Feeding Your Cat During Cancer Treatment

By Ryan Llera, BSc, DVM; Robin Downing, DVM, CVPP, CCRP, DAAPM

Advances in veterinary awareness and diagnostics not only means cats are now living longer and with a better quality of life than ever before, but it also means the likelihood of diagnosing cancer during a cat’s life has increased. As with people, known carcinogens can have a detrimental effect on cats (e.g., second hand smoke, exposure to ultraviolet rays, and obesity) and are associated with an increased risk of developing cancer.

Cancer not only compromises a cat's quality of life, but it is also the leading cause of non-accidental death in cats. Other diseases are more common (e.g., obesity, chronic kidney disease, allergies), but cancer remains the most common fatal disease. In cats, cancer is also commonly linked to a retrovirus, called Feline Leukemia Virus.

I just learned that my cat has cancer. What now?

Treating and managing cancer in a feline patient is a team effort and involves the primary care veterinarian, the veterinary health care team, veterinary specialists, and (most importantly) the family. The course of treatment varies and depends on the type and progression of cancer, but it may include surgery, chemotherapy, radiation therapy, or a combination of these.

With all cancer management strategies, providing optimal nutrition for your cat is essential. Proper nutrition can support both longevity and quality of life for cats with cancer.

Aside from the tumor itself, are there other changes in the body I should be aware of?

The metabolism of cats with cancer changes over time, passing through four phases:

  • Phase 1 is preclinical, meaning cats show no outward signs of illness although there may be alterations in some blood test parameters. There are no blood tests that can be used to screen and diagnose cancer in this early stage.
  • In Phase 2, cats begin showing clinical signs of cancer. These may include decreased activity levels, decreased appetite, and possible weight loss. Some signs in this phase are secondary effects resulting from radiation therapy, surgery, or chemotherapy.
  • In Phase 3, cancer-related metabolic changes result in a significant loss of muscle and fat stores. This profound loss of body condition is called cancer cachexia and may be reversible if remission is achieved.
  • Phase 4 changes occur in remission. Despite eliminating the cancer, metabolic changes may persist which makes a full recovery challenging. Nutrition plays an important role in managing these metabolic changes.

How will cancer treatments affect my cat’s nutritional status?

The metabolic effects of cancer will persist after treatment. By anticipating the potential negative nutritional impacts of cancer treatment, you can adjust your cat's nutrient profile and potentially avoid some of these negative side effects.

The effects of surgery depend on the type of surgery performed. Head and neck surgery, for instance, may make it difficult for your cat to eat. A feeding tube can be lifesaving in this case and can be used long term if needed. Cats undergoing stomach or intestinal surgery, on the other hand, will generally benefit from food that is designed to prevent nausea and is easily digestible.

Chemotherapy affects rapidly reproducing cells. Cancer cells are the intended target, but the cells that line the stomach and intestines are also rapidly dividing and can be affected. The result is often nausea, vomiting, and diarrhea which typically decreases a cat's appetite and food consumption.

The nutritional complications of radiation therapy will vary depending on the location and dose of treatment, as well as its reaction to other simultaneous cancer treatments. Head and neck radiation is known to decrease the production of saliva and can cause ulcers in the mouth and throat, preventing normal eating. Radiation to the chest and upper abdomen can cause nausea and vomiting. Lower abdomen radiation can cause diarrhea. In any case, radiation therapy is typically performed over successive days while the cat is under general anesthesia. Since cats must fast before anesthesia, the timing and calorie density of feeding prior to and after their treatment is important in helping your cat avoid weight loss and deconditioning.

What nutritional changes should I now consider?

Tumor cells love carbohydrates. Tumors use carbohydrates to promote cancer cell growth, so high levels of carbohydrates in a cat's food will actually feed the tumor and starve the patient! Research suggests that cats with cancer should eat a nutrient profile with no more than 25% carbohydrate on a dry matter (DM) basis. Unfortunately, the majority of feline adult maintenance formulations are far higher than that in carbohydrate content.

On the other hand, cancer cells have a difficult time using fat as an energy source, so foods that are relatively high in fat and low in carbohydrate may benefit cats with cancer. In addition, higher levels of omega-3 fatty acids may exert an anti- tumor effect. While additional research is needed, it is recommended that feline cancer patients eat a ration with 25-40% DM fat and 5% DM or greater of dietary omega-3 fatty acids.

"On the other hand, cancer cells have a difficult time using fat as an energy source, so foods that are relatively high in fat and low in carbohydrate may benefit cats with cancer."

Cancer does cause imbalances in protein metabolism, but protein intake is critical to maintain lean body mass. Dietary protein levels for cats with cancer should be higher than those in a normal adult maintenance formulation, but only if the liver and kidneys are functioning normally. The current recommendation for feline cancer patients is a protein level of 40-50% DM.

Your veterinarian will help you choose a nutrient profile, formulation, quantity, and delivery method (particularly if there is a feeding tube involved) that fits your cat's specific needs. While there are no specific diets for cancer patients, there are several therapeutic diet formulations, including some canned kitten foods, with nutrient profiles that are close to the cancer-specific recommendations. One such diet is Hill's® Prescription Diet® a/d®.  Homemade diets must be nutritionally balanced, and that is challenging to accomplish. In any event, it is always best that a cat with cancer eat something rather than nothing. Your veterinarian can help you choose the best option for your cat.

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