Inclusion Criteria:  Patients who sign informed consent. Borrmann classification of gastric cancer is determined by more than 2 pathologists. Patients with BMI 24-28. Karnofsky (KPS) score >80.  Exclusion Criteria:  Patients who take any aspirin, antibiotics, prebiotics, or probiotics within 4 weeks and steroids or immunosuppressants within 6 months prior to specimen collection. Patients who complicate with other malignant tumors. Patients who complicate with diabetes, hypertension, heart disease and infectious diseases. Patients who complicate with inflammatory bowel disease or irritable bowel syndrome. Patients with metastasis.