Cancer is common in pets and may result in metabolic changes that can lead to malnutrition.1 As cancer progresses, signs include decreased appetite, lethargy and weight loss, and, in advanced stages, a loss of body fat and lean muscle mass. Recovery or remission is associated with improved clinical status; however, metabolic alterations may persist. The metabolic changes and accompanying malnutrition can decrease quality of life and impair response to treatment.
“The most important dietary consideration for canine and feline oncology patients is that the ration is palatable and eaten, otherwise it has no benefit,” according to the 2016 American Animal Hospital Association (AAHA) Oncology Guidelines for Dogs and Cats.2 For pet parents, seeing a decreased appetite can indicate a poor quality of life, and they may choose to have their pets euthanized at this point.
Food acceptance is driven by the sensory properties of food such as aroma, texture, and flavor. Pets may be initially attracted to a food primarily based on its scent; however, texture plays a crucial role and ingredients greatly influence taste perception. Most palatability research is proprietary; however, there is an extensive body of work evaluating factors that influence acceptance of foods by pets. Shape, texture, density, aroma, taste enhancers, processing techniques, and other technical aspects of producing food can be used to develop and manufacture highly palatable foods.
Energy balance (caloric intake)
In adult dogs and cats, the prominent clinical feature of cachexia is weight loss, which is associated with decreased quality of life and poor prognosis.1 Studies have shown weight loss and being underweight negatively affects survival in dogs and cats with cancer.3,4,5 The cause of weight loss can range from inappetence, increased metabolic rate attributable to cancer burden, changes in taste preference, negative effects of cancer treatment, or alterations in host metabolism that impair utilization of key nutrients.
It is vitally important to maintain a positive energy balance via adequate caloric intake in pets with cancer so they do not begin to utilize glycogen stores, adipose tissue, and dietary protein to compensate. The simplest way to increase the energy density of the food, and, thus, calories, is to add fat.
It is suggested that fat be 25 to 40 percent of the dry matter content of the food in pets with cancer.6 An exception is pets with known fat sensitivities, such as pancreatitis or hyperlipidemia, which should be managed with lower-fat foods.
Protein and L-carnitine
Because cats and dogs do not have storage reserves of protein, any physiological state that results in a negative nitrogen balance causes a loss of normal functions performed by protein. Protein malnutrition may negatively affect the immune system, gastrointestinal (GI) function, and other protein-dependent processes. Loss of lean mass, a late sign of protein malnutrition, usually is attributed to increased turnover of protein induced by cancer cells. However, other nutrient deficiencies can contribute to decreased muscle mass. One such nutrient is L-carnitine, which has been shown to be deficient in people with advanced cancer.7
Offering food with increased amounts of highly digestible protein is a logical choice for pets with cancer.8 This provides amino acids that may be utilized to help blunt nitrogen losses attributable to metabolism changes induced by cancer and its management. Recommended levels of protein in pets with cancer are 30 to 45 percent (dry matter) for dogs and 35 to 45 percent (dry matter) for cats, except for pets with kidney disease and some liver diseases.9
In addition to the absolute amount of amino acids available in food, the correct balance is also needed to promote efficient protein synthesis. Other nutrients, such as L-carnitine, may help spare lean muscle mass by promoting fat metabolism and reducing protein turnover.10
Finally, for adequate amounts of high-quality protein and balanced amino acids to support muscle mass, a positive energy balance must be maintained. Ensuring adequate caloric intake is still the most important aspect of nutritional support for pets with cancer.
Because of metabolic alterations in cancer patients (e.g. increased lactate, insulin resistance), it has been suggested that foods should contain less than 25 percent digestible carbohydrates.6,9 This is based on data from dogs with specific cancers and treatment regimens, and the assumption the Warburg Effect (where cancer cells consume glucose and produce lactate) is present, which is not true for all tumor types.11 Further, it has been difficult to prove limiting dietary carbohydrates slows tumor growth even in those cancers that display the Warburg Effect.
As no ideal carbohydrate level has been established, and the potential for insulin resistance exists, it seems reasonable that a moderate level of carbohydrates (20 to 30 percent of dry matter for cats, 25 to 35 percent of dry matter for dogs) would be acceptable in a food supporting pets with cancer. Because pets with cancer may have difficulty digesting key nutrients (due to cancer or cancer treatments), foods with highly digestible macronutrients (including carbohydrates) may be helpful.
