Small Intestinal Bacterial Overgrowth

Small Intestinal Bacterial Overgrowth (SIBO)

Small Intestinal Bacterial Overgrowth (SIBO) or blind loop syndrome occurs when there is an increase in the overall bacterial population in the small intestine. It’s particularly common when types of bacteria not usually found in this part of the intestines are present.

SIBO usually occurs alongside another circumstance, such as surgery or disease, which results in slower passage of food and waste into the digestive tract. This slower movement creates the perfect breeding ground for bacteria.

Symptoms of SIBO

The most common symptoms of SIBO include:

  • Diarrhoea
  • Unexpected or unintentional weight loss
  • Loss of appetite
  • Consistent nausea
  • Bloating and abdominal pain
  • Discomfort and a feeling over over-fullness after meals
  • Malnutritio

Common Causes of SIBO

The most common symptoms of SIBO include:

SIBO can be caused by a number of different occurrences and factors and is most commonly caused by:

Medical conditions: patients with specific conditions and diseases are more prone to SIBO. These include coeliac disease, diabetes, Crohn’s disease, scleroderma and radiation enteritis

Abdominal surgery complications: surgeries such as gastric bypass, gastrectomy can lead SIBO developing at a later date

Small intestinal structure problems: issues such as scar tissue which may wrap around the small intestine or intestinal diverticulosis, where pouches of tissue bulge through the wall of the intestine


Diagnosis of SIBO requires testing to check bacterial overgrowth within the small intestine. The most frequently used methods of diagnosis are:

Breath Testing

A non-invasive test, breath testing measures the amount of methane or hydrogen breathed out after drinking a glucose-water mixture. Rapid rises in hydrogen or methane may be indicative of SIBO. It’s not the most specific method of testing but gives a general picture.

Small Intestine Aspirate ad Fluid Cultures

Through the use of an endoscope, your doctor will take a sample of intestinal fluid from your small intestine and send it to the lab to check bacterial growth.

In addition to these specific tests, blood tests to check for vitamin deficiencies and stool evaluation to measure fat absorption levels can also be helpful.

Treatment for SIBO

When there is an underlying problem, your doctor should seek to repair this to stop the risk of SIBO returning once treated. Once the underlying issue is solved, SIBO is usually treated the antibiotic therapy and a closer examination of nutritional deficiencies.


The most effective way of treating bacterial growth is antibiotics. It may be possible to begin antibiotic therapy before testing and then if not effective, this may be when further examination is required. A short course of antibiotics is usually effective in reducing the abnormal bacteria in the intestine. If the underlying problem is not treated then the bacteria can quickly return and for some patients, long-term antibiotics are prescribed.

Nutritional Support

Nutritional deficiencies may play a key role in treating and manging SIBO. People suffering from malnutrition due to SIBO will need nutritional support and help to reduce intestinal distress as well as boosting their vitamin intake. Treatments include:

  • Nutritional supplementation: patients with SIBO can be offered intramuscular B-12 injections as well as iron and calcium supplements.
  • Lactose-free nutrition: damage within the small intestine can make it hard or impossible for the body to digest lactose (milk sugar) so avoiding lactose-based products is recommended for better gut health.

Overview Of Diagnosis And Management Of Small Intestinal Bacterial Overgrowth

My tips to tackle a common problem by Dr Rehan Haidry

Read full article here

SIBO (small intestinal bacterial overgrowth)

SIBO (small intestinal bacterial overgrowth) is a relapsing and remitting condition that affects up to 10-15% of the general population.  The hallmark of SIBO is that the small intestine becomes colonised with normal occurring gut flora.  The small intestine is normally devoid of any bacterial colonisation but changes in the environment within the small bowel can lead to overgrowth of bacteria which can manifest with a myriad symptoms which are the hallmark of SIBO.

Once a patient develops SIBO they can present with a constellation of symptoms including bloating, abdominal discomfort, gas, diarrhoea and fatigue, amongst many others.  For many years patients with SIBO symptoms have been diagnosed and labelled with irritable bowel syndrome. This is predominantly because there is a lack of consensus and clarity internationally regarding the natural history of the disease, the best modality for diagnosing it but also a lack of robust data on the optimum treatment algorithm for these patients.

The small intestine does not normally have any bacterial colonisation.  In SIBO what happens is that bacteria that normally live within the gastrointestinal tract, predominantly in our large bowel, start to grow within the small bowel.  As a result, these bacteria feed off small molecule fermentable carbohydrates and sugars that we ingest. These are present in almost everything that we eat and the subsequent gas production in SIBO can cause problems with digestion, absorption of food and damaging the membranes in the lining of the small intestine leading to all of the above symptoms.

