Evaluating the Safety and Efficacy of the Probiotic Bifidobacterium Longum ES1 and the Post Biotic Heat-treated Bifidobacterium Longum ES1 (HT-ES1) on IBS Symptom Severity in Patients With Diarrhoea Predominant Irritable Bowel Syndrome

Inclusion Criteria: 1. Males and females aged ≥18 to ≤ 65 years. 2. Participants diagnosed with diarrhoea-predominant irritable bowel syndrome (IBS-D) as per ROME IV criteria: i) Recurrent abdominal pain on average at least one day/week in the last three months, associated with two or more of the following criteria: Related to defecation Associated with a change in stool frequency (increase/decrease in frequency). Associated with a change in the form (appearance) of stool. ii) History of abnormal bowel movements predominantly diarrhoea (\>25% of bowel movement categorised as stool form type 6 or 7 (diarrhoea) and \<25% as stool form type 1 or 2 constipation) on BSFS). 3. Participants with an IBS-SSS score ≥ 175. 4. Participants who test negative for COVID-19 by Rapid Antigen Lateral Flow Test Device. 5. Participants who can comply and perform the procedures as per the protocol (consumption of study medications, biological sample collection procedures, and study visit schedule). Female participants who are willing to use acceptable contraceptives during the study duration. 6. Participants who are literate enough to understand the purpose of the study and their rights. 7. Participants who are able to give written informed consent and are willing to participate in the study. Exclusion Criteria: 1. Participants diagnosed with anxiety as assessed by STAI-AD S- anxiety subscale score ≥ 40. 2. Gluten and/or lactose intolerant individuals. 3. Abnormal Thyroid Stimulating Hormone (TSH) value which is (\< 0.4 to \> 4.2 mIU/L). 4. Participants with uncontrolled type II diabetes mellitus defined as random blood glucose (RBG) \> 199 mg/dL or fasting blood glucose (FBG) \>125 mg/dL. 5. Participants with a body mass index (BMI) ≥ 30 kg/m2. 6. Presence of uncontrolled hypertension defined as systolic blood pressure (SBP) ≥ 140 mm Hg and/or diastolic blood pressure (DBP) ≥ 90 mm Hg. 7. Participants with a history of intake of antibiotics (Rifaximin, metronidazole, or any other), other probiotics, prebiotics, synbiotic, proton pump inhibitors, acid sequestrants (cholestyramine, Bile colestipol), FODMAP diet, and histamine H2- receptor antagonists/H2 blockers within six weeks prior to the screening day. 8. Participants with a history of daily intake of antidepressants (Tricyclic antidepressants, Selective serotonin reuptake inhibitors (SSRIs), and Selective serotonin-norepinephrine reuptake Inhibitors (SSNRIs)), clonidine, otilonium bromide, asimadoline, eluxadoline, diphenoxylate, antispasmodics including mebeverine and pinnaverium and anticholinergics within two weeks before the screening day. 9. Participants with a history of bariatric surgery or surgical resection of the stomach, small intestine, or large intestine. 10. Participants showing signs of bile acid malabsorption (BAM), as evident from the history of green colour or foul odour of the stool during the last month. 11. Participants with a history of or complications from malignant tumours. 12. Participation in other clinical trials in the last 90 days prior to screening 13. Active smokers or using any form of smokeless tobacco. 14. Participants with substance abuse problems (within two years) defined as: 15. Use of recreational drugs (such as cocaine, methamphetamine, marijuana, etc.)/Nicotine dependence. 16. High-risk drinking as defined by the consumption of four or more alcohol-containing beverages on any day or eight or more alcohol- containing beverages per week for women and five or more alcohol-containing beverages on any day or 15 or more alcohol- containing beverages per week for men. 17. Participants having clinically significant illnesses of cardiovascular, endocrine, immune, respiratory, hepato-biliary, kidney and urinary, haematological, musculoskeletal system and/or any inflammatory disorder, tumour, and other gastrointestinal diseases.