Nutritional Management of Patients with Cancer

Many owners have questions regarding their pet’s nutritional needs after a diagnosis of cancer. Most available evidence investigating nutritional aspects of cancer is from epidemiological data in people, from in vitro studies, or from rodent models. Such studies have many well-recognized limitations, such as species differences. In addition, cancer is a diverse group of diseases that arise from varied tissue types and that affect the pet in very different ways. Therefore, it can be challenging to provide accurate guidance specific for your pet, although the following general advice may be useful.

What types of diets and supplements have benefits for pets with cancer?

Many nutrients, foods, and diet types have been proposed as having anti- or pro-cancer properties, such as low carbohydrate or high fat, fish oil, carbohydrates, and antioxidants, but unfortunately very few have clinical evidence regarding their beneficial or harmful effects. Few studies have been done to support or disprove these strategies in dogs and cats. For example, the low carbohydrate approach has never been tested in pets with cancer, and there may be risks which make this type of diet a poor choice for some pets.

One commercial diet, which is no longer available, was formulated for dogs with cancer (it is no longer available) and included high concentrations of arginine and omega-3 fatty acids from fish oil. Arginine is an essential amino acid for both dogs and cats, and there is conflicting evidence in people with cancer, where some studies show benefits while others show adverse effects. Population studies in people have linked fish consumption with lower incidence of some types of cancer, and some studies in rodents and in cells have shown some potential anti-cancer effects of omega-3 fatty acids (tumor growth, prevention of cancer cachexia, normalizing lactate concentration). Small clinical trials have tested the now-discontinued, high arginine, high omega-3 fatty acid diet in dogs undergoing chemotherapy for lymphoma or radiation therapy for nasal carcinoma. These studies showed some positive effects including longer survival times in some dogs with lymphoma, as well as lower blood concentrations of inflammatory compounds in some dogs with nasal tumors.

Supplements such as antioxidants, phytonutrients, or other compounds are often promoted and used in pets with cancer; however, there is a lack of scientific support for this practice, and safety is a major concern. In general, supplements are not well-regulated, and proof of benefit and safety are not required prior to market. Several studies have shown that supplement products may not contain what is claimed on the label, and they may be contaminated with toxins such as lead. In addition, excessive intake of certain nutrients and potential interactions with medications are both important considerations. Ideally, all supplement products should have strong evidence of benefit, safety, appropriate dosage, bioavailability, and quality control; however, unfortunately this is information not commonly provided by manufacturers.

Overall, there is no strong evidence to support that any specific diets or supplement strategies can successfully prevent the development of cancer or can slow its progression. We often recommend specific doses of omega-3 fatty acids for individual pets, but the primary goals for feeding pets with cancer are to meet their calorie needs and ensure the diet is balanced.

My pet will not eat!

Your pet may not want to eat well during treatment, due to the cancer, medications, or other therapies. Factors that impact appetite should be addressed, such as pain, stress, dehydration, and other comfort issues. Avoid giving disliked medications in food or at least in the main diet. Changing the bowl type (consider using a plate, for example), feeding location, diet flavor, diet temperature, diet moisture level, or the person who feeds the pet can help break negative associations that promote food aversions. In some cases, your veterinarian may recommend medications to stimulate appetite. Feeding tubes can also help ensure your pet is getting adequate calories and essential nutrients as well as water and medications.

Are homemade diets better?

Some owners of dogs and cats with cancer may switch to a homemade diet due to concerns regarding commercial pet foods. There is a lot of misinformation on the internet that suggests that feeding commercial products causes cancer or is not ideal for pets with a cancer diagnosis. These claims are untrue, but a homemade diet can be an appropriate option for your pet. Strictly following a recipe is necessary to avoid problems, and homemade diets tend to be more expensive as well as more time consuming. In addition, unfortunately, most homemade diet recipes in books or online are not balanced or are outdated and could cause harm to your pet. If you wish to cook for your pet, a customized approach is best so that your pet’s individual needs are met. Please contact our Nutrition Service for an appointment: Ph: 530-752-7892; Email: nssvetmed@ucdavis.edu.

What about raw diets?

