What is SIBO?


sindrome colon Fig1

Small Intestinal Bacterial Overgrowth (SIBO) occurs when there is an abnormal amount of colonic organisms within the small intestine. The term organism includes all living organisms in the small intestine, such as bacteria and fungi. On average, the amount of organisms found in the small intestine is less than 103 organisms/mL(1), whilst the majority of organisms are found in the large intestine. However, with SIBO, the organism that is usually in the large intestine starts to colonise the small intestine where they don’t belong.

The organisms are supposed to reside in the large intestine, where they play an important role in digestion. Since they now reside in the small intestine, they start fermenting on the carbohydrates you consume into hydrogen gases and this may cause an increase in an organism known as archaea (also known as methanogens) which feeds off hydrogen and produces the by-product methane. Both types of gases will result in abdominal pain, bloating, malabsorption and vitamin deficiency symptoms.

The most common form of SIBO is hydrogen, known as hydrogen-dominant SIBO or diarrhoea SIBO. Methane SIBO is not so popular and is known as methane-dominant SIBO or constipation SIBO. Although it’s not wise to assume the SIBO type based on symptoms alone.

There is in fact the third type of gas known as Hydrogen sulfide that may be present in SIBO but is less commonly seen. One recent study showed that the main symptoms associated with hydrogen sulfide are diarrhoea, abdominal pain and a rotten egg smell.

Common Symptoms of SIBO

Symptoms of SIBO closely mirror the symptoms of IBS. A study published in 2000 in the Journal of Gastroenterology reported that 80 per cent of those suffering from IBS were found to have SIBO. The most frequent symptom shown in clinical practice happens to be excessive bloating shortly after eating, usually within 30 minutes.

The most common symptoms are:

  • Bloating within 30 minutes after eating
  • Abdominal bloating/distension
  • Excessive belching
  • Excessive flatulence
  • Abdominal pain/cramping
  • Diarrhoea or constipation or alternating between both
  • Nausea
  • Heartburn

Some non-digestive symptoms that may accompany SIBO are:

  • Rosacea
  • Acne
  • Restless Leg Syndrome
  • Pelvic Pain Syndrome
  • Iron/B12 Deficiency
  • Brain Fog
  • Joint Pain

What Causes SIBO?


The two most important roles stomach acid plays within our body are to break down the food we eat into absorbable components and to protect us from harmful bacteria and spores in our food by killing them off. Hence, a decrease in the production of stomach acid may lead to an increase in the survival of bacteria being able to reach the small intestine.

Another significant cause of SIBO is insufficient bile production. Bile is a fluid that is made and produced in the liver. Its main function is to emulsify fat so that the pancreatic enzyme lipase can further break down fats, also having sufficient bile keeps the small intestine clean since it has anti-microbial properties.

Having a dysfunctional ileocecal valve may contribute towards SIBO as it connects the small intestine to the large intestine. It stays closed for the majority of the time and only opens if there is internal pressure such as a passing bowel movement or gas. If gas is continuously being produced in the small intestine this may place pressure on the ileocecal valve, ensuring the valve stays open for longer, allowing the bacteria in the large intestine to migrate to the small intestine, causing more havoc.

Finally, the most common cause of SIBO is a dysfunctional migrating motor complex (MMC). MMC plays a role in cleaning up the small intestine every 1.5 – 2 hours between meals, moving waste and unwanted bacteria towards the large intestine. If the MMC is unable to play the housekeeping role of the small intestine, this means the bacteria will be able to gorge on the leftover food leading to bacterial overgrowth.


The best way to know if you have SIBO is to get a SIBO breath test, which is a non-invasive test and can be done in the comfort of your own home. If you want to know more about testing, please get in touch with us at the SIBO clinic. Remember healing SIBO is a journey and will not be resolved overnight. If you are ready to start your journey towards managing your SIBO please check out our 16-week programme SIBO Breakthrough Program.

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