A Single-arm, Open-label Clinical Trial to Evaluate the Effect of SMT04 in Irritable Bowel Syndrome (IBS)

Inclusion Criteria: * Male or female, aged from 21 years to 70 years old * Meet the criteria of the Rome-III-definition of IBS with diarrhoea or mixed subtypes, or functional diarrhoea Rome-III-definition: Abdominal pain or abdominal discomfort on minimum of three days per month during the last three months, starting at least six months ago, and a minimum of two of the following criteria: * Improvement of symptoms after defecation * Start of symptoms in association with a change in stool frequency * Start of symptoms in association with a change in stool consistency Subtype of IBS-D which requires more than 25% of the participant's stools to be loose and less than 25% hard and lumpy; subtype of IBS-M which the participant's stools must be both hard and lumpy, as well as loose in consistency at least 25% of the time. Functional diarrhoea: The experience of loose or watery stools without pain occurring in at least 75% of bowel movements for at least three months over the last six months. * Have the latest negative colonoscopy result within five years * Literate and can complete questionnaire * Written informed consent is obtained Exclusion Criteria: * Known inflammatory bowel disease, lactose intolerance or other malabsorption syndromes, celiac disease, diabetes mellitus, thyroid dysfunction, cancer, immunodeficiency, autoimmune diseases, severe hepatic or renal insufficiency, other explainable causes of abdominal pain, diarrhoea or constipation * Known operations involving small intestines and large intestines; or history of appendectomy, hysterectomy, and cholecystectomy in last 6 months. * Known severe mental illnesses; unstable type or dose of psychiatric drugs within the last 3 months that will affect their judgement of study participation. * Evidence of active infection at the time of inclusion * History of use of prebiotics, probiotics, antibiotic therapy or anti-inflammatory drugs within the last 2 weeks * Known current pregnancy or breast-feeding female