Inclusion Criteria:  Diarrhea Predominant Irritable Bowel Syndrome (IBS-D) or Irritable Bowel Syndrome with mixed bowel habits (IBS-M) according to the Rome IV criteria  Exclusion Criteria:  The use of antibiotics within one month prior to faecal microbiota transplantation The use of probiotics within one month prior to faecal microbiota transplantation History of inflammatory bowel disease or gastrointestinal malignancy, systemic autoimmune diseases (ongoing or in history) Previous abdominal surgery (other than appendectomy or cholecystectomy or hernioplasty or cesarean section) HIV infection or other active infection Renal or hepatic disease (both defined by biochemistry workup) Diabetes mellitus, abnormal thyroid functions not controlled by thyroid medications Bipolar disorder or schizophrenia (ongoing or history thereof), moderately severe depression defined by Patient Health Questionnaire-9 (PHQ-9) score > 15 Anxiety defined by a Generalised Anxiety Disorder 7 (GAD7) score > 10 Current pregnancy and lactation