Cancer-associated weight loss in cats and dogs
Cancer cachexia (a term referring to progressive severe weight loss) is frequently observed in both humans and pets
diagnosed with cancer. Pets with cancer lose weight partly because of lack of appetite and partly because of poor
absorption of nutrients from the digestive tract. Some of the causes for decreased appetite are related to the cancer itself
(for example, tumors may physically interfere with food chewing, swallowing, and digestion process) and some may be
related to the side effects of cancer treatment (for example, some chemotherapy drugs cause nausea and vomiting, and
radiation therapy can cause mouth inflammation).

The severity of weight loss will depend on the tumor type, the stage of the disease and will also vary from one pet to
another. As the cancer alters the pet's sugar, protein and fat metabolism, and 'steals' nutrients from the pet, the pet's body
will be forced to use its own tissues (e.g. fat and muscle) as an alternative source of energy to survive.  Tumors have been
shown to preferentially use protein as energy source at the expense of the host, and use certain amino acids that result in
abnormal amino acid profiles in pets with cancer. When protein degradation becomes higher than protein synthesis, it can
have a negative impact on immune system, function of the gastrointestinal tract and wound healing as discussed in more
detail below.

Impact of malnutrition on a cat or dog with cancer
The impact of severe weight loss can be quite devastating on the pet's quality of life as well as his or her ability to tolerate
and respond to cancer treatments. Progressive cancer cachexia will lead to anorexia (lack of appetite), fatigue, abnormally
low levels of proteins (that can alter metabolism of drugs that your pet may be given), delayed wound healing and tissue
repair, immunosuppression (when the immune system does not function normally), reduction in pulmonary and
cardiovascular function, and ultimately death. Proper nutrition while undergoing cancer treatment is essential to maintain
your pet's strength, improve survival times, quality of life and maximize response to therapy. Adequate nutritional support
was shown to decrease the duration of hospitalization, reduce post-surgery complications and enhance the healing process.

Impact of cancer on metabolism in pets with cancer
There are three basic sources of energy found in food: proteins, carbohydrates (sugars) and fats. Many commercial pet
foods are high in carbohydrate content, which are not ideal to support cancer patients. In one study, dogs with lymphoma
were split into two groups receiving the same quantity of calories but one group was fed high-carbohydrate diet and the
second group was fed high-fat diet. The diet was administered before and after remission with up to five doses of commonly
used chemotherapy drug doxorubicin.  The results showed that lactate and insulin levels from dogs who received high-
carbohydrate diet was significantly higher compared to the dogs fed with high-fat diet, and dogs fed with high-fat diet were
more likely to go into remisision. Therefore, the type of diet that your pet gets can influence response to chemotherapy.

Knowing that tumors preferentially use amino acids, providing high quality amino acids or protein to some pets with cancer
may be of critical importance. Some amino acids also showed a therapeutic benefit, such as arginine, glycine, cystine and
glutamine. For example, adding arginine amino acid to total parenteral nutrition solution decreased tumor growth and
metastatic rate (spread to other organs) in laboratory mice; glycine was shown to reduce kidney toxicity associated with a
commonly used chemotherapy drug cisplatin in dogs; or glutamine was shown to reduce gastrointestinal toxicity associated
with methotrexate chemotherapy drug in cats.

Loss of fat accounts for the majority of weight loss in pets with cancer, and many cancer patients show abnormalities in their
lipid metabolism. These abnormalities have been linked to suppressed immune system, which correlates with shorter
survival times in human counterparts with cancer. In comparison to proteins and sugars, cancer cells have difficulties in
using fats as source of energy, which led to the hypothesis that high-fat diets may be beneficial to pets with cancer
compared to a diet high in simple carbohydrate. In one study, dogs with Stage III lymphoma were fed an experimental diet
designed to enhance the effect of n-3 fatty acids, which was associated with longer disease-free interval and survival times.
In another study,  fatty acids of the n-3 series decreased radiation damage to the skin and mucosa, and improved the
performance status in dogs with nasal tumors.

What to feed cat or dog with cancer
As summarized above, available data suggest that a diet relatively low in simple sugars, with moderate amounts of highly
bioavailable proteins, fiber, and moderate amounts of n-3 polyunsaturated fatty acids may be beneficial for pets with cancer.
However, more research is needed to evaluate in more detail the optimum quantities and ratios of each component to
maximize the benefit. The diets should also go beyond sugars, protein, fat and fiber, and should incorporate other
components such as vitamins and minerals. For a comprehensive review written by Dr. Ogilvie, DVM, DACVIM (Internal
Medicine and Oncology) addressing this topic, please click
here.

The specific diet for your pet will depend on the level of pet's malnutrition, the specific tumor type, what treatment he or she
will undergo, existence of other medical conditions, and overall health of the pet. Some pets with a particular cancer may
require additional nutritional supplements, and pet owners should work closely with their veterinarian and veterinary
nutritionist  to develop an appropriate nutritional plan for their pet during and after cancer treatment. Some veterinary
oncology hospitals now provide nutritional counseling services to help pet owners determine which foods are best suited for
their pet's unique needs. The goal should be to begin nutritional support early on rather than waiting until signs of weight
loss occur.

