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Links between IBS and SIBO (Small Intestinal Bacterial Overgrowth)

by Victoria Tyler(more info)

listed in ibs, originally published in issue 224 - August 2015


Many patients come to my clinic complaining of the inability to eat numerous foods and self-diagnose themselves with food intolerances or food sensitivities. The typical symptoms they describe include bloating, pain, gas diarrhea and constipation.  Many patients also complain that when they eat starches such as bread, and potatoes their symptoms seem to be worse.


Re-Drawn Digestive System

The link between SIBO and IBS

Food intolerances may well be the culprit, however in this article I will talk about another condition linked to IBS called SIBO.

What is SIBO?

SIBO (Small Intestinal Bacterial Overgrowth) is a condition where a large quantity of microbes and bacteria are present in the small intestine.  The small intestine should only contain small amounts of bacteria, large amounts of bacteria are normally found in the colon.  Put simply, if bacteria are found in large amounts in the small bowel, they can cause fermentation resulting in the production of gas and acids.[1]  

Why does SIBO occur?

The exact causes of this condition are still unknown, however we do know that excessive use of antacids can cause bacterial overgrowth.[2] 

Antacids suppress our natural ability to produce acid and this can contribute to the overgrowth of bad bacteria in the small intestine.  Stress can also be a key factor, as when we are stressed we do not secrete as much stomach acid.

In her book, breaking the vicious cycle, Elaine Gottschall[2] explains that bacteria are able to migrate into the small intestine.  This migration may interfere with the digestive process and can also affect absorption of nutrients as well as damage to the gut wall.  This may be another reason why some patients develop leaky gut syndrome, or intestinal permeability.

Dr Mark Pimentel[1] also explains that the small intestine’s cleansing wave mechanism somehow is damaged and can contribute to SIBO. Patients are also at risk of B12 deficiency when microbes overpopulate the small intestine.[2] 

There has also been research pointing to overgrowth of bad bacteria being triggered by acute gastroenteritis or gastritis from infection,  or food poisoning.  These conditions appear to change gut motility thereby leading to an environment where bacterial overgrowth can develop.[3] 

Intestinal Fermentation

In order to truly understand SIBO, it is helpful to look at the fermentation process that occurs in the small intestine. Firstly, bacteria and yeasts will feed off of undigested sugar molecules in the small intestine. For example if you consume a meal with bread, the bacteria will feed off the bread. The next stage will be for the bacteria to cause the release of gases such as hydrogen, methane and carbon dioxide. The bacteria can also cause the production of acids including lactic acid and acetic acid that in turn may injure the small intestine as well as cause behavioural problems and abnormal brain function.[2]

What are the symptoms of SIBO?

These are the most common symptoms associated with SIBO

  • Gas
  • Bloating
  • Burping
  • Belching
  • Constipation
  • Diarrhoea
  • Nausea

Because of the damage to the gut wall from the release of toxins, some patients also develop food intolerances.  There also seems to be a link with mood disorders as well as fatigue and headaches. In extreme cases, patients can also lose weight.[1]  This is linked with inability to properly absorb nutrients  due to the breakdown in the digestive process.

As SIBO becomes more recognized, it is also becoming linked to many other conditions.  In fact, Pimentel believes that IBS (irritable bowel syndrome) is actually a group of symptoms caused by SIBO.  In fact, a study by Pimentel published in the American Journal of Gastroenterology in 2003,[4]  showed that 84% of IBS sufferers had SIBO.  There may also be links to Crohn’s disease, colitis, fibromyalgia and autoimmune conditions.[2] Whether SIBO is a cause or a symptom, it is nevertheless inextricably linked to gut health and overall wellbeing and therefore recognizing it and looking at treatment, is a vital step in the healing process.

How do you know if you have SIBO?

An interesting finding is that some patients report that they feel much better after antibiotic treatment. That is if you have taken antibiotics in the past and felt that your IBS symptoms improved, this could indeed suggest you have SIBO.

