I think it is important to understand that you can have SIBO, which is a cause of IBS, but not all SIBO people have IBS and not all IBS people have SIBO. Essentially, IBS is a chronic pain syndrome that is associated with abdominal pain at least once a week. This abdominal pain is, in turn, associated with a change in stool frequency. This means the abdominal pain is coupled with diarrhea and/or constipation, and a change in the frequency of your stool form. Your stool form could be mushy, flaky, or it could be like passing little rabbit pellets. Although not necessarily associated with frequency, these changes can be associated with chronic abdominal pain occurring at least once a week and this has been happening for at least three months. The third criteria is that the pain changes with either passing gas or passing stool.
If you are struggling with abdominal pain, your pain changes from day to day and when you are passing gas or stools, your stool is either very frequent or not very frequent, and the stool changes form, then likely you have IBS.
Now, IBS can be due to SIBO but there are many other causes of IBS. IBS can also be due to things like a gluten sensitivity or undiagnosed celiac disease. IBS can also be due to a nickel allergy and traumatic events.
SIBO is relatively a new term which has lately become more of a buzzword in the health industry. SIBO stands for small intestine bacterial overgrowth. Your small intestine does have some protection mechanism in place preventing too many bacteria from populating the space. These include stomach acid, bile, digestive enzymes and the motility in your bowel. If you have experienced certain events like possibly a foodborne illness or a previous food poisoning bacteria could have been planted in your small bowel. For example, you went on a trip somewhere and you caught a bug. This could result in you picking up certain bacteria (what is referred to as a dysbiosis) in your small bowel. The result is too many bacteria in the small bowel compared to the regular population, and these bacteria are no longer of the beneficial type (gram-positive bacteria) and are more towards a gram-negative bacteria.
When testing for SIBO, we are using tests like a hydrogen breath test or a push enteroscopy which allows us to culture these bacteria. In a few select patients where samples of their bacteria were obtained from their entire bowel via a scope with an endoscopy or a camera, those with SIBO have a different population, different type and amount of bacteria than those people that do not have SIBO or symptoms of SIBO.
Thus, a positive hydrogen breath test, or a positive microbiology aspirate (allowing a direct comparison of the bacteria in the small bowel compared to the regular population), fulfill the criteria for SIBO.
You can have SIBO, bacteria in your small bowel, a positive hydrogen breath test, but not have IBS. You can have bacteria that are giving you diarrhea but not abdominal pain. Since you do not have abdominal pain, you fail to fulfill the criteria for IBS. IBS is first and foremost a pain syndrome, whereas SIBO is a bacterial count problem, which we call dysbiosis – too many bacteria and not of the correct population or the correct distribution.