Cancer has been shown to result in decreased body muscle mass, skeletal protein synthesis, and alter nitrogen balance while concurrently increasing skeletal protein breakdown, liver protein synthesis, and whole body protein synthesis. 16-18 Tumors preferentially use protein for energy at the expense of the host. 16-18,21-25 Tumors preferentially utilize certain amino acids for gluconeogenesis, which results in abnormal amino acid profiles. These abnormal profiles have been documented in pet animals with a wide variety of cancers. The use of amino acids by the tumor for energy becomes clinically significant for the host when protein degradation and loss exceed synthesis. This can result in alterations in many important bodily functions such as immune response, gastrointestinal function and surgical healing.22,23
Knowledge that cancer preferentially utilizes amino acids and that some amino acids may be therapeutic may be of value when designing a diet for the cancer patient. Providing high quality amino acids or protein in the diet may be of critical importance for the veterinary cancer patient. A quality protein diet that is highly bioavailable may be ideal. Arginine, glycine, cystine and glutamine may be of specific value for therapeutic purposes.26-29 Arginine may stimulate lymphocyte blastogenesis. The addition of arginine to total parenteral nutrition solutions has been shown to decrease tumor growth and metastatic rate in some rodent systems.26,27 Some amino acids my decrease toxicity associated with chemotherapy. For example, glycine has been shown to reduce cisplatin-induced nephrotoxicity.. Cystine has been shown to be effective for reducing Heinz body anemia in cats. Glutamine has been shown to be effective for reducing histologic and clinical evidence of methotrexate-induced gastrointestinal toxicity in cats.
The bottom line is that a diet that has moderate amounts of highly bioavailable protein may be of value to the cancer patient. Certain amino acids such as glutamine, cystine, and arginine may also be beneficial for some cancer patients.32,33