Inclusion Criteria:  Caucasian males and females; Age from 18 to 70 years, inclusive; Good physical and mental condition assessed based on the patient's history and physical examination; Laboratory test results (blood tests, including blood chemistry and antibody tests; and urinalysis) within the normal limits for the local laboratory or considered clinically insignificant by the study investigator; A voluntarily provided written informed consent; Being available throughout the duration of the study; Patients with IBS diagnosed based on the Rome IV criteria; Patients with any form of IBS of at least moderate severity assessed via the IBS-SSS (score >175).  Exclusion Criteria:  Cardiovascular disorders: uncontrolled hypertension (blood pressure > 170/100 mmHg), cerebrovascular disease; Severe respiratory disorders (asthma, chronic obstructive pulmonary disease) Liver or kidney disease and unexplained blood chemistry abnormalities: serum creatinine of more than twice the upper limit of normal, serum aminotransferease (AST or ALT) levels more than twice the upper limit of normal; Gastrointestinal disorders other than IBS (including gastroenteritis, celiac disease, and bacterial infections or parasitic infestations confirmed either clinically or endoscopically); Endocrine disorders, including diabetes (fasting blood glucose > 11 mmol/L) and serum thyroid stimulating hormone (TSH) levels above normal; Severe neurological conditions, with psychosis; Malignancy; Pregnancy or breastfeeding; Hypersensitivity to soy; Lactose intolerance that may explain the symptoms (i.e. the symptoms resolve or considerably subside in response to a lactose-free diet); The use of gastrointestinal motility stimulants or dietary fiber supplements during the 2 weeks preceding the clinical study; The use of antithrombotic agents; A surgical procedure scheduled during the course of the clinical study; Current probiotic use and refusal to undergo a 3-month washout period; Antibiotic therapy within the previous 3 months; The patients who receive antibiotics during the study will be excluded; Being included in another clinical study within the previous 3 months; History of alcohol or substance abuse.