Nutrition can play a significant role in the management of dogs and cats with cancer. Pets with cancer could experience weight loss because of decreased intake of food secondary to physical obstruction (e.g., a tumor growing within the oral cavity), or because of decreased appetite secondary to side effects from various treatments.
However, some pets with cancer will lose weight even though they are ingesting adequate amounts of calories per day. "Cancer cachexia" is the specific terminology that applies to weight loss despite adequate nutritional intake seen in patients with tumors. The weight loss comprises both the loss of lean body mass and fat stores. This can lead to problems with healing wounds, immunosuppression, and organ dysfunction.
Surprisingly, studies indicate that many pets with cancer are actually overweight or obese at the time of their diagnosis. It is unclear whether over conditioning contributes to the development of cancer. The nutritional management of these patients can be a challenge. There are many concurrent health risks associated with obesity, including musculoskeletal disease, diabetes, glucose intolerance, and immunosuppression. Therefore, weight loss in these patients would certainly be beneficial for long-term survival. However, balancing planned weight loss in the face of treatment is difficult, and the typical weight-loss plans used for healthy animals are not appropriate for our cancer patients.
The major building blocks of any diet include carbohydrates, fats, and proteins. Several different metabolic alterations in these nutrients have been discovered in pets with cancer:
With regard to carbohydrates, tumor cells readily use glucose as a source of energy, and the by-product of this metabolism is lactate. Lactate is a cellular waste product that can be converted back to glucose, but this occurs at the net expense of energy by the animal, contributing to a cachectic state. Dogs with various types of cancers have elevations in blood lactate levels and elevated blood insulin levels, compared to healthy control dogs, and these changes do not always resolve following treatment of the tumors.
In one study, dogs with cancer had alterations in several different blood levels of amino acids, the building blocks for protein synthesis. Like carbohydrates, these alterations in amino acid levels did not normalize following removal of the tumor, suggesting that long-lasting effects in protein metabolism are caused long before treatment is initiated. This could contribute to immune system dysfunction and poor wound healing.
Similarly, another study showed that dogs with cancer have altered lipid profiles that favor the catabolism of fat tissue, which may contribute to the development of cachexia. In one study, a small number of dogs with lymphoma were fed an experimental diet supplemented with enhanced levels of n-3 fatty acids. Results indicated for a specific subset of dogs with lymphoma (Stage III only undergoing treatment with single-agent doxorubicin chemotherapy), dietary supplementation with n-3 fatty acids contributed to longer disease-free intervals and survival times. In another study, dietary supplementation with n-3 fatty acids decreased radiation-induced damage to the skin and oral mucosa in dogs with nasal tumors.
The ideal nutritional requirements for pets with cancer remains unknown, however as indicated above, we know that these animals show signs of alterations in the metabolism of carbohydrates, fats, and proteins, and that changes in the metabolism of these nutrients will often precede any clinical signs of disease and/or cachexia. Therefore, general recommendations for dietary requirements for cancer patients typically consists of a combination of:
- Small amounts of complex carbohydrates (crude fiber levels > 2.5% of dry matter)
- Minimal quantities of rapidly absorbed simple sugars
- High quality but modest amounts of digestible proteins (30-35% of dry matter for dogs and 40-50% of dry matter for cats)
- High amounts of unsaturated fats (>30% of dry matter)
- Omega-3/DHA essential fatty acid supplementation — consult with your veterinarian for appropriate dosages
These components can be achieved through various commercially available diets or via home cooked diets that have been properly reviewed by a veterinarian.
It is very important to keep in mind that additional research is necessary before making sweeping generalizations regarding the ideal diet to feed a pet with cancer. The optimal dietary requirements will vary based on individual patients’ needs, their type of cancer, and also the presence and severity of concurrent diseases (e.g., diabetes or hyperthyroidism). Many owners are Internet savvy and a quick Google search using the terms "diet, pets, and cancer," returns thousands of websites containing a tremendous amount of information. Unfortunately, most of it is unproven, over-interpreted, and not evidence based.
One of the most important thing I always stress to pet owners is that it’s never a good idea to implement any diet change and/or addition of supplements or nutraceuticals at the same time their pet is scheduled to be starting chemotherapy and/or radiation therapy, as we want to limit the number of variables that could cause adverse side effects. Once the pet has started on their treatment plan — as long as they are doing well — that is the time to consider any kind of a diet modification. Important considerations to make when thinking about any kind of change would be to serve foods that are highly bioavailable, easily digestible, and highly palatable with a good smell and taste, in order to avoid food aversions and encourage appetite.
I also stress to owners that many of the terms used to describe pet foods on labels and in advertising materials are not legally defined. For example, there are no regulatory meanings for the terms holistic, premium, ultra- or super-premium, gourmet, or human grade. Therefore, it is important to be educated about reading labels and not be swept in by some of the claims made by pet food companies regarding the integrity of their products.
I also make it clear to owners that as a medical oncologist, I am aware of research within the field of veterinary nutrition, but I strongly feel expert opinions are best obtained via consultation with a board certified veterinary nutritionist. I urge them to seek information and advice available through the American College of Veterinary Nutrition.
Dr. Joanne Intile