Small Intestinal Bacterial Overgrowth (SIBO): What It Is, How to Test For It

By Matt Brereton-Patel November 17, 2016 November 17th, 2018 Uncategorized

Many clients who attend our Nutritional Therapy & Functional Medicine clinic in Manchester have come to us because of frequent abdominal bloating, diarrhoea, ‘foggy’ brain, headaches, fatigue, abdominal pain and in some cases, constipation - all common symptoms of bacterial overgrowth in the small intestine (1).

Here’s what's often going on; we have a complex, living, community of thousands of different strains of bacteria residing in our gastrointestinal system, more specifically in our colon. In healthy individuals, these bacteria can be living in harmony, supporting our immune system (2), synthesis of nutrients (3), appetite regulation (4), and many, many more functions.  However, when these bacteria move higher up in the intestinal system, to the small intestine, they are often associated with a number of adverse signs and symptoms.

And this is where problems can start.

Small intestinal bacterial overgrowth (SIBO) can cause poor absorption of nutrients (5) and can cause production of high levels of gas as a result of the bacteria reacting with dietary carbohydrates - causing fermentation. It’s this gas that causes the abdominal bloating in SIBO and it can be very uncomfortable.

In the UK, it is estimated that up to 22% of people (6) may be suffering with Irritable Bowel Syndrome (IBS) (although estimates do significantly vary), and the root cause could be SIBO in many cases.


So how can we test for SIBO?

There are some challenges to testing for SIBO accurately, however arguably the best option available to us at the moment is a breath test, measuring levels of the methane and hydrogen gases that are produced by the bacteria.

A sugar solutiScreen Shot 2016-11-17 at 16.14.45on (lactulose or glucose) is taken orally after an overnight fast. Preceding the fast, a particular diet is followed where carbohydrates that ferment are avoided, thereby allowing for greater accuracy of the test. Breath samples are collected every 15 minutes, for 3 hours, and levels of methane and hydrogen gases are measured.

An elevation in these gases indicates bacteria in the small intestine, which are reacting with the sugar solution used in the test. For people suffering with SIBO, the same is happening when they consume carbohydrates in their diet.  Where the accuracy of the hydrogen gas detected in the test is questionable to some degree, the result of the methane gas in this test is generally accepted to be highly accurate.

Hydrogen gas produced by some bacteria is more often associated with diarrhoea (7), whereas methane gas, produced by other bacteria, is often associated with constipation (8).


Causes of SIBO?

When our digestive system isn’t busy digesting and absorbing nutrients, it’s busy cleaning house.  The migrating motor complex (MMC) is a cyclic motility pattern occurring in the stomach and small intestine - think of the wall of the small intestine causing wave like motions, sweeping contents downwards towards the colon.

If the MMC becomes damaged, this function can be impaired, and bacteria, usually in the colon, can build up in the small intestine. Every time we eat, the MMC is interrupted (9).

Frequent or prolonged use of antibiotics, food intolerances, chronic conditions that affect the wall of the intestinal tract, such as celiac disease or Crohn’s, food poisoning and low stomach acid are all risk factors.


How can we address SIBO?

A diet low in carbohydrates is usually recommended, for example a low FODMAP diet, whereby the very foods that the bacteria react with are removed.

Following this type of strategy can cause a number of other issues in the longer term though, as these carbohydrates also feed our bacteria in the colon, and so we can see changes in our beneficial bacteria levels.

This in turn means we may produce lower levels of beneficial short chain fatty acids, and experience reduced energy levels.

In a nut shell, strategies such as low FODMAP diets aren’t a sustainable, long term solution for dealing with SIBO.

Also of importance is considering that whilst the bacteria are being ‘starved’, they can go into hiding, forming stronger colonies that become more difficult to eradicate.  Short term symptomatic relief can be life changing for SIBO sufferers, but as Nutritional Therapy and Functional Medicine practitioners, we need to tackle the root cause.

An approach that has worked well for our clients is limiting these fermentable carbohydrates in their diet while also working to eradicate the abnormal overgrowth of bacteria in the small intestine.

Studies have shown the efficacy of prescribed antibiotics such as rifaximin, and rifaximin combined with neomycin in treating SIBO.

Unfortunately rifaximin is not an NHS prescribed medication in the UK, but luckily, natural herbal antimicrobial products have been studied and shown to be just as, if not more, effective (10). The type of herbal antimicrobial used, the duration of therapy, and adhering to an appropriate diet for each individual is key to success!

To your lean, healthy, optimised future,





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