IBS is one of the most widespread disorders of the digestive system and impacts the lives of 11% of the global population.  The chronic nature of the condition dramatically impacts the quality of life of those with the condition with over 50% of its suffers having symptoms for over 10 years and 57% of suffers having issues every day.  A diagnosis of IBS can given when an individual meets the symptoms in the Rome IV criteria (see below) but more often it’s diagnosed by excluding other causes of the discomfort such as irritable bowel disease and colon cancer.

IBS Criteria

Recurrent abdominal pain on average at least 1 day/week in the last 3 months, associated with two or more of the following criteria:

1.     Related to defecation

2.     Associated with a change in the frequency of stool

3.     Associated with a change in the form (appearance) of stool




Medications are often used to manage symptoms and are aimed at reducing spasms in the bowel, reducing bowel frequency or improving movements depending on the symptoms.  While some of these avenues can offer benefit less than 25% of patients will experience a reduction in one of their symptoms.

A wide range of factors can influence bowel habits and associated discomfort.  These include; stress, carbohydrate intolerance, vitamin D deficiency, impaired digestive enzyme production and a condition called SIBO.  SIBO stands for small intestinal bacteria overgrowth and is defined by an elevated number of bacteria in the small intestine and is estimated by some to be present in 60-80% of IBS.

We generally find that the number of bacteria increases the further we travel along the digestive tract with a dramatic increase in the large intestine.  However, due to a variety of factors we can find elevated numbers in the small intestine. Our gut in a complex ecosystem with 1000’s of species coexisting in this habitat however we find that once certain bugs start to overgrow or migrate up into the small intestine symptoms can soon follow.  This is a case of the bacteria as a pathobiont – a potentially disease-causing organism which, under normal circumstances lives in harmony with the other bacteria but given the correct circumstances it can over grows and then may cause problems.

When we feed these bugs with fermentable carbohydrates (these are found in many foods but the most troublesome for people are often garlic, onion, leeks, lentils and beans) gas is produced.  This gas production is meant to happen in the large intestine but when it takes place in the small intestine symptoms can results due to the fact that the small intestine is far more sensitive to gas production.

The symptoms of IBS and SIBO are very similar with bloating, constipation, diarrhoea and pain all potentially playing a role and some studies have found SIBO to be present in up 80% of those with IBS.  Due to this high prevalence it’s something I often test for in those with IBS.


Before using anti-microbial herbs to rebalance the gut it’s important to make sure we understand what is going on in your gut.  The test measures 2 types of gas, methane and hydrogen, depending on their levels different approaches may be used.  As is often said, It’s always better to test than it is to guess. The test works by ingesting a liquid which contains a carbohydrate that humans cannot absorb but the bacteria ferment.  If the elevated number of bacteria are indeed present excess gas is produced which is then absorbed into the blood, transferred to the lungs and then can be captured in breath samples which are then analysed by a laboratory.


A low FODMAP diet reduces the amount of fermentable carbohydrates being consumed.  It’s these carbohydrates that the elevated numbers of bacteria in the small intestine feast on and the gas that is produced as a consequence triggers symptoms.  A low FODMAP diet is primarily used to reduce symptoms with the aim to make the individual feeling more comfortable but if SIBO is present it’s not enough to rebalance the gut.  In fact, long term FODMAP restriction has been seen to be detrimental to long term gut health.  A reminded that a restricted diet is a plaster and doesn’t go far enough to address the underlying issue.

Rebalancing the Gut

SIBO can be seen as a condition where the gut bacteria are ‘out of balance’, with too much in the incorrect place.  As relapses of the condition are common it is important to assess and understand what actually brought on the conditions in the first place.  These fall into 4 categories.

  • Impaired motility
  • Impaired digestion
  • Impaired flow
  • Medications

Motility refers to the movement through the small intestine.  We need to think of the gut as a stream rather than a pond.  A stream has fresh flowing water running through it whereas in a pond the water stagnates and favours the build up of bacteria.  Slow movement can be due a number of reasons, most commonly due to a case of food poisoning which has impaired the function of the gut, underactive thyroid or issues as a consequence of diabetes.

Our digestive function can be due to an imbalance of the bacteria (a potential cause and consequence of SIBO), chronic stress which can impair digestive enzyme secretion and immune function.

For the stream to flow smoothly there mustn’t be anything in its way.  Abdominal surgery can leave scaring or adhesions as a consequence as can endometriosis which can prevent smooth movement of stool through the bowel leading to stagnation and bacterial overgrowth.  Also, damage to the valve that separated the small intestine from the large intestine can be damaged which can commonly happen when having an appendix removed.  This value acts as a barrier to separate the two sections however, if it’s not functioning as required the bacteria can slowly creep up into the small bowel.

Various medication can impact our gut and the risk of developing SIBO, these include – opiates/narcotics, antispasmodics, proton pump inhibitors, tricyclic antidepressants.


IBS is a complex issue and while it would be shortsighted to presume everyone has SIBO it is another piece of the puzzle to help unravel this uncomfortable condition.

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