Small Intestinal Bacterial Overgrowth (SIBO) 2018-07-10T15:08:47+00:00

Small Intestinal Bacterial Overgrowth (SIBO)

The entire gastrointestinal tract – a continuous muscular tube through which digesting food is transported on its way to the colon – including the small intestine, normally contains bacteria. The number of bacteria is greatest in the colon (at least 1,000,000,000 bacteria per millilitre (ml) of fluid) and much lower in the small intestine (less than 10,000 bacteria per ml of fluid). You have SIBO if the numbers of bacteria in your small intestine are significantly higher than normal levels.

The muscles of the stomach and small intestine propel food from the stomach, through the small intestine and into the colon. Even when there is no food in the small intestine, this muscular activity continues, which is important for the digestion of food, and also for sweeping bacteria out of the small intestine. The upper gut is supposed to have a low concentration of bacteria, and this Migrating Motor Complex (MMC) is the body’s way of maintaining a low bacterial population in the small intestine. Anything that interferes with the progression of normal muscular activity through the small intestine can lead to Small Intestinal Bacterial Overgrowth.


Causes of SIBO

We now know that in many cases SIBO is a result of acute gastroenteritis or food poisoning but it can also be

  • an effect of surgery (blind loop or ileocecal valve removal)

  • a side-effect of using of Proton-pump Inhibitors (PPIs) such as Omeprazole or Lanzoprazole (prescribed to reduce the secretion of stomach acid)

  • found alongside Coeliac disease or Inflammatory Bowel Diseases.

Simply stated, any condition that interferes with muscular activity in the small intestine allows the bacteria to stay longer and multiply in the small intestine. The lack of muscular activity also may allow bacteria to spread backwards from the colon and into the small intestine.


The main symptoms of this are typically those of:

Latest research suggests that, in many cases, SIBO might underlie Irritable Bowel Syndrome. One study in the American Journal of Gastroenterology found SIBO to be present in 84% of IBS patients tested, although other studies have suggested that this figure may be lower and closer to 50%.

In my clinical experience around 60 – 65% of IBS patients have Small Intestinal Bacterial Overgrowth

Associated disorders

It is also possible that SIBO could be associated with other disorders either as a cause or effect. These may include:

  • Heartburn
  • Nausea
  • Leaky Gut Syndrome
  • Food intolerance
  • Joint pain
  • Fatigue
  • Eczema
  • Asthma
  • Depression
  • Steatorrhea
  • Anaemia (Iron or B12)
  • Acne Rosacea
  • Coeliac Disease
  • Chronic Prostatitis
  • CLL (Chronic Lymphocytic Leukemia)
  • H pylori Infection
  • Heartburn
  • Hypochlorhydria
  • Hypothyroidism / Hashimoto’s Thyroiditis
  • Restless Legs Syndrome
  • Crohn’s Disease
  • Ulcerative Colitis
  • Interstitial Cystitis

As a general rule, if the symptoms of IBS and one of the above conditions are present, then SIBO should be considered.

SIBO Treatment Approaches

There are 4 main treatment approaches for SIBO:


Prescribed by a GP. The typical course is 2 weeks, the antibiotic used in much of the US research is not approved for use in the UK but may be obtained by private prescription and is somewhat costly. SIBO can and often does rebound so antibiotics by themselves can be ineffective in resolving SIBO permanently. It is imperative to combine antibiotics with a low carb style diet to be effective and to achieve a permanent resolution.

Herbal antibiotics

Which may include Enteric coated peppermint, Golden seal, Oregano or Grapefruit Seed Extract. A combination of these is recommended and is very effective. These herbal antibiotics should be taken for a longer period than the antibiotics and can be safely continued for longer periods of time. Many of my patients follow a course of GP prescribed antibiotics with my herbal protocol and this works well.

