Inclusion Criteria:
1. Aged 18-65 years old at the inclusion of the study, both female and male subjects.
2. Signed Informed Consent; willing and able to comply with study procedures.
3. Willing to maintain their diet and physical activity levels during the study.
4. Able to swallow a size-00 capsule (23mm length and 9mm width).
5. Participants with at least one of the following Rome IV diagnoses: FABD, functional diarrhea, IBS-M, or IBS-D.
6. Baseline weekly average of worst daily (in past 24 hours) abdominal bloating/distension score of \>= 3.0 on a 0-to-10-point scale.
7. Participants with abnormal LHBT following the North American Consensus recommendations (A rise in hydrogen of ≥20 ppm by 90 min).
Exclusion Criteria:
1. History of less than three (3) bowel movements per week.
2. With the diagnosis of IBS-C.
3. Prior gastrointestinal disease, surgery, or abdominal or pelvic radiation treatment which, in the Investigator's opinion, would lead to intestinal structuring or obstruction with a risk of capsule non-excretion, including, e.g., achalasia, eosinophilic esophagitis, any IBD, or previous esophageal, gastric, small intestinal, or colonic surgery. Appendectomy or cholecystectomy more than 3 months before the screening visit is acceptable.
4. Persons with central venous catheters.
5. History of known structural gastrointestinal abnormalities such as structures or fistulas leading to mechanical obstruction.
6. Known history abdominal radiation treatment.
7. Use of any medications in the week prior to the screening study visit, unless part of regular treatment, that could substantially alter gastrointestinal motor function (e.g., opioids, anticholinergics, or GLP-1 analogues); laxative use is allowed if used less than 3 times a week and it is willing to keep unchanged in the week prior to the SIMBA capsule ingestions. Proton pump inhibitors (PPIs) are allowed provided a wash-out period of 48 hours is respected before swallowing the SIMBA capsules and PPI treatment is resumed only 4 hours thereafter.
o Prokinetic use. Potential participants who are not using prokinetics to treat SIBO may be eligible after a 2-week washout period, and willing to not use prokinetics for the study duration.
8. Unable to stop using laxatives or prokinetic medications for 4 days before the study procedure (BT). Laxatives can be resumed after the test is conducted.
9. Organic motility disorder, including gastroparesis, intestinal pseudo-obstruction, systemic sclerosis, Ogilvie's syndrome.
10. Celiac disease (treated or untreated).
11. Any significant heart, liver, lung, kidney, blood, endocrine or nervous system disease, which in the opinion of the investigator, would adversely affect study safety or outcome.
12. Cancer diagnosis or treatment within the past year (non-melanoma skin cancers are acceptable).
13. Gastrointestinal inflammatory diseases, including ulcerative colitis, Crohn's disease, microscopic colitis.
14. Participants with IBS presenting with alarm symptoms such as: rectal bleeding, unexplained weight loss, iron deficiency anemia, and nocturnal symptoms,
15. Participants over the age of 50 or older who have not had:
* a colon cancer screening by either a negative FIT or FOBT test within the last 2 years; OR
* a colonoscopy in the prior 10 years which was negative for colorectal cancer
16. Epilepsy diagnosis.
17. History or diagnosis of immunological diseases, infectious diseases or immune-compromised conditions, which in the opinion of the investigator, would adversely affect study safety or outcome. Such as, but not limited to, hepatitis, tuberculosis, HIV positive, Parkinson's, multiple sclerosis, AIDS, lymphoma, and long-term corticosteroid treatment.
18. History of oropharyngeal dysphagia, or other swallowing disorder with a risk of capsule aspiration.
19. Antibiotic use (except for topical use) ≤ 12 weeks prior to screening. Potential participants may be eligible once a 12-week washout is completed.
20. Regular use of probiotics, prebiotics or synbiotics (including food and drinks containing added probiotics and/or probiotic yogurts with live, active cultures) within 1 month prior to screening. Potential participants may be eligible once a 1-month washout is completed.
21. Any prior Fecal Microbiota Transplantation.
22. Pregnant or breastfeeding.
23. Planning to become pregnant.
24. Alcohol or drug abuse.
25. Allergy to the components present in the probiotic and placebo capsules.
26. Are non-English speaking.
27. Are scheduled for an MRI at any time during the study. Potential participants may be eligible to participate once their MRI procedure is completed.
