The present study is a randomized, double-blind, placebo-controlled, parallel group clinical study that assesses the effect of postbioc on the complaints of subjects with moderate to severe diarrhoea-predominant irritable bowel syndrome (IBS-D). The trial is also evaluating the potential of postbiotic on anxiety, low mood and stress of the participants, as well as its safety and tolerability.

The intervention duration for all the study participants is 12 weeks (intervention phase). Subsequently, the participants will be invited to return to site for an end of study assessment after 21 days of no intervention (post-intervention phase).

Inclusion Criteria:

1. Men and women from 18 to 55 years old.

2. Individuals diagnosed for IBS within the last two years, and meets Rome-IV criteria for IBS: recurrent abdominal pain on average ≥1 day/week in ≥3 months prior to study (with symptom onset ≥6 months prior to study), associated with ≥2 of the following criteria:

   1. Related to defecation
   2. Associated with a change in frequency of stool
   3. Associated with a change in form (appearance) of stool.

3. Has IBS-D, i.e., more than ¼ (25%) of bowel movements with Bristol stool types 6 or 7 and less than ¼ (25%) of bowel movements with Bristol stool types 1 or 2); in other words, put practically and as per FDA: at least 2 days per week with at least one stool that has a consistency of Type 6 or Type 7 BSS.

4. Has an IBS-SSS of at least 175 points at screening.

5. Individuals either with abdominal pain or discomfort (≥ 6 to ≤ 10 on an 11-point scale).

6. Has had no prior line of conventional intervention for IBS or dietary change in the last 4 weeks before screening (e.g., low FODMAP, soluble fibers, antispasmodics, laxatives, obstipants, serotonin agonist/antagonist) i.e., recently diagnosed individuals

7. Individuals' agreement to comply with study procedures, in particular:

   1. to take IP as recommended,
   2. to avoid the use of other products which may influence the gastrointestinal (GI) complaints, mental symptoms or commensal flora during the study as defined in Section 6.8 Prior and Concomitant Therapy,
   3. to keep the habitual dietary habits, level of physical activity as well as the level of caffeine or nicotine (if any),
   4. to complete the individual's diary and study questionnaires.

8. Women of childbearing potential:

   1. commitment to use contraception methods,
   2. Negative pregnancy testing (beta human chorionic gonadotropin test in urine).

9. Readiness not to participate in another clinical study during this study.

10. Participation is based upon written informed consent by the individual following written and oral information by the investigator regarding nature, purpose, consequences and possible risks of the clinical study.

Exclusion Criteria:

1. Known allergy or hypersensitivity to the components of the investigational product.

2. Smokers

3. Lactose or fructose intolerance.

4. Individuals with uncontrolled hypertension as assessed by systolic blood pressure ≥ to 160 mmHg and diastolic blood pressure ≥ to 100mmHg.

5. History of diverticulitis, intestinal obstruction, stricture, toxic megacolon, GI (gastro-intestinal) perforation, fecal impaction, gastric banding, bariatric surgery, adhesions, ischemic colitis, or impaired intestinal circulation (e.g., aorto-iliac disease) or recent unexplained GI bleeding within 3 months prior to screening.

6. History of malignancy within 3 years before screening (except squamous and basal cell carcinomas and cervical carcinoma in situ).

7. History and/or presence of acute or chronic significant GI disease or digestion/absorption disorders (e.g., inflammatory bowel disease, coeliac disease, Clostridium difficile colitis, pancreatitis, disorders in digestive tract motility, gluten enteropathy, etc.)

8. Major gastric, hepatic, biliary, pancreas or intestinal surgery within the last 6 months prior to screening or planned during the study (appendectomy, hemorrhoidectomy, or polypectomy allowed as long as occurred > 3 months prior to study screening; uncomplicated laparoscopic or open cholecystectomy is allowed if no history of post-operative biliary tract pain and surgery occurred > 3 months prior to screening).

9. Clinically significant findings in colonoscopy within the 3 years prior to study.

10. Family history among first degree relatives of colorectal cancer or inflammatory bowel disease.

11. Individuals diagnosed with psychiatric disease (e.g., bipolar disorder, Schizophrenia) with or without medication in the last three years.

12. Individuals currently on medication for anxiety and/or depression

13. Individual has a history and/or presence of other clinically significant condition/disorder, which per investigator's judgement could interfere with the results of the study or the safety of the participants, e.g.:

    1. thyroid gland disorder
    2. hypertension
    3. diabetes mellitus
    4. eating disorder
    5. immunodeficiency
    6. relevant gynecological or urological disorder
    7. any other relevant serious organ or systemic diseases ( e.g., cardiovascular, respiratory, liver, renal, neurological disease, etc.)

14. Regular medication and/or supplementation within the last month prior to and planned during the study:

    1. antibiotics, probiotics, prebiotics within 4 weeks before enrollment for screening.
    2. medication for IBS complaints, e.g., bile acid binders (cholestyramine), rifaximin, alosetron, lubiprostone, eluxadoline and linaclotide
    3. which could influence gastrointestinal functions (e.g., laxatives, opioids, systemic corticosteroids, anti-cholinergics, anti-diarrheals, proton pump inhibitors, H2-blockers, etc.) as per investigator judgement. Exception: ad hoc use of Macrolits.

15. Regular use of psychopharmaca (e.g., hypnotics / sedative drugs, anxiolytics, antidepressants, neuroleptics, anticonvulsants) within 3 months prior to study or adaptogens (e.g., ginseng, Ashwagandha, satavari, St. John's Wort) within 6 weeks prior to and during the study.

16. Introductions of a specific diet (e.g., low carb, vegan, high fibre, low FODMAP) within last 3 months prior to and during the study.

17. Women of child-bearing potential: pregnancy or nursing.

18. History of or current abuse of drugs, alcohol, tobacco/nicotine or medica tion.

19. Participation in another study during the last 30 days prior to and during the study.

20. Any other reason for exclusion as per investigator's judgment, e.g., insufficient compliance with study procedures.