How to feed cat or dog with cancer
The pet may lose its appetite while undergoing cancer treatment, and nutritional support becomes especially important
during this time. For example,
radiation therapy may temporarily blister the pet's mouth and throat, making swallowing
difficult.
Chemotherapy may cause temporary nausea, decreasing the pet's appetite. Surgery on the pet's mouth may take a
while to heal, preventing the pet from being able to eat and drink. In these cases, alternative methods of feeding must be
applied to continue adequate nutritional support.

Voluntary intake
Voluntary intake of food is the preferred method of feeding, however, the pet's lack of appetite will frequently limit the caloric
intake. As a result, the pet will not meet the minimum nutritional requirements and some form of assisted feeding will have to
be implemented. The first step is to enhance the pet's appetite. This can be accomplished by warming the food to just below
body temperature, enticing the pet with tasty, aromatic foods, and feeding them in a stress-free, comfortable environment. If
that fails, other options include administration of appetite stimulating drugs, use of feeding tubes or intravenous feeding.

Appetite stimulating drugs
The use of drugs is convenient and cost effective, however, special care has to be taken to make sure that the drugs are
actually effective and the pet has indeed increased its nutritional caloric intake. Cyproheptadine or megestrol is usually
effective in stimulating appetite in cats. Diazepam is typically used as a short term therapy in the hospital but not often as
home therapy. Metoclopramide can be used in cats and dogs to reduce nausea associated with chemotherapy or surgery.

Feeding tubes
Feeding tubes are typically used in pets whose intestinal tract is still functional but cannot use their mouths and throats. The
placement of a feeding tube may be either short-term or long-term, depending on the pet's overall condition and nutritional
needs. The pet's overall health and prognosis have to be carefully evaluated prior to insertion of a feeding tube, and the
pet owners should discuss in great detail the risks and benefits of the procedure.

For short term nutritional support (for example after surgery), the veterinarians will typically install the nasogastric feeding
tube, which is placed through the pet's nose down to the stomach. The pet typically wears an Elizabethan collar around its
neck to prevent it from using its paws to move the tube.

For long term nutritional support, the veterinarian can decide to install an esophagostomy tube or a gastric feeding tube.
The esophagostomy tube is placed under short general anesthesia through the side of the pet's neck into the esophagus.
The gastric feeding tube is also placed under general anesthesia, and placed directly into the stomach through an opening
made to the abdomen.Gastric tubes are usually used in pets who need nutritional support for more than seven days.

The veterinarian will prescribe special diet that is specifically formulated for tube feeding. The tube feeding should start very
slowly (to prevent 'refeeding syndrome' which can, in severe cases, lead to cardiovascular collapse and death), and if the
initial recommended regimen is well tolerated, the pet will eventually receive its full caloric intake in 4 to 6 daily feedings.
Some pets can be managed by their owners at home but critically ill pets should be hospitalized during the first few days
after feeding tube installation.

Intravenous feeding
Intravenous feeding is reserved for only a small subset of pets in whom the intestinal tract is not functional or who cannot
undergo general anesthesia for placement of feeding tubes. The pet's condition should be carefully evaluated to ensure
that it fits the subset of animals for whom this type of feeding is appropriate.

Finding a qualified veterinary oncologist to discuss nutritional support for your pet
To locate a qualified veterinary oncologist in your area who can discuss with you appropriate nutritional requirements for
your pet's cancer condition, please visit the "
Locate a veterinary oncologist" section.  

Source
  • Withrow Stephen J, and David M. Vail. Small Animal Clinical Oncology. St Louis: Saunders Elsevier, 2007.
  • Nutrition and Cancer: Frontiers for Cure! by Gregory K Ogilvie, DMV, DACVIM (Internal Medicine and Oncology)
  • Feeding Hospitalized Patients - Help Yourself by Rebecca Remillard, PhD, DVM, Diplomate of the American College of
    Veterinary Nutrition (Angell Animal Medical Center). For a full article, please click here.

Useful online resources about nutritional support in cats and dogs with cancer
Nutritional Support for Cats and Dogs with Cancer
SUPPORTIVE CARE FOR PETS WITH CANCER
© 2007 Pet Cancer Center. ALL RIGHTS RESERVED.
Last updated 4/10/13
Nutritional Management for
Cats and Dogs with Cancer
KEY TAKE-AWAYS
  • Progressive severe weight loss is frequently observed in cats and dogs with cancer.
  • Cancer alters the pet's sugar, protein and fat metabolism, which can lead to decreased quality of life, poor
    treatment response and shorter survival times.
  • Pets with cancer should receive appropriate nutritional care to maximize good performance status,
    improve quality of life and speed up recovery.
  • Nutritional support and therapy is a key component of your pet's cancer treatment plan before
    the pet shows signs of weight loss.
  • See your veterinarian for specific nutritional recommendations for your pet's unique condition.
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PET CANCER CENTER
Comprehensive guide to cancer diagnosis and treatment in cats and dogs