Small Intestinal Bacterial Overgrowth (SIBO) is a medical condition characterised by an excessive or abnormal growth of bacteria species in the small intestine. This is the first part of the intestines after the stomach, which is responsible for digesting and absorbing nutrients.  

Whilst it is normal to have a large number of bacteria in the large intestine, their existence in the small bowel can lead to various digestive issues and symptoms such as bloating, abdominal pain, diarrhoea, constipation and nausea. The types of symptoms you may experience is highly individualised and varied with each person experiencing a different set of symptoms or even none at all.  

What causes SIBO?  

SIBO can result from a variety of underlying factors, including:  

• Low stomach acid –reduced levels of stomach acid can decrease the number of bacteria killed in the stomach, allowing more bacteria to reach the small bowel and start growing there.  

• Delayed gastric emptying –when food stays in the stomach longer, it allows more time for bacteria to ferment these food components, promoting not only bacterial survival and the likelihood of overgrowth but also symptoms such as gas, bloating and abdominal pain.  

• Slow bowel transit –just like the point above, a slower bowel transit allows more opportunity and time for bacteria to feed off food components, enabling them to thrive, grow, and cause uncomfortable symptoms such as gas, bloating and abdominal pain.  

• Dysbiosis –an imbalance in gut bacteria, such as an overgrowth of methane-producing bacteria, can slow down transit, enabling increased fermentation in the small bowel, and ultimately allowing the survival of bacteria in the small bowel.  

• Structural abnormalities in the bowel –certain anatomical conditions, such as a shortened colon or diverticulosis in the small intestine, can increase the risk of SIBO development.  

• Food poisoning –ingesting harmful bacteria through contaminated food not only causes immediate symptoms but can also disrupt the balance of beneficial gut bacteria, creating an environment where harmful bacteria can thrive. Ingestion of these harmful bacteria also introduces them directly into your body where they may stay and start to multiply and grow.  

• Medication - antibiotics can get rid of the ‘good bacteria’ in the small bowel allowing more pathogenic species to proliferate and interfere with normal digestive processes causing symptoms. In addition, strong stomach acid suppressants (like proton pump inhibitors (PPI’s)) can cause dysbiosis and bacterial overgrowth either by increasing the risk of catching gut infections or by allowing bacteria that normally live in the mouth and throat to move lower down into the small intestine.  


How is SIBO diagnosed?  

SIBO is commonly diagnosed using a hydrogen and methane breath test. These tests measure the levels of specific gases (hydrogen and methane) in your breath which are produced via bacterial fermentation. Depending on the rise in hydrogen levels seen during the test, this will determine whether you have SIBO or not. Additionally, this breath test can determine whether you have methanogen overgrowth. This is where you have an overgrowth in archaea which are microorganisms, like bacteria, that produce methane gas rather than hydrogen gas.  In about 10% of people with symptoms they produce more hydrogen sulphide which is the ‘eggy’ smelling gas that makes for more mal-odorous flatulence. This is more associated with diarrhoea and abdominal pain and we can now also test for this gas using a different measurement method.

You can find out more detailed information about the SIBO breath tests we offer in clinic in our blog post here: SIBO vs Intestinal Methanogen Overgrowth Test  

Can SIBO be treated?  

SIBO treatment typically involves either antibiotics or a combination of dietary and medical interventions. The first-line treatment plan typically given to patients with SIBO involves a two-week course of antibiotics, most commonly rifaximin.   

Rifaximin is typically the preferred antibiotic of choice because it specifically works within the small intestine and is therefore able to target the microbes living there. Unlike other antibiotics, rifaximin is not absorbed by the body either, making it a potentially safer option in the sense that it is unlikely to disrupt or affect other bodily processes.   

Rifaximin does not always work to eradicate SIBO, particularly if you have a methane-positive result. In this case, the antibiotics neomycin or metronidazole are beneficial to take alongside rifaximin as they can target the methane-producing archaea.   

It is important to note that SIBO can be a persistent condition and can require multiple rounds of antibiotic treatment in order to achieve long-term eradication. With that said, there are also other treatment methods that you could try in order to tackle SIBO.   

Other treatments to try include:  

• Herbal antimicrobials– such as oregano, berberine and wormwood. Some research has demonstrated promising effects of antimicrobials in eradicating SIBO. Of which, some studies have concluded that they may be as effective as antibiotics. With that said, the research in humans is limited to one study and therefore more research is needed to establish the efficacy of antimicrobials.  

• Probiotics– Saccharomyces boulardii (CNCM I 745) and Bacillus coagulans (Unique IS2) may be useful to supplement alongside antibiotics. This is because research has found that such probiotics increased the likelihood of eradicating SIBO. Probiotics are also useful to protect your microbiome and promote a healthy microbiome composition, replenishing those healthy microbes which may be lost as a result of the antibiotics.   

• Partially hydrolysed guar gum (PHGG)- is a type of soluble dietary fibre which has shown to help SIBO eradication when supplemented alongside antibiotics.   

• Intestinal adsorbents– such as Enterosgel, Silicolgel and Fybocalm/Gelselectan. These products can bind to harmful toxins and gases produced within the gastrointestinal (GI) tract, helping to relieve negative symptoms of SIBO such as bloating and abdominal pain. 
 

Rather than taking supplements, there are also dietary strategies you can try in order to eradicate SIBO. The idea here is that by following a specific diet, you can ‘starve’ the bacteria involved in SIBO from their fuel source so they are no longer able to survive. Such diets include the elemental diet or a diet low in fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAPs).   

While some evidence has shown an efficacy of these diets in reducing SIBO symptoms, most likely due to the minimal amounts of fibre, these methods are not ones we would recommend. This is because both diets are extremely restrictive and if not done alongside the help of a dietician or registered nutritionist, it could lead to nutrient deficiencies. Additionally, both of these options should only be followed for a short period of time as they could also lead to negative effects on your microbiome, causing those healthy gut bacteria to be unable to survive.   

If you think you have SIBO, have been diagnosed with SIBO, or just want to find out a bit more, then click here