Branched-chain amino acid infusions can decrease protein catabolism in cancer patients. Whether this alter clinical outcomes is yet to be defined. Glutamine is a nonessential amino acid important for gastrointestinal mucosal growth that is often depleted in cancer patients. Because of its instability in simple amino acid form, it is not routinely added to TPN. Surgical patients have improved nitrogen balance, improved protein synthesis, and improved T-lymphocyte response when glutamine is repleted in addition to TPN therapy. Whether this will aid the cancer population requires further study.

The reason standard TPN fails to improve clinical outcomes is that standard TPN does not affect the changes in intermediary metabolism. The addition of metabolic agents or other biological response modifiers to TPN offers promise. Use of insulin improves protein balance in both cachectic animal and human studies. Growth hormone improves protein metabolism, wound healing, and immunologic status in surgical patients. Marrow stimulants can counteract toxic effects of chemotherapeutic agents. Further research is needed in these areas.

Several studies have demonstrated a marked reduction in complications and mortality of severely malnourished patients if given 7-10 days of preoperative nutrional support. These patients have improved serum proteins and immunocompetence. But still, the most common use of nutritional support is postoperative. Nutritional support should begin immediately postoperative if the patient is either severely malnourished or not expected to have oral intake for 5-7 days. A number of studies support this. The question of whether to use TPN or total enteral nutrition (TEN) has yet to be answered conclusively. Enteral nutrition is better on general principles, but most of the abdominal cancer operations interfere with the patient’s tolerance for enteral nutrition. Early nutritional support can be carried out through surgical jejunostomy but this has not yet become common practice in surgical oncology.

Just as in other therapies for cancer, malnourished patients undergoing radiation therapy have increase morbidity and mortality. Radiation therapy can contribute directly to the malnutrition. The effect on the severity of malnutrition and amount of weight loss id dependent on the radiation dose, duration, volume of therapy, and body site being irradiated. Nutritional alterations may be site specific to local therapy. Example of this are nausea and vomiting caused by central nervous system irradiation, and enteritis and malabsorption caused by abdominal irradiation. These acute effects usually improve but may cause the dose of radiation to be limited which, in turn, leads to poorer response rates. As with chemotherapy, there is no evidence that provision of nutritional support to patients receiving radiotheraphy can influence the end result.

   Severely malnourished patients have a diminished response to chemotherapy. These patients have difficulty completing the chemotherapy regime, being more likely to have hematopoietic side effects. Chemotherapy contributes to host malnutrition. Cancer drugs tend to be toxic and produce nausea, vomiting, mucositis, and gastrointestinal dysfunction. These side effects, in the already malnourished cancer patients, will actually influence the outcome of chemotherapy, by causing increased treatment morbidity and mortality.
There is little proof, however, that providing nutritional support to the patient undergoing chemotherapy will improve results, although it will increase the  tolerance to chemotherapy and lower the impact of toxic side effects. A number of explanations have been offered for this, of which the most appealing is that the nutritional support feeds the tumor and helps the tumor survive the chemotherapy. But there is no clinical evidence that this is true.

It is well established that cancer patients with severe malnutrition have worse surgical outcomes than patients who are adequately nourished. They have a higher rate of mortality, a higher rate of major complications, and more infectious complications. These complications include impaired wound healing, anastomotic leaks, abscess formations, infections, fistulas, and postoperative pneumonia. Malnourished cancer patients have impaired immunocompetence. Surgical therapy will further deplete the malnourished cancer patient. The stress response following surgery taxes depleted energy reserves. The patient is often unable to eat for several days after an operation, which further reduces energy reserves. A large cooperative study has demonstrated that in patients with severe malnutrition who must be operated on for cancer, use of perioperative total parenteral nutrition (TPN) can decrease complications and reduce mortality.

Protein calorie malnutrition may diminish tumor growth. Animal studies show significant reduction in tumor growth rates during protein calorie restriction. There have been no human studies to confirm this.