Up to date, there has been no RCT which testified whether therapeutic dosage of EPA plus enteral nutrition has combined effects on patients receiving chemotherapy. The investigators choose nutriall as basic nutritional support agent during chemotherapy, and give patients different dosage of EPA. Nutritional and immunologic status, quality of life and side effects of chemotherapy are recorded to evaluate whether EPA can improve outcome of these patients. Through this study the investigators may also optimize the dose of EPA for patients receiving chemotherapy on gastric/colorectal cancer.