SIBO with IBS: symptoms, treatment and diet

Written by: Dr Aathavan Loganayagam
Published: | Updated: 16/04/2020
Edited by: Laura Burgess

Small intestinal bacterial overgrowth (SIBO) is gaining more and more attention as a potential cause of gut symptoms in at least a subset (4-78%) of irritable bowel syndrome (IBS) patients. 

The small bowel plays a key role in digesting food and absorbing nutrients. However, if the gut bacteria becomes out of balance there can be an increased number in bacteria in the small intestine, which can lead to unpleasant symptoms that are common in cases of IBS and a leaky gut

Here, leading London gastroenterologist Dr Aathavan Loganayagam looks at SIBO in relation to IBS and how the condition can be managed.

A woman is sat at a dinner table waiting for her food to be served.

What is SIBO and its symptoms?

SIBO is a condition diagnosed when an ‘overgrowth’ of bacteria are present in the small intestine. Typically, the small intestine is resident to only small numbers of bacteria, so when an abnormally high number accumulate, this is thought to lead to IBS-like symptoms such as bloating, abdominal pain and diarrhoea, which may occur soon after eating a meal.

Why is SIBO difficult to diagnose?

The best method to diagnose SIBO is via sampling fluid from the small intestine itself (jejunal aspirate) and growing the bacteria found in this fluid to estimate if a very high number of bacteria are present. Whilst this is the most accurate diagnostic test for SIBO, it is quite invasive, so is rarely used in clinical practice.

Hydrogen breath testing is an alternative, non-invasive method for identifying SIBO that is now popular in clinical practice. Two different types of breath tests for SIBO are available (glucose or lactulose), however, both methods have considerable diagnostic limitations.

Unfortunately, both of these tests lack sensitivity and specificity, meaning that there is a considerable chance of getting a false positive or false-negative result. Additionally, testing centres may use different testing procedures or criteria for a SIBO diagnosis, adding to the confusion.

How should SIBO be treated?

Most studies to date have investigated the use of different antibiotics to treat SIBO with variable results. The most promising antibiotic therapy studied so far seems to be Rifaximin, which is a non-absorbable drug that works predominantly in the gut.

However, more research is required to determine exactly how Rifaximin works, optimal dosing and whether repeated treatment courses are useful for patients with recurring symptoms.

Probiotic formulations have also been studied as a treatment for IBS patients with evidence of SIBO, however, so far only a handful of high-quality studies are available with variable results. Of note, preliminary studies have shown that probiotics may enhance the effectiveness of Rifaximin treatment, suggesting that combination therapy may be useful and is an interesting area for future research.

Is there a special diet to follow to help in suspected cases of SIBO?

A low FODMAP diet is also sometimes recommended following antibiotic treatment for SIBO in order to prevent re-occurrence. This is based on the idea that a low FODMAP diet reduces the consumption of fermentable carbohydrates, essentially helping to ‘starve out’ any excess bacteria that may take up residence in the small intestine.

Unfortunately, studies are not yet available to either confirm or deny this theory. Other dietary therapies have also been proposed, such as the elemental diet, the specific carbohydrate diet and the GAPS diet, however, so far these strategies are only supported by anecdotal evidence or single studies.

In summary…

The SIBO-IBS relationship remains elusive. Further research is required to determine better and more accurate ways to diagnose SIBO and set standards for what is ‘normal’ and ‘abnormal’ when it comes to bacteria in the small intestine (both the number and species present).

Currently, the antibiotic Rifaximin appears to be the most effective treatment for SIBO, however, more high-quality research is needed to determine how best to use this medication.

Dietary therapies for SIBO are only just beginning to be explored and more research is needed before they should be routinely recommended.

If you are concerned that you may suffer from SIBO, you can make an appointment today via Dr Loganayagam’s profile about current testing and treatment options available.

By Dr Aathavan Loganayagam

Dr Aathavan Loganayagam trained in medicine at Guy’s, King's and St. Thomas’ medical schools. He then underwent rigorous structured specialty training in gastroenterology and general internal medicine in the well respected South London training programme.

He then spent two years during postgraduate training as a research and endoscopy fellow at Guy’s and St Thomas’ Hospitals, London. His research was in the fields of pharmacogenetics, inflammatory bowel disease and gastrointestinal malignancy. He has received awards and grants for outstanding research work, including the prestigious NHS Innovation London Award.

Dr Loganayagam has numerous publications in peer reviewed journals on all aspects of gastroenterology. He is actively involved in clinical research. He has particular local expertise in the practice of personalised medicine and the utilisation of novel therapeutic agents in the treatment of complex inflammatory bowel disease. He is currently the lead clinician for endoscopy at Queen Elizabeth Hospital, Woolwich.

Diagnostic and advanced therapeutic endoscopy remains a major part of his clinical expertise, including assessment and treatment of inflammatory bowel disease, strictures, polyps and cancers.

Dr Loganayagam is an approachable doctor who takes pride in his communication skills with patients. He is keen to ensure that patients are fully informed and involved in all aspects of their care.

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