Omega-3 fatty acids
Potential beneficial effects of long-chain omega-3 fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in pets with cancer include preserving lean muscle and helping decrease inflammation that occurs as part of the pathogenesis of cancer.6,12 The limited studies in pets with cancer suggest a positive benefit to feeding long-chain omega-3 fatty acids.
Based on available information, it seems reasonable to include omega-3 fatty acids (EPA, DHA) in foods for pets with cancer. This can be accomplished by using marine oils and other ingredients at a moderate ratio of omega-6 to omega-3 (ranging from 3:1 to 5:1).
Pets with cancer may develop GI signs (e.g. diarrhea or constipation) that result from the cancer, its treatment, or the lack of appropriate nutrient support for the microbes in the lower GI tract. Cancer treatment in people has been shown to cause gut dysbiosis.13 Similarly, dogs with lymphoma have been shown to have alterations in fecal microbiota as a result of cancer.14
While there are no consensus recommendations for the amount or type of prebiotic fibers to provide to pets with cancer, recent research has identified prebiotics that are beneficial and can help manage diarrhea in pets.15 For cancer, it seems reasonable that a mix of soluble (fermentable) and insoluble (non-fermentable) fibers in moderate levels may provide the necessary variety needed by the complex ecosystem within the GI tract to help promote a healthy microflora and optimize stool quality.
Evaluation of cancer patients
A nutritional assessment should be performed as a baseline at the initial diagnosis of cancer and at each visit to detect changes in the pet’s condition and the need for adjustments in the nutritional plan. The process can be done quickly, and information can be collected by the veterinary technician or nurse prior to evaluation by the veterinarian. Engaging with pet parents about nutrition helps build relationships between them and the veterinary healthcare team. There are excellent online resources that include descriptions of a nutritional assessment (See: “Key components of a nutritional assessment”), practical tips, and checklists for having nutritional conversations with pet parents, and how to make a specific nutritional recommendation.16,17
Providing nutritional guidance for pet parents
People with pets that have cancer are usually engaged and motivated to do what is best for their pet. Even though they often consult many resources to learn and understand their options, they highly value advice and guidance from the veterinary healthcare team. In one survey of people whose pets had cancer, 96 percent said they trusted their veterinarian’s advice regarding their pet’s healthcare, and 79 percent indicated the same trust regarding nutritional advice.18 In the same survey, 100 percent believed nutrition played an important role in their pet’s health, and 85 percent said they would purchase a conventional pet food that met their pet’s medical needs.18
Because of the interest of pet parents and the importance of proper nutrition for pets with cancer, the veterinary healthcare team is in an ideal position to proactively engage in a nutrition conversation with pet parents at the time of diagnosis. This is an opportunity to discuss and understand their goals (which almost always relate to quality and length of life), answer their questions, inform them about credible online sources of information, and make a specific nutritional recommendation.
Each nutrition support plan should be developed with specific goals in mind and tailored to meet the needs of each pet. General nutritional goals for pets with cancer include preserving lean muscle, minimizing metabolic and GI intolerance to food, and optimizing quality of life.9 It is recommended to begin nutritional support at the time of a cancer diagnosis and continue past remission for at least six to nine months or longer with reasoning that residual alterations in nutrient metabolism associated with the presence of cancer cells persist for a varying period past treatment.9
To increase the likelihood of food acceptance and long-term consumption, it is important to recommend a complete and balanced food with exceptional taste that meets the nutritional needs of each pet with cancer.
Veterinary therapeutic foods have been recommended for pets with cancer instead of over-the-counter foods because therapeutic foods have more accessible nutrient information for the veterinary healthcare team, the digestibility of key nutrients is usually higher, they may be appropriate for GI issues resulting from cancer treatment or concurrent diseases, and some contain specific nutrients or functional ingredients that may be beneficial, such as EPA, DHA, and fiber.19
Catherine Ruggiero, MS, DVM, DACVIM (Nutrition), is a board-certified veterinary nutritionist and scientific communications specialist for Hill’s Pet Nutrition. Dr. Ruggiero completed her doctor of veterinary medicine training at the University of Missouri in 2014. Prior to that, she received a bachelor of science at St. Lawrence University and a master of science in biological sciences at Fordham University. She was an associate veterinarian at a small animal veterinary practice in Upstate New York for just over three years before returning to the University of Missouri to pursue residency training in small animal clinical nutrition. Upon completion of an ACVN residency program in 2019, Ruggiero joined Hill’s Pet Nutrition as a consulting clinician in VCS, and is currently working in Scientific Affairs.
