Inclusion Criteria:  Ethnic Chinese; Age, 18 to 65 years old; Patients undergoing heart valve surgery with cardiopulmonary bypass  Exclusion Criteria:  Preoperative Pittsburgh Sleep Quality Index global scores higher than 6 Cognitive difficulties Partial or complete gastrectomy Previous esophageal surgery Previous treated by radiotherapy or surgery Inability to conform to the study's requirements Body mass index exceeding 30 kg/m2 Deprivation of a right to decide by an administrative or juridical entity Ongoing participation or participation in another study <1 month ago Recent (< 3 months prior) use of antibiotics, probiotics, prebiotics, symbiotics, hormonal medication, laxatives, proton pump inhibitors, insulin sensitizers or traditional Chinese medicine