There are several risk factors that have been identified for SIBO.The most important thing to say is that it can occur in normal individuals, as is often the case in my practice where I see patients who have no previous medical or GI history presenting with the above symptoms in whom we diagnose bacterial overgrowth.  However, other risk factors that have been identified are anatomical abnormalities such as people who have had previous small bowel resection surgery or gastric bypass.  We know that several medications that can slow down the movement in gut motility such as narcotic pain killers and anti-diarrhoeal agents can lead to bacterial overgrowth.  We are now in a position where we often prescribe a lot of acid suppression medication and drugs such as proton pump inhibitors that reduce the amount of acid going into the small bowel. This can also predispose to bacterial overgrowth.   I also see a lot of patients with underlying connective tissue disorders such as fibromyalgia, Ehlers-Danlos syndrome and rheumatoid arthritis who are predisposed to relapsing symptoms of small intestinal bacterial overgrowth.

The diagnosis of bacterial overgrowth still remains an area of controversy with several different modalities being proposed. At The London Gastroenterology Centre we offer a simple and non-invasive way of testing for it by using a simple breath test.  Please contact my team if you would like to arrange a test. It must be noted that there is not a universally-acceptable gold standard test for SIBO and the use of the lactulose breath test has become extremely common over the past five years.  The purpose of this test is to try and replicate an environment within the small bowel that would occur on a day-to-day basis in patients with small intestinal bacterial overgrowth and then measure the production of gasses that are resultantly produced in the small bowel to quantify whether there is indeed SIBO.  Quantification of hydrogen and methane gas in breath samples is the most inexpensive, non-invasive and probably the most widely available test for a diagnosis of bacterial overgrowth within the United Kingdom.  When we measure these gasses in human breath, it signifies the metabolism of fermentable carbohydrates that reside in the small bowel.  It is also very important to gauge the success of any intervention for the treatment of bacterial overgrowth by repeating a breath test weeks later to ensure that there has been not just a resolution in the production of hydrogen and methane following either antibiotics or dietary restriction, but also to understand that the patient’s symptoms have responded.  Certainly in my practice I almost always repeat the breath test six weeks after any intervention to ensure that there has been success.

Interestingly once patients have completed the breath tests I often sit with them and discuss the likelihood of the long term durability of successful treatment but also a number of courses of antibiotics that patients are likely to require to eradicate the SIBBO.  It must be noted that not every patient needs antibiotics, and as you will read later on in this article other modalities can be explored in my practice. From my experience for the average person each course of two weeks of antibiotics results in an average drop of 25-35ppm in gas production.  It would be noted, however, that some people will experience far greater decreases.  Normal gas production in the small intestine in the first 120 minutes of the breath test should be less than 20ppm of hydrogen and less than 12ppm of methane, therefore based on the lactulose breath test that you have at The London Gastroenterology Centre and the magnitude of the gas production we can estimate how many rounds of treatment you are likely to require.


Treatment of SIBO in my practice at The London Gastroenterology Centre comprises three strategies. Firstly is to induce remission of SIBO, secondly is to try and maintain remission and prevent SIBO returning and finally and probably as importantly is to treat or modify the underlying cause or predisposing factors that are leading to the development of SIBO.

The treatment of bacterial overgrowth, although controversial, is still predominantly focussed on trying to decrease the numbers and overgrowth of bacteria in the small bowel and antibiotics remain the mainstay of therapy for now.  It must be stated, however, that the choice, dose and duration of antibiotic therapy are still not fully understood as there have been very limited high-quality studies that guide clinicians on which antibiotic to use.

However, certainly in my practice over the past five years I have focussed on using Rifaximin, which is one of the most extensively-studied antibiotics in patients with all types of functional bowel disorders.  It has some excellent studies from around the world showing it is safe and effective for treating SIBIO. It is particularly effective in those with hydrogen over production and diarrhoea and bloating symptoms. The problem in the United Kingdom is that it is only approved for the use of travellers’ diarrhoea but also in patients with liver disease and therefore its use in small intestinal bacterial overgrowth is often problematic, as many hospitals or GP practices will not prescribe it and patients often have to pay for a two week course of antibiotics.  Nonetheless there have been many studies that have shown that in patients with bacterial overgrowth and hydrogen overproduction that Rifaximin can be efficacious.  Please ask the team at the LGC for more information on how to source Rifaximin in the UK.

