Fast growing cancer cells preferentially burn glucose to supply cellular needs. It is believed that cancer cells lack the biological pathways found in normal cells that use fats as an energy source. Theoretically a low carbohydrate diet should starve the fast growing cancer cells. Early research has been encouraging, especially for lymphoma.
This led to the development of a commercial veterinary cancer diet that provides only 14 percent of the total diet metabolic energy (ME) in the form of carbohydrate. This is significantly lower than the almost 50 percent ME from carbohydrates in most commercial foods.
One might think if less is good, than none is better, especially since carnivores have no absolute need for carbohydrates. Biologically, that is not exactly the case. The heart and brain cells of mammals are much like cancer cells. They preferentially use glucose for energy. This is why very low blood sugar can lead to weakness and seizures. In the absence of carbohydrate the liver will burn fat to produce glucose from the amino acids in proteins by a process called gluconeogenesis, or "new sugar." This process requires the destruction of muscle tissue, which turns out to be a problem for the cancer patient.
Cancer patients, especially cats, tend to experience weight loss as their disease progresses prior to diagnosis. Much of the weight loss is a result of muscle loss. This is probably due to the competition between normal cells and cancer cells for sugar, resulting in an increased gluconeogenesis. Also, these animal are older and in various stages of geriatric sarcopenia (decreased muscle mass due to aging). High protein diets help offset these losses and keep the patients in a positive nitrogen state (derived from the fact that all amino acids contain nitrogen molecules).
There is growing evidence that the amino acids glutamine and arginine are of particular benefit to the cancer patient. Glutamine is readily used for energy in many cell types. It also serves as a reservoir for carbon and nitrogen for intracellular metabolism. It has been shown to accelerate healing after radiation therapy and to protect intestinal immunity and integrity following radiation and chemotherapy. Arginine is particularly important in immune system activity and increases antitumor immune responses. Cancer diets with 27-30 percent ME protein levels and enhanced sources of glutamine and arginine have proven beneficial to cancer patients.
With 60-65 percent of ME coming from fat in cancer diets, they provide a rich source of energy that cannot be used by cancer cells. Higher fat diets are also more palatable to dogs and cats and can improve the appetite in these patients.
Increased levels of omega-3 fatty acids have also been shown to provide additional advantages. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) modifies the inflammatory response of the immune system to cancer activity, reducing tissue damage by decreasing certain inflammatory molecules. In addition, EPA and DHA decrease muscle and weight loss in cancer patients.
Much more research is needed to confirm the value of low carbohydrate diets, high protein, and high fat diets in pet cancer patients. So far the research is encouraging and the use of these diets is increasing. Greater usage will help evaluate their efficacy and direct future research needs.
Note: ME percentages are not found on pet food labels and differ from the percentages that are commonly found. It is a more transparent method of judging pet food but is not embraced by the pet food industry. A calculator for converting label information to approximate ME can be found here.
Dr. Ken Tudor