Digestion and absorption of food occurs in the small intestine.  There are usually very few bacteria here, in comparison with the large intestine, where bacteria are needed to continue digestion of food.  SIBO, or bacterial overgrowth, happens when naturally occurring bacteria grow out of control, or when bacteria move from the large intestine to the small intestine. 

Symptoms of SIBO

Signs and symptoms vary, are non-specific and are similar to other conditions and food intolerances.  They can include:-

  • Abdominal pain or discomfort
  • Excessive gas and flatulence
  • Belching
  • Bloating
  • Indigestion
  • Diarrhoea
  • Constipation
  • Malabsorption which can cause anaemia, iron, ferritin and B12 deficiencies
  • An inability to tolerate high fibre foods including onions, garlic, vegetables, beans and lentils
  • Fatigue

Conditions linked to SIBO

  • Irritable Bowel Syndrome
  • Coeliac disease – you should consider being tested for SIBO if you suspect you have coeliac disease but have not responded to a gluten free diet. 
  • Crohn’s disease

Causes of SIBO

Low levels of stomach acid.  This can be caused by:-

  • Natural ageing
  • Helicobacter pylori bacterial infection
  • Medications such as proton pump inhibitors (e.g. Omeprazole).

Motility problems

Food is moved through our gastrointestinal tract by a complicated series of events.  Any problems with this can allow bacteria to grow in the small intestine. 

Motility problems can be caused by surgery, for example, after appendicitis or cancer. 

Stress can reduce the motility of the small intestine. 

Pancreatic insufficiency  – we need pancreatic enzymes to break down food.  Conditions that affect the pancreas, such as diabetes or coeliac disease, might therefore cause SIBO.

Testing for SIBO

At the moment, testing in the NHS is not always available, and a referral to a gastroenterology consultant is required.  The gold standard test involves endoscopy to collect and analyse a sample of small intestinal fluid.  This is invasive and comes with risks. 

At the ROC clinic we offer a fast, comprehensive stool assessment which can lead to a diagnosis of SIBO, as well as treatment for it. 

Difficulties with other tests for SIBO

Alternative tests include the Hydrogen Breath Test (also called a lactulose or glucose breath test). If a large amount of bacteria is present in the small intestine they will produce hydrogen and methane gases which enter the blood and are breathed out by the lungs.  A third gas, Hydrogen Sulphide has also been linked with SIBO, however, standard tests do not detect this. 

This breath tests require a low-fibre diet and fasting for 14 hours. A solution of Lactulose or Glucose is then drank and breath samples are taken at 20 minute intervals for 3 hours.  Using glucose can produce false negative results. Lactulose is better because it moves through the entire small intestine, therefore can detect bacterial grown in the last part of the intestine.  However, false positives can occur.  This is more likely to happen in patients who have frequent diarrhoea. 

We can offer a full history and examination (or video consultation if you prefer) and provide a different testing kit that is done at home with a comprehensive report leading to diagnosis, as well as an individual management plan.  We use the GENOVA test to send stool samples you collect at home to a lab where cutting edge technology is used to reveal detailed information about the cause of many common gastrointestinal symptoms. 

The results show any areas of :-

  • Dysbiosis, which is an imbalance in the gut microflora (your own essential and non-essential bacteria);
  • Inflammation – the test measures any occult (hidden) blood as well as markers of infection or irritation;
  • Maldigestion – the test looks at pancreatic function and products of food breakdown
  • Metabolite imbalance;
  • Infection with bacteria, yeasts or parasites. 

The detailed report you are provided with allows us to determine a short and long term plan to maximise gut health with medications, supplements or lifestyle changes. 

We advise bringing a diary of symptoms and signs including a typical diet to your first consultation. 

Treatment for SIBO

This will vary depending on your lab results.  However, studies have shown that the most successful treatments include:- 


A short course of antibiotics such as Rifaximin can often treat SIBO.  This is currently unavailable on the NHS but we have a supply of this available in the clinic.  


Bacteria feed on carbohydrate, so reducing carbohydrates and sugar alcohols is often recommended.  Problems with a low carbohydrate diet include loss of healthy bacteria or low calcium, so a probiotic supplement is usually suggested. 


Prokinetics promote movement without having a laxative effect.  They include ginger root or medicines such as Prucalopride. 

There is a risk of relapse of SIBO.  This is why it is unlikely you will be offered just one treatment – it is more common to suggest dietary changes, supplements and/or probiotics as well as standard antibiotic regimes.  

If you suspect that food intolerances might be the cause of your symptoms, we can offer the ALEX blood test, which can identify 300 different food or environmental allergens that might also be the cause of your symptoms. 

We look forward to meeting you soon and helping you on your journey to improve gut health


Poon, D. & Andreyev, J.  (2020) Management of difficult to treat small intestinal bacterial overgrowth.  The British Society of Gastroenterology

Takakura, W & Pimentel, M. (2020) Small intestinal bacterial overgrowth and irritable bowel syndrome – an update.  Front Psychiatry; 11: 664

Dukowicz, A C. et al (2007) Small intestinal bacterial overgrowth.  A comprehensive review.  Gastroenterol Hepatol (NY) Feb 3 (2): 112-122

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