This is a prospective, single-blind, randomized parallel study to investigate whether B. subtilis could improve clinical symptoms of IBS-D patients. Patients are randomly assigned by envelope method. A senior gastroenterologist is responsible for prescribing medication. Researchers are blind to patients' medication. Participants with IBS are recruited and randomized to receive a 4-week administration of B. subtilis-based probiotics. Clinical symptoms and stool samples are collected before and after the trial.

Inclusion Criteria:

Patients are diagnosed with IBS. IBS was diagnosed based on the Rome IV criteria. Subjects aged from 16-80 years old without any gut medical conditions like inflammatory bowel diseases, infectious diarrhea, colon tumors were included.

Exclusion Criteria:

Subjects who are taking any probiotics, PPIs, antibiotics or any drugs affecting uric acid levels for at least one month before the study.

Subjects who decline to participate into the study.