Special diets for canine cancer patients have been in use since the 90's, based on research that spans from the 1940's to present. Proof that they really make a difference is lacking, but I do tend to use them because many dogs show general improvements in health and over attitude - at least when homemade versions are used.
Tumors take up large amounts of glucose, and they can metabolize it only via anaerobic glycolysis. The end result of tumor glycolysis is release of lactate into circulation. The patient converts lactate back to glucose via the Cori cycle. Increased lactate negatively effects Cori cycle functioning, resulting in a net loss in energy. Tumors also preferentially metabolize certain amino acids at the expense of the host.
Ultimately the metabolic state of cancer patients resembles that of a Type II diabetic – these patients exhibit glucose intolerance, glucose recycling, increased hepatic glucose production, and insulin resistance. A recent study showed that administration of insulin to human patients with a variety of cancers significantly improved food intake and survival (Lundholm, 2007).
Lactate, resting insulin and glucose levels are elevated in dogs with cancer (Ogilvie, 1994a), and they do not improve after treatment (Ogilvie, 1992). Studies in dogs have shown that those with cancer have different lipid profiles than normal dogs. Dogs with cancer had higher levels of cholesterol, total triglyceride and very low density triglycerides, and treatment normalized only cholesterol levels (Ogilvie, 1994b).
In theory, a diet in low in carbohydrates would help to minimize lactate production and prevent complications of glucose intolerance. Special diets targeted towards ameliorating these metabolic changes have been tested in dogs, though apparently not in humans. A high carbohydrate, low fat diet resulted in elevated lactate and insulin levels in dogs with cancer. A high fat, low carbohydrate diet increases the probability that dogs with lymphoma would go into remission and have longer survival times (Ogilvie 2003), (Tisdale, 1987), although these limited data remain unconvincing to many veterinary nutritionists.
A commercial diet formulated to be low in digestible carbohydrates, high in fat (particularly n-3 PUFA) and moderate in protein is Hill’s N/D for dogs. This was the diet tested to improve outcomes in canine lymphoma. However, that study (Ogilvie 2000) did not test a high carb diet vs a low carb diet - both diets tested were low in digestible carbohydrates.Dietary management using these principles is still controversial, as oncologists note that the majority of dogs and cats die or are euthanized because of their tumors but are not cachectic, suggesting that this state of insulin resistance and hyperlactatemia has little clinical significance. I do recommend low carbohydrate diets, however, based on the fact that dogs and cats have no dietary requirement for carbohydrates and on my positive observations of cancer patients on these diets over the years.
Pet owners often find “grainless” commercial “holistic” diets, but should be made aware that if the food in question is a dry food, it must be processed using some kind of starch, and most of these foods contain potato or tapioca. These are starch sources and should perhaps be avoided if possible. The other difference between the commercial low carbohydrate diets and N/D is that the omega-3 levels are not nearly as high nor the proportion of n-3:n-6 fatty acids controlled.
I really prefer homemade food if we are going to change a cancer patient's diet. One of the problems with any of the commercial diets is their very high fat contents. Meat comes with fat, ya know. Homemade diets can be formulated for an individual's specific tastes, medical history and body condition score. Take a fat dog with a history of pancreatitis, for instance - the commercial diets are simply not an option. Not only can we manipulate the fat content, we can change the ingredients to address patient preferences, especially as they may change due to chemo-induced nausea.
My recipes always include veggies and some fruits as well. Plant-derived flavonoids have been studied in the prevention of cancer. These include resveratrol from red grapes (and wine), green tea polyphenols, and phytoestrogens from soy and other plants. Other less well known flavonoids commonly found in medicinal herbs include curcumin (from turmeric), apigenin, anthocyanidins (from berries), quercetin, and many others (approximately 4000 flavonoids have been described). In addition to well-recognized antioxidant effects that may help in prevention of cancer, certain flavonoids have been found to have activity in inducing differentiation and apoptosis, inhibiting protein kinases, facilitating cell-cell communication, inhibiting angiogenesis, cancer cell invasion mechanisms and metastasis mechanisms, as well as enhancing immune function (Boik 2002), (Lopez-Lazaro 2002).
I know, that was a lot of details.