SIBO: IBS, symptoms, treatment and diet

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.
 

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.