A hydrogen breath test is often used to test for SIBO; however, it is not 100% reliable.   Nonetheless, I have found hydrogen breath tests to be extremely useful especially when the patient has negative results on stool tests and other IBS tests.

The hydrogen breath test requires that the patient drink a lactulose or glucose solution after 14 hours of fasting.  The patient’s breath is then measured to assess the presence of methane and hydrogen within 2-3 hours after ingestion.  Higher levels of gas will indicate that the solution was consumed by bacteria in the small intestine.

Treatment for SIBO

If you have tested positive for SIBO, you will certainly need to address your diet.

The aim of treatment involving diet is to try and eradicate and starve the bacteria by reducing their food supply.  In fact, most bacteria require carbohydrates for energy. Once we deprive the bacteria of their food supply they will slowly die and the toxins and products they produce will eventually disappear and the patient will hopefully return to good health.[2]

Of course, a good practitioner should be consulted, as it is important that the patient does not become malnourished during this process.

There are established dietary approaches for doing this, through aiming to reduce the fermentable starches and sugars ingested, which the bacteria love to feed on.

Specifically bacteria tend to eat carbohydrates but they do not eat insoluble fibre.[5]  

Additionally simple sugars such as glucose and fructose may be eaten because they are digested extremely quickly and therefore are not able to be fermented.

This means patients are able to eat honey.

Key Foods to Avoid:

In general the patient is asked to eat a low carbohydrate diet. Foods to avoid include:

  1. Lactose and cheese;
  2. The patient should eat only 3 meals per day. This will help the small intestine rid itself of food residue by the cleansing wave mechanism;[1]
  3. The patient should avoid beans and lentils as these are fermentable;[1]
  4. The patient should avoid Peas;[1]
  5. The patient should avoid soy products.[1]

So what can Patients Eat?

  • The main dietary treatments for SIBO are based on the  Specific Carbohydrate diet[2]
  • the GAPS diet - (this was developed by Dr Campbell-McBride) and  the Low FODMAP diet;
  • Protein such as beef, chicken and fish and small amounts of rice and vegetables are generally allowed. Dr Pimentel also allows two portions of fresh fruit per day;[1]
  • In terms of herbal therapy, there are some very good herbs that are well known for their healing properties and include Oregano oil, Digestive enzymes and Berberine (Goldenseal);
  • Doctors may also prescribe antibiotics such as Rifaximin. However these can be quite expensive, so some patients prefer to take the herbal route.

Lastly it is important to note that may patients with SIBO have difficulty tolerating probiotics. Even though probiotics are touted as being the cure for many digestive disorders, many patients actually feel worse after taking them.


1.Pimentel M. A New IBS Solution. CA. ISBN 0-9774356-0-1 2006

2. Gottschall E. Breaking the vicious cycle, Intestinal Health through Diet. Kirkton Press. Ontario. ISBN 0-9692768-1-8. 1986.

3. Othman M. Agüero R. Lin HC Alterations in Intestinal Microbial Flora and Human Disease. Curr Opin Gastroenterol. 24(1):11-16. 2008.

4. Pimentel M, Chow EJ, Lin HC. Normalization of lactulose breath testing correlates with symptom improvement in irritable bowel syndrome: a double-blind, randomized, placebo-controlled study. Am J Gastroenterol 98:412–419. 2003.



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About Victoria Tyler

Victoria Tyler BSc Hons MBANT received her BSc Hons in Nutritional Therapy from the University of Westminster in London. 

Victoria’s clinic is based in in central London, where she helps patients with gut disorders including IBS and food intolerances.  Victoria has also worked for major high food retailers including Pret a Manger, helping companies provide healthier foods. She also has worked with corporations, Universities and Nursery Schools. Victoria specializes in gut disorders and may be contacted on Tel: 0345 129 7996; her website is:


BSc HONS Nutritional Therapy, London UK

Professional Memberships
BANT- British Association of Nutritional Therapy
CNHC-Complementary and Natural Health Care Council
CNHC-Complementary and Natural Health Care Council

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