Raw pet diets are increasingly popular in some areas and are sometimes recommended by veterinarians. Proponents proclaim many health benefits associated with raw diets, and may state that canned and kibble commercial diets are harmful. However, despite these claims, there remains no scientific support for any of the proposed benefits, or to suggest that kibble and canned are harmful. There is some evidence of increased digestibility of specific raw diets compared to other specific diet types; however, this is primarily related to the fiber content, and the practical advantage is simply smaller stool which is not a health benefit. Overall, there have been no studies that demonstrate any long-term health benefits of raw diets compared to other types of pet food.

On the other hand, there are documented risks of raw diets. Potential disadvantages will vary with individual raw diet and its particular attributes. However, the primary concerns are nutritional adequacy (excesses and/or deficiencies in essential nutrients) and contamination with pathogenic microorganisms (bacteria and parasites). A related but equally important concern specific to the use of whole bones is the significant risk of fractured teeth as well as gastrointestinal obstructions and perforations. 

Nutritional adequacy is a concern for both commercial and homemade raw diets. There are very few commercial raw diets that have undergone testing for nutritional adequacy, and many have not been formulated to be complete and balanced.

An additional risk is contamination with bacteria that cause disease in pets and people. Raw meat, fish, eggs, and dairy products are well documented to be common sources of such pathogens. There have been numerous recalls of commercial raw pet foods due to pathogenic bacteria despite the use of high-pressure pasteurization, freezing, freeze-drying, and other techniques by some manufacturers. However, there are also frequent safety recalls due to contamination of raw meat from supermarkets, so foods intended for humans are not necessarily safer. Of particular concern is that antibiotic resistance in these bacteria appears to be a worrisome and ongoing issue in raw pet diets.

It is an often-repeated myth that animals do not become sick when consuming diets contaminated with Salmonella or other pathogens. There are many documented incidences of pets becoming ill from contaminated diets. Additionally, pets who do not develop clinical illness when fed contaminated products still introduce a risk to humans and other pets in the environment through shedding of organisms in the feces and contamination of feeding bowls and surrounding environment. Feeding of raw diets is a documented risk factor for fecal shedding of Salmonella, E. coli, and Campylobacter in healthy dogs. One study showed that dogs intentionally fed a single meal of Salmonella-contaminated raw meat shed the bacteria in their feces for up to two weeks. This issue is a particular concern for patients with cancer, since the underlying disease as well as the treatment may result in immunosuppression which increases the risk of illness.

Importantly, there are now several documented incidences of illness and even death in people exposed to pets fed raw pet food or to the diet itself. Children, seniors, and immunocompromised individuals are at the greatest risk of adverse effects from exposure to pathogenic zoonotic bacteria. Some evidence suggests that routine hygiene efforts may not adequately control risk. One study demonstrated that even scrubbing with soap, soaking in bleach solution, and/or using a dishwasher did not kill a significant number of bacteria on Salmonella-contaminated stainless steel and plastic pet food bowls.   

Given the lack of any documented nutritional advantages and the strongly documented risks, we do not recommend feeding raw diets to dogs and cats. Any of the associated benefits, such as decreased stool volume, high palatability, control over ingredients, and others, can be safely achieved with the use of a properly formulated, balanced, home-cooked diet. Properly cooking the diet as well as ensuring adequate concentrations of all essential nutrients helps to control the risks yet still meet the desires of owners not interested in feeding canned or kibble.

How do I choose a commercial diet?

Our advice for choosing brands is to stick to those made by large, experienced manufacturers who invest in and publish research, have comprehensive quality control including nutritional adequacy testing, have qualified nutritionists on staff (board certified veterinary nutritionists or PhD companion animal nutritionists), etc. There is a list of these guidelines from the World Small Animal Veterinary Association: Global Nutrition Committee (the Committee’s Nutrition Toolkit is easily found online).

These guidelines encompass a range of brands to meet most philosophies, price points, store types, and marketing categories. Your pet’s primary care veterinarian or VMTH clinician can provide guidance on diet choices. If you wish to discuss this in more detail, or if your pet has more complex medical issues, please contact our Nutrition Service for an appointment: Phone: 530-752-7892; Email: nssvetmed@ucdavis.edu.

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