IBS and SIBO (Small Intestinal Bacteria Overgrowth) – is there a connection?

SIBO, or small intestinal bacterial overgrowth, occurs when there is an overgrowth of bacteria in the small intestine. Is your IBS really SIBO? What is the connection?

Whilst you may have heard, or read into, different ways you can support your intestinal health within the large intestine by eating different foods etc you may not have read much about the effect bacteria levels in our small intestine may have on your gut health.

The truth is the majority of our gut bacteria is found in the large intestine, not the small intestine, which is why we hear more about that. However, more research is pointing the finger at SIBO and it’s connection to IBS. In fact SIBO has been implicated in up to 60-80% of all IBS cases1,2.


So what are the symptoms of SIBO? How do they match IBS?

 Symptoms can include nausea, reflux, abdominal cramping, bloating, flatulence, food intolerances and diarrhoea, the very same symptoms as IBS-D (diarrhoea). If you have constipation, SIBO can also be a factor, however as a result of a different bacteria overgrowth that produces methane, and not hydrogen, and results in a slower bowel transit time.

The bacteria overgrowth results in a fermentation of the food being ingested. This then results in an over-production in gas, and with no-where to go results in on-going bloating, reflux and ultimately, changes in bowel motility.


So what causes SIBO to develop?

As I’ve mentioned already, the majority of our gut bacteria live in the large intestine. SIBO can flourish due to factors that can cause the bacteria to migrate to areas that it shouldn’t, or due to factors that change the gut diversity altogether.

These include:

  • Lack of digestive enzymes and stomach acid – this leads to poor digestion of food, leaving it to ferment. Medicines that lower stomach acid, such as PPI’s will also do this.
  • Poor gut motility – you don’t necessarily need to be constipated for this to be poor
  • Hypothyroidism – resulting in an overall slowing of digestion
  • Autoimmune conditions such as Coeliac disease
  • Diverticulitis
  • Diabetes
  • Physical abnormalities from abdominal surgery
  • Antibiotics, which are known to change the diversity of the gut bacteria
  • Other imbalances in the gut such as yeasts and parasites
  • Food poisoning


 How would you know you have SIBO?

 If you have the symptoms outlined above testing is the only sure way to know if you have SIBO. The test itself is a simple breath test, where by you drink a solution of lactulose and then take a breath sample every 15 minutes over 2-3 hours (for this reason it is recommended to have the test performed in a lab, but if that is not possible it can be done at home). GastroLife is the main lab here in Ireland and you can order directly from them.

Other reasons you may suspect you have SIBO and you do experience the symptoms above, is if you have started to take a probiotic and after the first week you are still experiencing increased bloating and symptoms. This may be an indication, but as I’ve said, testing is the only way to know for sure.


If you do have SIBO, what can be done about it?

 There are many ways you can help support your body to deal with SIBO to reduce symptoms and to prevent a re-occurrence. However, with a positive SIBO result treating it with an antibiotic or an appropriate  anti-microbial herbal supplement, along with dietary changes and supports, is the only way to irradicate it long-term. In studies, the natural herbal supplements have been shown to be as effective as the antibiotic3. Bear in mind, with whatever course of treatment you chose several courses may be required.

Both these routes need to be supported with improving gut function and replenishing the good gut bacteria to avoid a relapse, such as:

  • Supporting and restoring digestion, both by adding in supplements as well as changing eating intervals
  • Restoring regular bowel movements with diet and lifestyle changes,
  • Adding in prokinetic agents to encourage good bowel motility such as Ginger
  • Lowering fermentable carbohydrates in the diet to remove some of the food for the bacteria (this will mainly lower symptoms of bloating)
  • Supporting the immune system so that it can fight future infections
  • Calming down inflammation caused by the overgrowth and promoting healing



The symptoms of IBS and SIBO overlap considerably and it can be very hard to know what is causing what. If you have already ruled out other causes for your IBS and you have tried other dietary measures to no avail, SIBO may be part of the reason and it is worth being tested for it.


If you would like to find out more about SIBO and working with me you can contact me here



  1. Peralta S et al. Small intestine bacterial overgrowth and irritable bowel syndrome-related symptoms: experience with Rifaximin. World J Gastroenterol. 2009 Jun 7;15(21):2628–2631.
  2. Lin HC et al. Small intestinal bacterial overgrowth: a framework for understanding irritable bowel syndrome. JAMA. 2004 Aug 18;292(7):852– 858.
  3. Mullin GE, Chedid V et al. Herbal therapy is equivalent to rifaximin for the treatment of small intestinal bacterial overgrowth. Global Advances in Health & Medicine. 2014 May; 3(3): 16-24. Published online 2014 May 1. Doi: 10.7453/gahmj.2014.019

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