Feeding the Cancer Patient

Research on cancer in dogs and cats continues to advance, and veterinary options for treatment and palliative care are becoming more readily available. However, investigation into nutrition for veterinary cancer patients remains insufficient. Suggestions often concentrate on management of anorexia or cachexia.^1,2 No published feeding trials have studied the effects of diverse nutrient profiles on dogs with cancer or undergoing treatment, with one exception being a study of lymphoma in dogs.^1,3

Despite this lack of research, clients frequently want information about what to feed their pet. Often, they turn to social media or the internet for answers. To be a reliable source of information and recommendations for owners of pets with cancer, veterinary healthcare team members should understand nutritional needs in cancer patients and nutrients to consider when managing cancer.

Prevalence of Cancer

Cancer is common in companion dogs and cats, although it is somewhat less common in cats than in dogs. Neoplastic disease has been found to be the most common deadly pathological process in approximately 90% of canine breeds. It is also reported to be the most common cause of death in dogs older than 1 year, with an incidence more than 3 times that of traumatic injury.^4,5 In the United States, a higher prevalence of cancer has been seen in golden retrievers. A North American study found the top 5 breeds with the highest proportion of deaths from cancer to be Bernese mountain dog, golden retriever, Scottish terrier, Bouvier des Flandres, and boxer.⁵ In Sweden, a retrospective study found that boxers and Bernese mountain dogs were among breeds significantly overrepresented as having died of cancer.⁶

Nutritional management of dogs and cats with cancer is part of a multimodal approach to therapy that the veterinary team should consider when initiating treatment. Providing appropriate nutrition may improve quality of life, enhance the effectiveness of treatment, and increase survival time. Nutrition also allows the pet owner to be involved in the management of their beloved family member.⁷

Nutritional Assessment

Nutritional status should be assessed for every cancer patient. At minimum, the nutritional assessment should include:

• Type of diet
• Amount being fed
• Feeding method
• Patient appetite
• Client attitude toward the patient’s current nutritional regimen

The veterinary nurse should use open-ended questions during the assessment to elicit more information from the pet owner than a “yes or no” answer would provide.

It is important to note the patient’s current and past body weights, body condition score, and muscle condition score.¹ These tools aid in the identification of patients that may be malnourished and/or inappetent. In human cancer patients, nutritional assessments have found that 40% to 80% of patients experience varying degrees of malnutrition depending on type of tumor, location, stage, and treatment plan.^1,8 The same can be said of veterinary cancer patients, thus the importance of a nutritional assessment.

Metabolic Alterations in Patients with Cancer

Veterinary healthcare teams must be vigilant to help identify cancer cachexia. Cancer cachexia is a paraneoplastic syndrome manifested by weight loss and a decrease in body condition despite adequate nutritional intake.⁹ The numbers of dogs and cats with cancer cachexia are not fully known, but it is imperative for veterinary nurses to remember cachexia when obtaining a patient history and body condition score for a pet with cancer.

The metabolic alterations described below have been identified in human and canine cancer patients and have been associated with cachexia, a decreased response to therapy, a decreased remission rate, and an increased mortality rate.⁷

Carbohydrate Metabolism

Studies have shown that dogs with lymphoma and many other malignant diseases have a significant alteration in carbohydrate metabolism.^10,11 Tumors preferentially metabolize glucose (carbohydrates) for energy and form lactate (lactic acid) as an end product. Therefore, the host must expend energy to convert lactate back to glucose. This results in a net energy gain by the tumor and a net loss by the host. The process causes dogs with cancer to not only lose energy but also have elevated blood lactate and insulin levels (i.e., laboratory evidence of altered carbohydrate metabolism). Additionally, it is important that healthcare team members avoid administering fluids that contain glucose or lactate to pets with cancer.

Protein Metabolism

Patients with cancer and cachexia experience an alteration in protein synthesis that is the primary factor in loss of weight and muscle mass.^7,12 Concurrently, in an effort to support tumor growth, skeletal muscle protein breakdown, liver protein synthesis, and whole body protein use synthesis all increase.⁷ If protein intake does not keep pace with use, immune response, gastrointestinal function, and wound healing are affected.

Fat Metabolism

Catabolism of adipose tissue is the second major feature of cachexia in a variety of chronic diseases, including cancer.^2,7,12,13 A decrease in fat synthesis or an increase in lipolysis can deplete fat stores. Studies in animal models suggest that tumor production of lipid-mobilizing factor may account for loss of body fat, especially when combined with decreased food intake.

