Small intestinal bacterial overgrowth (SIBO) is a condition where excess bacteria is found in the small intestine, as well an imbalance in the types of bacteria that are present. This can be due to an overgrowth of bacteria in the small intestine, or bacteria moving to the small intestine from the large intestine. 

This leads to gut symptoms such as:

• bloating

• stomach cramps and pain

• excessive wind and belching

• indigestion/reflux

• nausea

• weight loss

• diarrhoea

• constipation

• nutrient malabsorption

The risk of SIBO has been seen to increase when changes to gut have occurred, including gut surgery, or changes to stomach acid, digestive enzymes, or the structure or movement of the gut (1). A 38% higher risk of SIBO has been found in those with IBS, there is also a significant overlap in the symptoms that can occur in both conditions (2, 3). 

How is SIBO diagnosed?

Diagnosing SIBO can be difficult. The ‘gold standard’ diagnosis method involves taking a sample of fluid (an aspirate) from the small intestine and measuring the concentration of bacteria. But as this is quite invasive, it isn’t commonly used in practice (1). 

Breath tests are more commonly used as these are less invasive and more convenient. This works by measuring the levels of gases like hydrogen and methane in the breath in response to consuming glucose or lactulose, as the bacteria will produce these gases if present. But there can be issues with the accuracy of these breath tests, with the risk of both false negatives and false positives (1).  

Doctors also use other information when diagnosing SIBO, including presenting symptoms, relevant blood test results and failure to respond to other gut-related treatments (4). 

Currently, the most common treatment option for SIBO is a course of antibiotics like Rifaximin, Neomycin or Vancomycin – sometimes used in rotation (4). 

 This has been seen to resolve SIBO in 51.5% of those diagnosed with SIBO from a breath test (5).  

Can diet play a role?

There is no good evidence that dietary changes can treat SIBO, but certain changes can help to improve symptoms, at least in the short term. 

The low FODMAP diet

The low FODMAP diet is an evidence-based approach that can be used for the treatment of IBS. This involves limiting certain types of carbohydrate that can be fermented by gut bacteria which can then trigger gut symptoms for some people. 

It is thought that this diet could be useful in SIBO management by depriving gut bacteria of nutrition, but most of the evidence is related to the low FODMAP diet is about IBS rather than SIBO (1). As there is a significant overlap between IBS and SIBO, a low FODMAP diet may also be beneficial for those who have both SIBO and IBS. 

Similarly, if lactose intolerance is present alongside SIBO, an ongoing lactose-free diet is needed as well as SIBO treatment (1). 

Important: The low FODMAP diet is a short-term approach that should only be done under the supervision of a Dietitian who has been trained in this approach. 

An elemental diet

An elemental diet involves consuming nutritionally-complete liquid meal replacements that contain nutrients in their most broken down, or readily absorbed state. 

One study of a 2-week elemental diet found 80% resolution of breath test results (6). 

However, elemental diets aren’t commonly used for SIBO as there is limited evidence for this overall, and this is a very restrictive and expensive approach that requires support from a specialised dietitian.

Prebiotics & probiotics

There is mixed evidence about probiotics and SIBO. 

An animal study from 2001 found that probiotics might have a positive impact on movement in the gut (7). And a more recent meta-analysis found that supplementing with probiotics might help in the treatment of SIBO and in reducing stomach pain (8). However, probiotics were not found to help in preventing SIBO and the studies were mainly small and low quality (8). 

But a few studies have found the use of probiotics to be linked with an increased risk of testing positive for SIBO on a methane breath test (9, 10). A study from 2018 also found that stopping probiotics, along with antibiotic treatment, resolved SIBO symptoms (11).  

In a guideline form 2020, the American College of Gastroenterology (ACG) stated “there is a lack of consistent data to support recommending specific probiotics in the treatment of SIBO” (12). 

There’s less evidence related to prebiotics and SIBO, and some prebiotics are high in FODMAPs which could possibly worsen SIBO symptoms. 

A study from 2013 found that supplementing with fructo-oligosaccharide prebiotics after a week-long course of Rifaximin lead to an improvement in a number of SIBO symptoms, with the exception of nausea and number of bowel movements (13). This study also found more improvements from using a probiotic supplement (lactobacillus casei) following Rifaminine. However, the ACG advises that “prebiotics such as inulin should also be avoided ” (12).

Ongoing high-quality research is needed to investigate the impact of prebiotics and probiotics on SIBO. 

Other dietary approaches

Higher fibre diets, like vegan and vegetarian diets may also help with SIBO by rebalancing the gut microbiome and reducing levels of SIBO-related bacteria like E.coli (14). 

Although not backed by evidence specific to SIBO, there’s a theory that anti-inflammatory foods might aid the repair of the gut-lining following SIBO treatment. So including foods like oily fish, olive oil and colourful fruit and vegetables may be helpful — and these foods are nutritious and good for us regardless of SIBO. 

Malabsorption

Malabsorption can also occur as a result of SIBO. At risk nutrients include vitamin B12 and iron (15). Due to disruption of bile acids, fats and fat-soluble vitamins (A, D, E and K) can also be malabsorbed (15). 

Therefore, nutritional treatment may be needed to aid nutrient absorption and to optimise nutritional status once symptoms have resolved. 

Summary

SIBO can lead to very unpleasant symptoms that can have a big impact on quality of life. This condition can also be difficult to diagnose, and treatment can take some time and tweaking. 

Although dietary changes don’t treat SIBO, certain changes can help with managing symptoms and possible issues with malabsorption. This is why support from a gut-specialist dietitian can be important as part of the treatment of SIBO. 

Please speak to your doctor if you suspect SIBO, as the symptoms of SIBO overlap with other gut-related issues.