Specific Carbohydrate Diet (SCD)

This starves the bacteria and takes longer than antibiotics. The length of time needed on the SCD diet varies enormously and can be a number of weeks to several months depending on symptom severity.

Elemental Diet

This involves the use of a liquid diet containing predigested food which is rapidly absorbed in the upper part of the small intestine and in so doing feeds the host and not the bacteria. The diet needs to be taken for 14 days and is considered to be very effective. Unfortunately the shakes are not very pleasant tasting and the cost is very prohibitive for many people.

Each of the SIBO treatment options can be used individually but two or more approaches used simultaneously get the best results.

Small Intestinal Bacterial Overgrowth– frequently asked questions

How does Small Intestinal Bacterial Overgrowth affect us? 2018-02-20T14:34:21+00:00
  1.  The bacteria interfere with normal digestion and nutrient absorption and can damage the intestinal lining causing “Leaky Gut Syndrome”.
  2.  The bacteria consume our food which, over time, leads to deficiencies in nutrients such as iron and B12, causing anaemia and leading to more bacterial overgrowth (a vicious cycle).
  3.  Large volumes of gas are produced in the small intestine or upper gut. This causes abdominal bloating, pain, constipation, diarrhoea or both (the symptoms of IBS), belching and flatulence.
  4. The bacteria also interfere with fat absorption by de-conjugating bile acids, this in turn leads to deficiencies of vitamins A & D and gives the sufferer fatty stools.
  5. As the gut lining is damaged, larger food particles (not able to be fully digested) enter the body, and the immune system reacts to them. This causes food allergies/ sensitivities.
  6. Bacteria themselves can also enter the body/bloodstream. The subsequent immune reaction to bacteria and their cell walls can cause chronic fatigue and body pain and burden the liver.
  7. The bacteria excrete acids which, at high levels, can cause neurological and cognitive symptoms such as brain fog, where you find thoughts hard to process, and which is caused by low-grade inflammation in the brain.
SIBO – is it auto-immune? 2018-05-23T13:31:00+00:00

Small Intestinal Bacterial Overgrowth SIBOAwareness of SIBO has grown enormously in the past 4 years and research in the field has been led by Dr Mark Pimentel of Cedars Sinai Hospital in California and Dr Allison Siebecker of

Dr Mark Pimentel explained the rationale for considering SIBO to be auto-immune in origin at the 2014 SIBO symposium.

It is common for IBS symptoms to be experienced following acute episodes of infectious gastroenteritis or food poisoning. This is considered to be IBS-PI or post infectious IBS. Many patients link their IBS symptoms with being ill on holiday or following a gastro bug or make the link when prompted.

When infected with a gastro bug, the bug creates toxins, and in some instances a person’s immune system makes antibodies to attack and neutralise them. Once the infection has cleared, the antibodies remain in circulation in the body in case they are needed at a later time.

However, the toxin antibodies can mistake a special protein in the wall of the small intestine called – vinculin – needed for normal gut function – for the bug toxins. The immune system then sees the special vinculin proteins as the enemy and attacks them. The antibody attack on the vinculin affects normal gut function and can cause IBS symptoms.

Further research is underway to create a blood test for the vinculin antibody, as this will be a huge help in identifying Post Infectious IBS/SIBO.

Is IBS really SIBO? 2018-02-20T14:30:49+00:00

This question has been posed a lot recently and as a nutritional therapist who specialises in IBS my experience is that SIBO – or some degree of bacterial overgrowth – is present in the majority of IBS patients I see.

For some people, a bacterial overgrowth is the predominant factor in their IBS, whilst other people have what I have termed a Small Intestine Microbial Overgrowth (SIMO).

It’s worth remembering that if you have a motility issue with your small intestine then all forms of microbes, not just bacteria, can overgrow – yeasts and parasites too. In any event, it pays to undergo some clinical tests to identify the type and severity of your own form of SIBO and, once known, this information can guide as to the type of diet and supplements which are most appropriate.

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