition in cats
(2002) Zoran D
Journal of the American Veterinary Medical Association 221
pp1559-67, states "cats eating commercial dry foods will consume
approximately half the amount of water (in their diet and through drinking),
compared with cats eating canned foods... In older cats that tend to produce
urine with a lower concentration, an increase in water consumption becomes
even more important to avoid dehydration and development of
prerenal
azotaemia".
This does not mean that dry foods cause CKD. In fact,
Apparent total tract energy and macronutrient digestibility and fecal
fermentative end-product concentrations of domestic cats fed extruded, raw
beef-based, and cooked beef-based diets
(2012)
Kerr KR,
Vester Boler BM,
Morris CL,
Liu KJ,
Swanson KS Journal of Animal Science
90(2) pp515-22 found that there was no difference in urine
concentration between cats fed the three types of diet used in the study
(dry food, raw food and home-cooked food). In fact, the cats fed the raw and
homemade diets had higher creatinine levels than the cats fed the dry food,
though still within range (these were healthy cats).
However, whilst many healthy cats seem to manage fine
with dry foods, it may be preferable to give a CKD cat a canned food if
possible so as to reduce the possibility of dehydration. The cat food
manufacturers produce their CKD diets in both a dry and a canned version,
but if you can, try to feed your cat the canned version if at all possible.
Issues with Canned Food
Unfortunately, a recent study,
Epidemiologic study of relationships between
consumption of commercial canned food and risk of hyperthyroidism in cats
(2004) Edinboro CH, Scott-Moncrieff JC, Janovitz E, Thacker HL & Glickman LT
Journal of the American Veterinary Medical Association 224 (6)
pp 879-886, indicates that cats who eat canned food, particularly from
pull-ring cans, appear to be at increased risk of developing
hyperthyroidism. It is thought that this may be related to the lining
used in these tins, bisphenol-A (BPA), a potential endocrine disrupter. It
is therefore probably worth trying to feed your cat food from foil pouches
or plastic trays rather than from tins. If you do use tins, be sure to store
any leftover food in glass containers in the fridge rather than in the tins
themselves.
The Food Standards Agency has more
information on this.
Effect of water content in a canned food in voluntary
food intake and body weight in cats (2011)
Wei A, Fascetti AJ, Villaverde C, Wong RK & Ramsey JJ American Journal of
Veterinary Research 72(7) pp918-23 found that healthy cats fed a canned diet
ate more than cats fed the same diet in freeze-dried form, but took in less
energy and "had a significant decrease in body weight." This is
perhaps
because the amount of water in canned foods makes the cat feel full more
quickly.
Another possible issue with canned food is that some cats
find it harder to eat than dry food. Canned food does not allow cats to
get their teeth into it as with a mouse. They often have to lap canned food
up, almost as if it is liquid. Many cats do this with foods canned in gravy
- my Persians (one of whom is not particularly flat-faced) always seem to
simply lick the gravy and leave the chunks. Again, this may lead to a lower
calorie intake overall. and in severe cases, the cat may go hungry. For this
reason I usually feed pate-style canned food, and as my cats eat and spread
the food all over the bowl, I put it back into little piles at intervals.
For a CKD cat, a possible compromise,
especially with dry food junkies, is to feed them both dry and canned
prescription kidney diets. The dry kidney diets tend to be more acceptable
to many cats than the canned versions, so if you have a dry food addict,
try a dry kidney diet. Some people compromise by feeding a dry renal diet
while they are out at work all day, but they then feed a low phosphorus (but
non-prescription) diet when they are home.
Dry foods and risk of disease in cats
(2008) Buffington CAB Canadian Veterinary
Journal 49 p561-3 states that there is little evidence that dry
food contributes to diabetes or ill health generally in cats.
AAFP-AAHA Feline Life Stage Guidelines
state (page 10) "Both canned and dry food have been found to support
health during all life stages.
The panel examined published peer-reviewed evidence-based studies in
healthy, client-owned cats for any significant health effect of: feeding
canned versus dry food (including contribution to dental health); providing
a variety of foods versus a consistent diet; feeding high protein, low
carbohydrate versus lower calorie and high fiber diets; feeding raw diets;
providing dietary supplements, or access to grass or plants. Based on the
available data, specific recommendations in favor of any of these practices
cannot be made."
With CKD cats, obviously you wish to avoid dehydration as
much as possible, but the most important thing is to keep them eating. If
your cat is a dry food junkie, and is prepared to eat dry prescription food,
I would consider feeding it. You can always add water to the dry food to
make it less dry, though if you do this, you should not leave the food down
for too long because it will spoil. An alternative would be to switch to
semi-moist renal food in pouches.
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This page last updated: 15 October 2012
Links on this page last checked: 06 April 2012
