1. Clinical nutritional support therapy is an important progress of modern medicine.
2. Conventional methods of clinical nutrition assessment (Anthropometric, lab, etc.) not just lack of accuracy and immediacy but also difficult to dynamically reflect the fluctuation trend of nutrition status.
3. It has been reported that malnutrition affects proliferation and apoptosis of human cells in vivo. This preliminary study was initiated by the hypothesis that changes in nutritional status may be reflected rapidly in fast proliferating cells.
4. In the previous studies the investigators already found that apoptosis rate of oral mucosal epithelium could reflect changes in nutritional status.There were an obvious decreasing in apoptosis and proliferation rate of oral mucosal epithelium in malnourished patients.
5. Based on the patient's curve of apoptosis rate of oral mucosal epithelium, the plateau being achieved by increase the nutrition amount continuously, Maintain this amount of nutrition given until the end of treatment. The investigators call this amount of nutrition the "upper limit nutrition support therapy".
6. The patients applying for"upper limit nutrition support therapy" and "Formula nutrition support therapy" separately, comparing of the two methods influences on postoperative wound healing, postoperative complication rate ,inflammatory response, side effects of chemotherapy, hospital stays and hospitalization expenses.

Inclusion Criteria:

1. Patients with Gastric cancer or colorectal cancer which confirmed by Preoperative pathology will be included.
2. Patients who are diagnosed as malnutrition according history, physical examination and Nutrition Risk Screening 2002 will be included.
3. patients who have digestive tract fistula because of operation complication will be included.
4. patients who need fast track recovery after colorectal cancer operation will be included.

Exclusion Criteria:

1. Patients who are diagnosed as Late stage (stage IV) gastric cancer or colorectal cancer and can not accomplish radical resection will be excluded.
2. Postoperative gastric cancer or colorectal cancer patients who is Unable to tolerate the chemotherapy or unable to complete the whole chemotherapy course will be excluded.
3. patients with Severe endocrine system disease such as diabetic mellitus, hyperthyroidism will be excluded.
4. patients with cardiac, renal, respiratory, or hepatic diseases, diabetes,active infection, evidence of sepsis, active bleeding or obstruction, and oral disease will be excluded.