It must also be noted that when we carry out breath tests to look for SIBO we also look for methane gas production.  There is good evidence that has been presented recently at Digestive Disease Weekly in Chicago 2017, showing that methane overproduction can lead to slow transit and motility of the gut and these patients often do not respond to Rifaximin alone and need a second antibiotic.  Neomycin is a safe antibiotic that has been used in various other disease states and has been shown to improve methane overproduction in patients.  The use of pro-kinetics in this cohort of patients such as a low dose of a drug called prucalopride can supplement the effect of the antibiotics to stimulate gut motility and enhance the efficacy of the treatment.

In some patients there is also the option of herbal antibiotics and I see a lot of patients at The London Gastroenterology Centre who want to explore this.  We are happy to discuss and guide patients as to which herbal antibiotics to use as long as they are sourced from a reputable chemist. The options are however very limited.

Maintenance of remission is very important as SIBO is a relapsing disorder in several patients.  In some studies up to one-third of patients will have a relapse of small intestinal bacterial overgrowth and watchful observation is mandatory in patients after induction of remission of SIBO to ensure if there are recurring symptoms that early treatment is instigated.  In my practice at The London Gastroenterology Centre I use the following modalities in preventing SIBO from returning and one of the things a patient should look at is firstly diet.  Limiting fermentable carbohydrates and following a diet such as the low FODMAP diet can ensure that the luminal environment is exposed to low fermentable foods and can ensure that there is a less favourable environment for any residual bacteria to overgrow.  Data have shown that in some patients a low FODMAP diet alone can induce remission in patients with bacterial overgrowth. As importantly the movement and motility of the small bowel needs to be optimised by the use of pro-kinetics.  Prokinetics help stimulate the MMC (migrating motor complex) of the small intestine to prevent recurrence and recolonization of bacteria. I always advise patients that as soon as they have finished their first course of antibiotic treatment we can look at prokinetics.  Again these fall into herbal options such as iberogast drops which can be taken at night or pharmacological treatments such as a low dose of Resolor (prucalopride) at night. I also encourage patients to explore the use of digestive and pancreatic enzymes in trying to optimise the small bowel environment after treatment to prevent SIBO from returning.

In some patients in whom the above measures have not been successful one can look at using more rigorous dietetic exclusion such as the elemental diet.  I have to be honest that this is only reserved for patients with really refractory symptoms despite at least tow to three courses of antibiotics and failure of a trial of a low FODMAP diet.  In the simplest description an elemental diet is a diet that consists of a liquid formula that contains pre-digested carbohydrates, proteins and fats and has been used for many years in the treatment of conditions such as Crohn’s disease.  What the elemental diet means is that the above nutrients are absorbed very quickly through the digestive system, which is helpful in patients with bacterial overgrowth as we do not want food sitting around in the small intestine where it can be used to fuel gas production for the unwanted overgrowth of bacteria.  An elemental diet provides a way to nourish the patient whilst starving off the bacteria.  Implementing the elemental diet is almost always done under the supervision of one of our expert dieticians, and the patients will drink a formula instead of their regular meals for up to two to three weeks depending on the severity of their symptoms and their medical background.  It must also be emphasised that there is not a plethora of high-quality studies on the use of the elemental diet but there are some studies that have shown that in some patients following 14 days of the elemental diet there is an 80% response with negative breath test after treatment.  Clearly there are drawbacks with this and the most important one is that of compliance; it can be extremely difficult to limit one’s dietary intake just to liquids for two weeks.  If you would like to discuss the use of the elemental diet then please contact The London Gastroenterology Centre to make an appointment to discuss further. We can then connect you with one of our dieticians

Finally there has been a lot of interest in the role of probiotics and prebiotics over the past decade and I often get asked by patients as to whether these have a role in the treatment of bacterial overgrowth.  The exact role of probiotics in the management of SIBO remains unclear and needs to be clarified. Certainly anecdotally it makes sense that by replacing unwanted bacteria with good bacteria so to speak will have a beneficial effect on patients.  Nonetheless I do advise caution on the use of probiotics after treatment of bacterial overgrowth as it can in some patients make things slightly worse in the short term.

In summary as you can read in the paragraphs above small intestinal bacterial overgrowth is a common and often stubborn disease to treat.  We have moved away from focusing purely on an antibiotic-focussed treatment of these patients and are now able to offer a variety of different  interventions that I am happy to discuss with patients in clinic.



If you would like to make an appointment to be tested for SIBO or discuss management of your SIBO then please contact Dr Haidry’s team here.

Dr Rehan Haidry

Consultant Gastroenterologist


Appointments for SIBO

Dr Rehan Haidry treats many patients with SIBO and gastroenteric infections and disease. If you are experiencing any of the symptoms above you can book an appointment directly at one or Dr Haidry’s clinics or seek a referral from your GP.

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For any enquiries about conditions, tests or treatments, please feel free to call Dr Rehan Haidry’s medical secretary Debra Hyams on:

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