1. Saker, KE. Nutritional concerns for cancer, cachexia, frailty, and sarcopenia in canine and feline pets. Vet Clin North Am Small Anim Pract. 2021;51(3):729-744. https://pubmed.ncbi.nlm.nih.gov/33773650/.
2. American Animal Hospital Association (AAHA), 2016 AAHA Oncology Guidelines for Dogs and Cats. https://www.aaha.org/aaha-guidelines/oncology-configuration/oncology-guidelines/, accessed July 2022.
3. Michel, KE, et al. Evaluation of body condition and weight loss in dogs presented to a veterinary oncology service. J Vet Intern Med. 2004;18:692-5. https://pubmed.ncbi.nlm.nih.gov/15515586/.
4. Baez, JL, et al. A prospective investigation of the prevalence and prognostic significance of weight loss and changes in body condition in feline cancer patients. J Feline Med Surg. 2007;9:411–417. https://pubmed.ncbi.nlm.nih.gov/17451991/.
5. Romano, FR, et al. Association between body condition score and cancer prognosis in dogs with lymphoma and osteosarcoma. J Vet Intern Med. 2016;30(4):1179-86. https://pubmed.ncbi.nlm.nih.gov/27279003/.
6. Saker, KE and Selting, KA. Cancer. In: Hand, M. S., et al: Small Animal Clinical Nutrition, 5th ed, 2010:587-607.
7. Cruciani, RA, et al. L-carnitine supplementation in patients with advanced cancer and L-carnitine deficiency: a double-blind, placebo-controlled study. J Pain Symptom Manage. 2009;37(4):622-31. https://pubmed.ncbi.nlm.nih.gov/18809275/.
8. Wakshlag, J. Supportive care for the patient with cancer. In: Vail, D. M., et al. Withrow and MacEwan’s Small Animal Clinical Oncology, 6th ed Elsevier, 2019:286-329.
9. Saker, KE. Practical approaches to feeding the cancer patient, Today’s Veterinary Practice. July/August 2014. https://todaysveterinarypractice.com/nutrition/acvn-nutrition-notes-practical- approaches-to-feeding-the-cancer-patient/, accessed July 2022.
10. Varney, JL, et al. L-carnitine metabolism, protein turnover and energy expenditure in supplemented and exercised Labrador Retrievers. J Anim Physiol Anim Nutr (Berl). 2020;104(5):1540-1550. https://pubmed.ncbi.nlm.nih.gov/32557872/.
11. Potter, M, et al. The Warburg effect: 80 years on. Biochem Soc Trans. 2016;44(5):1499-1505. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5095922/.
12. Tanner, AE, et al. Cell proliferation of feline and human breast cancer cell types is inhibited by pomegranate juice. J Anim Physiol Anim Nutr. 2008;92(2):221–3. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1439-0396.2007.00789_7.x
13. Deleemans, JM, et al. The use of prebiotic and probiotic interventions for treating gastrointestinal and psychosocial health symptoms in cancer patients and survivors: a systematic review. Integr Cancer Ther. 2021. https://doi.org/10.1177/15347354211061733.
14. Gavazza, A, et al. Faecal microbiota in dogs with multicentric lymphoma. Vet Comp Oncol 2018;16(1):E169-E175. https://pubmed.ncbi.nlm.nih.gov/29152844/.
15. Jackson, MI and Jewell, DE. Balance of saccharolysis and proteolysis underpins improvements in stool quality induced by adding a fiber bundle containing bound polyphenols to either hydrolyzed meat or grain-rich foods. Gut Microbes. 2019;10(3):298-320. https://pubmed.ncbi.nlm.nih.gov/30376392/.
16. American Animal Hospital Association (AAHA), Nutrition is Vital (Elements of a Nutritional Assessment), 2021. https://www.aaha.org/practice-resources/pet-health-resources/nutritional-resources/, accessed July 2022.
17. World Small Animal Veterinary Association (WSAVA), Global Nutrition Guidelines, 2022. https://wsava.org/global-guidelines/global-nutrition-guidelines/, accessed July 2022.
18. Rajagopaul, S, et al. Owners’ attitudes and practices regarding nutrition of dogs diagnosed with cancer presenting at a referral oncology service in Ontario, Canada. J Sm Anim Pract. 2016;57(9):484-9. https://pubmed.ncbi.nlm.nih.gov/27357412/.
19. Raditic, D and Gaylord, L. Nutrition for small animal cancer patients. Today’s Veterinary Practice. 2021;January-February:16-21. https://todaysveterinarypractice.com/nutrition/nutrition-for-small-animal-cancer-patients/, accessed July 2022.