Why do pets with cancer lose weight?
Many pets with cancer develop cachexia, which is a syndrome in which the animal loses weight and muscle mass due to the increased metabolic needs placed upon the body by the tumor cells. Cancer changes how the body metabolizes and utilizes carbohydrates, protein, and fat, so even an animal with a normal appetite may develop cachexia.
Tumors prefer to use glucose (sugar), which comes from carbohydrates, for energy. Veterinary cancer specialists believe this alters carbohydrate metabolism in dogs with cancer. When glucose is metabolized by the tumor cells, lactate (lactic acid) is formed. The body must then convert lactate back to glucose for the rest of the cells in the body to utilize as energy. This extra step in metabolism requires additional energy to be expended by the body, which creates a net energy loss and is one reason dogs with cancer develop cachexia.
Protein metabolism is also altered in animals with cancer. The tumor cells produce substances which trigger decreased production of new skeletal muscle, increased breakdown of existing skeletal muscle, and increased liver and whole body protein production, which support tumor growth. This is not only a leading cause of cachexia, but can also lead to decreased immune function, gastrointestinal function, and wound healing. Oncologists believe it is important that protein intake matches protein usage in cancer patients.
Cancer also changes the metabolism of fat. Decreased production of fat and increased catabolism of fat lead to weight loss by depleting the body's fat stores. The tumor cells produce substances which mimic the hormones that control fat metabolism. The tumor also produces substances which decrease the body's ability to use insulin and transport glucose into the rest of the body's cells for energy.
What diet should I feed my pet with cancer?
It is recommended by veterinary oncologists that the diet contains no more than 25% carbohydrates (dry matter content). Low carbohydrate levels will "starve" cancer cells and, in turn, result in lower lactate levels. Less lactate means less energy needs to be spent converting lactate to glucose for energy. Protein levels should exceed the amount found in most adult maintenance diets. Protein should be from a highly digestible source (high quality) and comprise 30 to 45% dry matter content in dog foods and 40 to 50% dry matter in cat foods. This may help alleviate the muscle wasting observed with cachexia in cancer patients.
One study suggested that a low carbohydrate, high protein diet in conjunction with other cancer treatments may reduce metastasis or spread of certain cancers. Diets that are relatively high in fat are thought to starve the tumor cells, as some cancers have difficulty using fat as an energy source. Diets high in fat may pose other health concerns in dogs though, such as pancreatitis. Specific recommendations for fat levels are not outlined, but most commercial maintenance diets are relatively low in their fat content (7-25% dry matter basis).
The addition of Omega-3 fatty acids (Eicosapentaenoic Acid [EPA], Docosahexaenoic Acid [DHA]) to the diet has also been recommended by some veterinary specialists. Animal studies have shown that Omega-3 fatty acids may help preserve fat stores in the body by inhibiting fat catabolism and help decrease muscle (protein) loss. This can reduce the amount of weight loss associated with cachexia and may lead to increased survival time and quality of life in animals with cancer.
As with any medical condition, we recommend discussing your pet's nutritional and dietary needs with your veterinarian. Your veterinarian knows your pet's unique needs and full medical history. But the evidence is quite convincing that the food we feed our pets can vastly influence how the body responds to cancer and can potentially give us more quality time with our beloved four-legged friends.
Ho VW, et al. Carcinogenesis. 2014 Jul 14. Pii: bgu 147 [epub ahead of print] A low carbohydrate, high protein diet combined with celecoxib markedly reduces metastasis.
Roudebush P, et al. Vet Clin Small Anim 2004; 34: 249-269.
Roudebush P. ACVIM Proceedings 2005; The Use of Nutraceuticals in Cancer Therapy.