Unlike host tissues, cancer cells have difficulty using lipids as a fuel source compared with soluble carbohydrates and protein.^7,14,15 This finding has led to the hypothesis that foods relatively high in fat, particularly omega-3 fatty acids, may benefit dogs with cancer more than foods relatively high in carbohydrates.¹⁵

Nutrients to Consider in Cancer Management

When it comes to nutrition for pets with cancer, the veterinary healthcare team must ensure that caloric and vital nutrient needs are met. The primary goal with cancer patients is to maintain weight. It is imperative to maintain an open dialogue with pet owners, who tend to feed more treats—and sometimes more food—after a cancer diagnosis because it is “something they can do to help their pet feel better.” However, this may lead to the pet becoming overweight, which may make the cancer worse. The veterinary team must also stress the importance of specific nutrients to the pet owner and explain that adding more meat and other foods to the pet’s normal diet, or making the pet’s food at home, can lead to nutrient deficiencies that may make it harder for the pet to fight cancer.

Nutrition recommendations should be specific to each cancer patient and based on the nutritional assessment of that patient. The veterinary team should evaluate each patient with cancer and develop a treatment plan that includes a personalized nutrition plan to be introduced, monitored throughout treatment, and changed as needed.

Soluble Carbohydrates and Fiber

Historically, it has been suggested that soluble carbohydrates should make up less than 25% of a cancer patient’s food on a dry matter basis (DMB) because soluble carbohydrates may be poorly used by animals with cancer and, as mentioned above, tumor metabolism of carbohydrates for energy contributes to increased lactate production. More recent recommendations to feed a low- or no-carbohydrate diet are attempts to “starve” cancer cells, based on research published in the 1920s that found that compared with normal tissue, tumors showed unusually high rates of glucose uptake and lactate production even in the presence of oxygen.¹

However, research performed since has revealed that depriving tumors of nutrients is not as straightforward as limiting carbohydrates. Some cancer cells possess metabolic flexibility, meaning they adapt their carbohydrate, fat, and protein metabolism according to nutrient availability, tumor microenvironment, and cancer treatments.^1,16-19 This ability to adapt makes monitoring and adjusting the nutritional plan for each cancer patient a critical part of management.

With regard to fiber, veterinary nurses must remember that soluble and insoluble fiber sources are important to help maintain intestinal health, especially in animals undergoing chemotherapy, radiation therapy, or surgery. Increased dietary fiber may help prevent and resolve abnormal stool quality (e.g., soft stools, diarrhea) encountered when changing from a high-carbohydrate commercial dry food to a high-fat commercial or homemade food.

Protein

Because patients with cancer experience increased protein metabolism resulting in loss of lean muscle mass (cachexia), dietary protein should be highly digestible and exceed the level normally used for maintenance of adult animals.^7,15

Arginine is an essential amino acid that may have specific therapeutic value in pets with cancer. The minimum effective level of dietary arginine for animals with cancer is unknown; however, a positive correlation between plasma arginine concentrations and survival in dogs with lymphoma receiving chemotherapy suggests that it is appropriate to provide more than 2.5% arginine on a DMB.¹⁴ Arginine has also been shown to improve immune function in both canine and feline cancer patients, promote wound healing, and inhibit tumorigenesis.^7,14 Cats should receive foods with a similar level of arginine (i.e., >2% DMB). l-Arginine can be included in the diet by providing a supplement or a high level of good-quality protein.

Glutamine has several important biochemical roles and is a preferred source of energy for cells with rapid turnover, such as lymphocytes, enterocytes, and cancer cells. It has recently been recognized as a conditionally essential amino acid in certain physiologic states, including stress. Cancer can be considered to elicit a stressful physiologic response. Glutamine has been shown to stabilize weight loss, improve protein metabolism, improve immune response, and improve gut barrier function in rodent cancer models and in human clinical trials.^7,14 Glutamine is best provided by high-quality, high-protein pet foods.

Fat and Omega-3 Fatty Acids

Omega-3 fatty acids may have preventive and therapeutic roles in cancer therapy. Epidemiologic evidence supports the use of omega-3 fatty acids in human patients with cancer. Low cancer rates have been recognized in human populations with high dietary intake of omega-3 fatty acids, which have been shown to reduce the risk of colorectal, prostate, and mammary cancer.^7,14,20 Omega-3 fatty acids increase the immunologic response against tumor cells, increase tumor susceptibility to oxidative stress, and decrease tumor necrosis factor-α production. Additionally, high levels of omega-3 fatty acids have shown clinical benefits, including reduced tumorigenesis, tumor growth, and metastasis, as well as anticatabolic effects.^15,21,22 In one human study, omega-3 fatty acids in combination with arginine were shown to influence clinical signs, increase survival time, provide longer remission time, and improve quality of life.¹⁸

Summary

Nutritional therapy can influence remission time, survival time, and quality of life for cancer patients. Veterinary nurses must ensure that clients understand their pet’s cancer diagnosis and what it means for their pet, and that they accept the recommendations made. Nutrition is one therapy that can be offered to clients to involve them in the treatment process and help their pet live as long as possible and feel better overall.