SIBO (Small Intestinal Bacterial Overgrowth)

Small Intestinal Bacterial Overgrowth (SIBO)

Small Intestinal Bacterial Overgrowth (SIBO) as a diagnosis is very often overlooked and this is particularly the case in patients complaining of reflux symptoms. It is probably far more common than usually perceived and in our view should be considered in all patients thought to have gastro-oesophageal reflux disease. However, it is always important to seek medical advice and to exclude alternative causes for symptoms if necessary.

What is SIBO?

It is normal that literally billions of bacteria and other micro-organisms live in symbiosis with us in the large bowel (colon). However, the small bowel which lies between the stomach and the colon is relatively sterile. It is known that SIBO occurs when the small bowel becomes colonised by abnormal numbers of micro-organisms and these can then cause a variety of symptoms. These tend to ferment carbohydrates, particularly those high in so-called FODMAPs and during this process produce hydrogen gas which can be detected in the breath. The condition can be associated with other diseases which in turn can cause symptoms themselves. It is also likely that SIBO is a specific type of “dysbiosis”; a condition in which the usual balance of micro-organisms in the gut (the gastro-intestinal micro-biome) which is so important for good health is disrupted and that others which we currently are not able to test for almost certainly can cause symptoms and possibly illness.

One of these is now recognised as “Intestinal Methogenic Overgrowth” or IMO. In this dysbiosis rather than bacteria organisms called archaea (Methanobrevibacter smithii) produce excess methane rather than hydrogen gas.

In this short video Mr Nick Boyle, Medical Director at RefluxUK - the UK's largest specialist reflux clinic, talks about SIBO and how it relates to the reflux symptoms patients present with.

What causes SIBO/IMO?

There are thought to be many reasons why SIBO and other dysbiosis develop but the most likely are:

1. Poor gut motility which prevents the normal "clearing" of bacteria. This can be caused by connective tissue conditions such as scleroderma, nervous system disease such as Parkinson's, hypothyroidism and drugs especially opiate pain-killers, but probably most commonly diabetes as this can cause damage to nerves supplying the gut. It is also thought that some viruses may influence motility and this can pre-dispose to the development of dysbiosis; among those implicated is COVID.
2. Low stomach acid. The production of acid by the stomach is a normal physiological phenomenon. Hydrochloric acid starts the process of breaking down the food we eat so that it can be digested. But it also helps to create a barrier, protecting the rest of the gut from the micro-organisms that we inevitably ingest when we swallow and eat. Some of these will be on our food but our mouths and throats are also colonised by many different organisms. Normally these are killed in the stomach but in the absence of normal levels of stomach acid these micro-organisms can pass into the small bowel and then the colon. Low stomach acid can occur following surgery and is also caused by h. Pylori infection. It is associated with pernicious anaemia but the most common cause of profound acid production depression are the powerful anti-acid medications Proton Pump Inhibitors (PPIs). Studies have shown that the usual balance of organisms in the biome is disturbed in patients taking PPIs. Oral bacteria and potentially pathogenic bacteria are increased in the gut microbiota of PPI users and there are more microbial alterations in the gut associated with PPI use than with antibiotics or other drug use. RefluxUK has completed and published a study that showed that nearly two thirds of patients with reflux and symptoms associated with SIBO and taking PPIs long-term tested positive for SIBO. So, these drugs may well be one of the most common causes of a change in the normal gut Biome and the consequences of this. Read more about PPI, their history, efficacy and side effects here.
3. Antibiotics. By their very nature antibiotics will preferentially kill some gut micro-organisms while others will survive therefore disturbing the normal balance within the gut. Used repeatedly, or over the long-term, drug resistance will develop. Sometimes the alteration in the gut biome will precipitate the sudden onset of symptoms but sometimes these may become problematic even years later.
4. Previous surgery. In patients who have undergone gut surgery with for instance removal of the ileo-caecal valve during colon cancer resection.
5. Diverticular disease. It's thought bacteria can "hide" in blind pouches.
6. Abnormal connections between areas of the gut called fistulae.

What symptoms does SIBO cause? What does SIBO feel like?

SIBO and other dysbiosis conditions can cause an enormously wide and variable set of symptoms. It is recognised that SIBO can be associated with Irritable Bowel Syndrome (IBS) in which patients can experience alternating loose stools and sometimes constipation and flatulence associated with abdominal bloating and pain. Indeed, studies suggest that when tested, up to 70% of people with "IBS" will have co-existent SIBO. It is thought that hydrogen producing organisms tend to be associated with diarrhoea while IMO and methane production with constipation. SIBO can cause vitamin especially B12 deficiency and iron deficiency anaemia and malabsorption syndromes possibly due to inflammation of the lining of the gut and poor fat digestion. Some patients complain of “Brain Fog”. In fact SIBO has been associated with more than 100 other conditions including interstitial cystitis, hypothyroidism, fibromyalgia and skin pathology such as rosacea and eczema to name just a few.

