The 10 Most Important Things to Know About IBS and SIBO

Although the role of small intestinal bacterial overgrowth (SIBO) in irritable bowel syndrome (IBS) is still not entirely clear, more and more healthcare providers are diagnosing SIBO in their IBS patients, along with providing a prescription for a course of antibiotics. This article answers the most common questions that IBS patients have about SIBO.

Midsection Of Senior Woman Suffering From Stomachache
Michael Heim / EyeEm / Getty Images

1. What is SIBO?

SIBO is an acronym for small intestinal bacterial overgrowth. In a healthy digestive system, the amount of gut bacteria found within the small intestine is quite low. SIBO is diagnosed when there is an excessive amount of bacteria within the small intestine. SIBO is often the result of some anatomical abnormality or digestive illness. More recently, SIBO has been theorized to be a possible cause of IBS symptoms in some IBS patients.

2. How would I know if my IBS is really SIBO?

Many of the symptoms of SIBO are similar to those of IBS:

  • Abdominal pain
  • Bloating
  • Distension
  • Diarrhea
  • Flatulence

Some SIBO patients also experience diarrhea urgency, fecal incontinence, and/or nausea. Although SIBO is seen more often in patients with IBS-D, SIBO may be seen in patients with IBS-C.

3. How is SIBO diagnosed?

Although there are questions about its validity, most cases of SIBO are diagnosed through the use of hydrogen (or methane) breath testing. You will be asked to drink a sugar solution and then provide samples of your breath at various intervals. If hydrogen or methane is detected within 90 minutes, SIBO will be diagnosed. The length of time is key - since it generally would take two hours for the sugar solution to make its way to the large intestine, any rise in these gases prior to that time suggest that the sugar was acted upon by bacteria within the small intestine. In individuals with SIBO, hydrogen in the breath is more likely to be associated with IBS-D, while methane is more likely to be produced by people with IBS-C.

SIBO can be more definitively diagnosed through the use of a sample culture taken directly from your small intestine through the use of an endoscopy.

4. Should I be tested for SIBO?

You should talk with your healthcare provider regarding the likelihood that you have SIBO and to see if you should undergo breath testing. Some signs that SIBO may be playing a role in your IBS symptoms include:

  • You experience gas and bloating within 90 minutes after eating.
  • Your abdomen gets more distended as your day goes on.
  • You have seen an improvement in your IBS symptoms when you have taken antibiotics in the past.

5. How is SIBO treated?

If your healthcare provider has diagnosed you as having SIBO, the primary form of treatment is the use of a certain type of antibiotic (see, "Antibiotics as a Treatment for IBS"). The type of antibiotic chosen for the treatment of SIBO is one that is not absorbed in the stomach and therefore makes its way to the small intestine where it can eliminate any bacteria it finds there. Although such antibiotics have been shown to be effective, they are not yet approved of by the FDA for use in IBS. It is also important to be aware that SIBO can re-occur even after you have been successfully treated initially.

6. If I have SIBO, does this mean that I don't have IBS?

If you are diagnosed with SIBO, it means that your healthcare provider has likely identified the cause of your IBS symptoms. With successful treatment, you should experience relief from many of your IBS symptoms.

7. How serious is SIBO?

Although in some severe cases, SIBO can lead to serious symptoms related to nutritional deficiencies, this is generally not the case for IBS patients who have SIBO. Typically, SIBO leads to unpleasant and unwanted symptoms but it does not pose a risk to your overall health, nor does it lead to other diseases. SIBO will not shorten your life.

8. If I take antibiotics, will my food sensitivities go away?

Possibly. If SIBO was the cause of your digestive symptoms and not a food sensitivity, then there is a good chance that eradicating the bacteria in the small intestine through the use of antibiotics may allow you to eat some foods that previously were trigger foods for you. On the other hand, it is possible to have a sensitivity to certain foods separate from the action of the bacteria within the small intestine. Once you have completed your course of antibiotics, you could challenge yourself with previously troublesome foods to see what kind of reaction you experience. This advice only relates to a food sensitivity; never challenge a food that is a known food allergy for you.

9. What should I be eating for SIBO?

Surprisingly, there is very little information available as to what one should be eating during antibiotic treatment and beyond. There are some indications that it is best to eat a typical diet, with a decent amount of carbohydrates, during the course of taking the antibiotic so that there are plenty of bacteria available for the antibiotic to act upon. It has also been suggested that following a low-FODMAP diet once the SIBO has been eliminated may help in terms of reducing the risk of reccurence.

An important aspect of the role of diet in SIBO has to do with when to eat. This is because of the role of the small intestine's "cleansing wave," a phenomenon that occurs between meals. As part of the process of healthy digestion, the muscles lining the small intestine, periodically empty the small intestine of its contents. The SIBO theory for IBS suggests that impairment of the cleansing wave accounts for the proliferation of bacteria within the small intestine. This impairment of the function of the cleansing wave has been theorized to either be due to a slowing down of the action of the muscles as a result of psychosocial stress or is a result of damage to the muscles from a bout of gastroenteritis. In order to maximize your recovery from SIBO, it is suggested that you limit yourself to three meals a day, to provide optimal conditions for the natural cleansing wave to function.

10. Can probiotics help SIBO?

The research to date on the use of probiotics for SIBO is limited and has not yet shown a clear-cut benefit. It may be best to avoid taking a probiotic supplement until after you have completed your course of antibiotics. Your healthcare provider is in the best position to advise you as to whether or not you should be taking a probiotic supplement.

5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Bohm M, Siwiec RM, Wo JM. Diagnosis and management of small intestinal bacterial overgrowth. Nutr Clin Pract. 2013;28(3):289-99. doi:10.1177/0884533613485882

  2. Ghoshal UC, Shukla R, Ghoshal U. Small Intestinal Bacterial Overgrowth and Irritable Bowel Syndrome: A Bridge between Functional Organic Dichotomy. Gut Liver. 2017;11(2):196-208. doi:10.5009/gnl16126

  3. Borghini R, Donato G, Alvaro D, Picarelli A. New insights in IBS-like disorders: Pandora's box has been opened; a review. Gastroenterol Hepatol Bed Bench. 2017;10(2):79-89.

  4. Lee KN, Lee OY, Koh DH, et al. Association between symptoms of irritable bowel syndrome and methane and hydrogen on lactulose breath test. J Korean Med Sci. 2013;28(6):901-7.  doi:10.3346/jkms.2013.28.6.901

  5. Barkin JA, Keihanian T, Barkin JS, Antequera CM, Moshiree B. Preferential usage of rifaximin for the treatment of hydrogen-positive smallintestinal bacterial overgrowth. Rev Gastroenterol Peru. 2019;39(2):111-115.

By Barbara Bolen, PhD
Barbara Bolen, PhD, is a licensed clinical psychologist and health coach. She has written multiple books focused on living with irritable bowel syndrome.