Does SIBO Cause IBS? The Definitive Guide To Understanding IBS & SIBO

Does SIBO Cause IBS? The Definitive Guide To Understanding IBS & SIBO

As you probably bahis know, SIBO is an abbreviation for a digestive condition called small intestinal bacterial overgrowth. It is now being analyzed as a probable cause of irritable bowel syndrome or IBS.

Like other things that are associated with IBS, the problem of small intestinal bacterial overgrowth being the underlying cause is quite complex and marked by controversy as far as IBS research is concerned.

Here, we give you an overview of SIBO and how it relates to IBS. It will help you decide whether you need to consult your doctor about both conditions or not.

What Is SIBO

SIBO is a serious condition of the digestive system, and it occurs when there is a build-up of an excessive amount of bacteria in your small bowel 1.

Any condition that harms the normal motion or transit of your small intestine can make it susceptible to SIBO. Previous abdominal surgery and Crohn’s disease are some of the risk factors associated with the development of small intestinal bacterial overgrowth.

What are the Symptoms of SIBO

Digestive condition

The abnormal number of gut bacteria in your small bowel can cause the following symptoms 2:

How Is SIBO Diagnosed

Assessing the presence of gut bacteria by performing direct biopsies of the small bowel can be difficult. Therefore, a simpler test, commonly called the HBT or hydrogen breath test, is done. The patient is provided a solution, usually, lactulose, to drink. Then, a breath test is performed to look for the presence of hydrogen or methane.

A healthy person would never pass any methane or hydrogen in his breath until 2 hours have passed, which is the estimated time the lactulose takes to reach the large bowel where it would be absorbed by the gut bacteria and release the gas.

A positive result observed within 1 hour 30 minutes of drinking the lactulose provides an indication of bacteria presents higher up in his digestive tract at the level of his small bowel.

sibo breath test


What is IBS

IBS, the acronym for irritable bowel syndrome, is an intestinal disorder. It causes a mix of pain or belly discomfort and a problem with bowel habits, i.e., causing either diarrhea or constipation 3.

It is not a life-threatening disorder, and it does not make you more susceptible to other colon conditions, including Crohn’s disease, ulcerative colitis, or colon cancer.

However, IBS can be an ongoing problem that will have a negative impact on how you live your life. Patients with IBS may frequently miss school or work, and they may feel depressed or bored to take part in their regular activities. Some of them may need to have their work setting altered, i.e., changing their working hours, shifting to working from home, or not working.

What are the Common Symptoms of IBS

small intestine bacterial overgrowth

Patients with IBS are characterized by these common symptoms:

  • Diarrhea (some people can have explosive diarrhea)
  • Abdominal cramps or belly pains, usually occurring in the lower part of the belly. It may get worse after food intake, but gets better after defecation
  • Constipation
  • Bloating or plenty of gas
  • Constipation mixed with diarrhea
  • A belly that stands out
  • Looser or harder stools than normal

SIBO and IBS: What is the Connection

Since bloating is a prevalent symptom among IBS sufferers, irrespective of whether diarrhea or constipation occurs as the main symptom, researchers are now looking for an underlying medical problem.

Furthermore, patients with IBS often indicate specific foods for causing the symptoms, but there is no clear-cut research that can support this view.

The indication that SIBO could be an underlying medical cause for IBS is obtained from two main research findings.

  • The first one shows that remarkably more patients with IBS have been tested positive with HBT than the unaffected people, which possibly indicates that SIBO as an underlying problem 4.
  • The second research finding shows that several IBS patients experience a significant improvement of IBS symptoms after they have been administered specific antibiotics 4. Their stomach does not absorb the given antibiotics, which means they can act on any gut bacteria that are hiding in the small bowel.

This SIBO theory tries to find out why bacteria move up and reaches the wrong place despite the fact that the small bowel has its natural cleansing mechanism, which involves movement of muscles found in the intestinal lining that works to empty the gut consistently.


It is believed that this muscle movement gets impaired, which causes the bacteria to reside in the small intestine. One theory states that a spell of gastroenteritis may cause harm to the muscles that serve for this natural cleansing action, a likelihood that might describe the occurrence of post-infectious IBS. Moreover, stress can decline the cleansing ability of these muscles, which possibly explains the association of stress with IBS.

The theory also attempts to explain that IBS can become evident as either constipation or diarrhea. The reasoning behind this theory is that the various types of bacteria, as well as the gases they produce affect the gut motility in different ways. Research has shown that people who are tested to have a higher volume of methane will likely experience constipation, while those with a higher level of hydrogen are diarrhea predominant.

The SIBO theory also shows that the underlying medical cause for sugar intolerance is SIBO.

The Debate


Although the theory seems to establish the connection between SIBO and IBS in a fine manner, there are many researchers who disagree. Several major criticisms exist of this theory. An important assessment is that the hydrogen breath test (HBT) is not considered a reliable measure because of its high error rate.

Another important fact is that the high rate of occurrence of SIBO and the success rate of antibiotics, as seen in studies conducted by the proponents of the theory, has not always been observed by other researchers. The long-term usage of antibiotics is also a cause for concern because IBS is a chronic intestinal disorder.


As discussed above, the connection between SIBO and IBS is unclear. Most researchers hold the opinion that SIBO may act as the underlying issue for a subset of patients with IBS and that the antibiotic, rifaximin, is effective in reducing symptoms such as bloating and diarrhea.

If you have IBS symptoms, should you speak to your medical practitioner about taking the HBT for SIBO? Since SIBO appears to be an underlying medical issue for some of the IBS patients and an antibiotic has been found to bring symptom relief, it is certainly worth further investigation.

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