SIBO and Reflux

However, it is less well recognised that SIBO can be the cause of acid reflux symptoms. Commonly SIBO causes bloating after eating especially carbohydrates as these are fermented into gases. Sometimes people mistakenly think they may be gluten intolerant. There can be associated abdominal discomfort, particularly in the upper left side, with belching and flatulence as well as “indigestion” type symptoms. These are frequently attributed to “functional dyspepsia” in which no under-lying cause is identified and often treated with PPIs for reflux which can paradoxically exacerbate symptoms.

In our experience SIBO is most frequently associated with Laryngo-Pharyngeal (LPR) symptoms. You can read more about LPR/Silent reflux here. Belching of an aerosol of stomach contents up into the oesophagus and to the throat can cause a sore throat, post-nasal drip, throat clearing, a sensation of a lump in the throat (globus), voice problems as well as others. This aerosol may contain hydrochloric acid as well as the powerful enzyme Pepsin and Bile. However, other reflux symptoms including regurgitation, heartburn and respiratory symptoms can all be associated with intestinal dysbiosis. There is also some evidence that constipation can increase the frequency of so-called Transient Lower Oesophageal Relaxations (TLOSRs) which are associated with acid reflux and so use of laxatives can sometimes help reduce reflux symptoms. Since IMO is associated with constipation this may be another mechanism by which intestinal dysbiosis causes reflux symptoms.

Testing for SIBO

Firstly, it's important to remember that the symptoms caused by SIBO can also be secondary to many other conditions and occasionally potentially serious disease. Most people we see will be aware that their symptoms are long-standing and many will have been investigated previously. Nonetheless if there are any alarm symptoms it is clearly important to exclude serious disease before assuming SIBO is responsible.

The most accurate method how to test for SIBO is to take aspirates from the duodenum (the first part of the small bowel after the stomach) and then culture these to see which bacteria grow. This is invasive and impractical and so we use breath tests. You'll be sent a kit so you can do the test at home. You'll swallow a sugar solution and then breathe into a series of small bottles over two hours. You'll then send the kit back to us and we'll analyse the contents of the bottles to measure hydrogen and methane gases. If you have SIBO and/or IMO in which micro-organisms in the gut metabolise the sugar solution into these gases, their concentration in the exhaled breath will be higher than normal.

It can sometimes be difficult to establish whether Small Intestinal Bacterial Overgrowth is a secondary phenomenon caused by PPIs correctly used to treat true reflux or rather the primary cause of symptoms. Consequently, it is usually necessary to exclude primary gastro-oesophageal reflux disease as part of a collection of tests which assess the anatomy and physiology of the stomach and oesophagus. These may include endoscopy, manometry and reflux studies.

Is SIBO curable?

Treatment can be difficult and even the most effective treatment regimens can fail when looking for a SIBO cure.

We see many people with co-existent reflux and Small Intestinal Bacterial Overgrowth symptoms who are taking PPIs. They may have been prescribed these because of reflux symptoms and then developed SIBO which exacerbates their reflux symptoms. Eradicating SIBO while continuing to take PPIs is unlikely to be effective if the PPIs are its cause and stopping these in the context of significant reflux symptoms can be equally difficult. Many people take PPIs for obscure reasons and often their reflux can be better treated with dietary modification, different drugs or even surgery.

Having eliminated an identifiable and treatable cause of SIBO the main pillars of treatment are dietary modification to deprive the responsible bacteria of their food, antibiotics to destroy the unwanted bacteria and pro-biotics to re-establish a normal gastrointestinal bacterial flora. Sometimes drugs which improve gastro-intestinal motility will also be used in the treatment regime which should be tailored to each patient individually. Currently the evidence is that Rifaxamin will eradicate SIBO in 70% of patients. It is the most effective antibiotic and since its effect is largely confined to the small bowel it has a minimal effect on the colonic micro-biome. For these reasons we would not advise the use of less specific wide-spectrum antibiotics in SIBO therapy. When IMO is diagnosed we usually add a second antibiotic called Neomycin which is especially effective when used with Rifaxamin rather than in isolation.

Ultimately, the key to success is making the right diagnosis and treating each patient as an individual. At RefluxUK we understand how debilitating "functional" gut symptoms including those caused by acid reflux and SIBO can be. We will work with you to agree a tailored approach to diagnose and treat your symptoms, provide you with specialist medical and dietician advice and hopefully achieve the best likelihood of eliminating them.

Page reviewed by: Mr Nick Boyle BM MS FRCS 01/09/24