IBS and SIBO (Small Intestinal Bacteria Overgrowth) – is there a connection?

Embarrassing gas, painful bloating, constipation, diarrhoea (or both) – if you have been diagnosed with Irritable Bowel Syndrome (IBS)  you are most likely very familiar with all these symptoms and you are not alone. Up to 20% of the worlds population suffer with IBS.

But what causes IBS?

If you have a diagnosis of IBS you know how frustrating it is for doctors to shrug their shoulders as to the cause and just prescribe medications to help with the symptoms, that often don’t work very well.

However, over the last few years more research has gone into the causes of IBS and scientists have discovered that in up to 60-80%1,2 of IBS cases Small Intestinal Bacteria Overgrowth (SIBO for short) is the cause of the IBS. While SIBO hasn’t quite hit mainstream GP practices it is gaining traction and more are getting tested for it.

So is your IBS really SIBO? What is the connection? 

Firstly, what is SIBO?

SIBO, or small intestinal bacterial overgrowth, occurs when there is an overgrowth of bacteria in the small intestine. Intestinal Methanogen Overgrowth (IMO) is similar to SIBO, but with an overgrowth of methane producing bacteria (archaea) causing a slower transit time and constipation.

Whilst you may have heard, or read into, different ways you can support your intestinal health within the large intestine by eating different foods etc you may not have read much about the effect bacteria levels in our small intestine may have on your gut health.

The truth is the majority of our gut bacteria is found in the large intestine, not the small intestine. The small intestine is where our body gets the chance to breakdown and absorb the nutrients we need from our food. Bacteria, if present, would just compete for those nutrients.

With SIBO / IMO bacteria or archaea start to flourish in the small intestine due to the reduced activity of the ‘housekeeping’ wave, AKA the Migrating Motor Complex (MMC). The MMC should keep moving the contents of the small intestines along until it reaches the large intestine. When it’s not working like it should the foods is left there for longer and the small amounts of bacteria in the small intestine flourish with this food source.


 How does SIBO/IMO make me feel bad? What are the symptoms?

When the bacteria in your small intestine feed off the nutrients in the food, they produce gas as they consume it. This is called fermentation. With no easy route out for the gas, this results in on-going bloating, acid reflux and ultimately, changes in bowel movements.

This gas is what causes symptoms of:

  • Bloating and Distension
  • Gas – burping mostly, but also wind
  • Diarrhoea and / or constipation

Other symptoms or complications of SIBO/IMO can include:

  • Weight loss (due to nutrient deficiency)
  • Weight gain (due to a slowing down of the metabolism)
  • Feeling overfull, even after small amounts of food
  • Pain and hypersensitivity
  • Acid reflux (when the gas can’t get out, it looks for an easy exit, which often times is out through the stomach)
  • Nausea
  • Fatigue
  • Depression / Anxiety
  • Food Intolerances
  • Skin reactions (eczema, psoriasis, rosacea)
  • Restless leg syndrome

 So what causes SIBO to develop?

As I’ve mentioned already, the majority of our gut bacteria live in the large intestine. SIBO can flourish due to factors that can cause the bacteria to migrate to areas that it shouldn’t, or due to factors that change the gut diversity altogether.

 One of the main causes of SIBO is what’s known as Post-Infectious IBS, or food poisoning.

 The bacteria that causes food poisoning contain a toxin called cytolethal distending toxin (CDT). Part of this toxin looks very similar to a protein called vinculin. This protein is contained in the cells of the small intestine.

When the immune system mounts it s attack on the CDT following a food poisoning event, the immune system also attacks the vinculin, as they look the same. This destruction of the vinculin causes the migrating motor complex (MMC) to be compromised, as the vinculin is the protein that turns this on.

While food poisoning is one of the most common causes for SIBO, anything that disrupts the normal flow of food and bacteria through the digestive system can also cause SIBO. These include:

  • Lack of digestive enzymes and stomach acid – this leads to poor digestion of food, leaving it to ferment. Medicines that lower stomach acid, such as PPI’s will also do this.
  • Endometriosis (which can cause scars called adhesions which alter the flow of bacteria)
  • Poor gut motility – you don’t necessarily need to be constipated for this to be poor
  • Hypothyroidism – resulting in an overall slowing of digestion and motility
  • Autoimmune conditions such as Coeliac disease
  • Traumatic Brain Injury (this can affect the MMC)
  • Physical abnormalities from abdominal surgery (again due to adhesions)
  • Overuse of Antibiotics (which are known to change the diversity of the gut bacteria)
  • Other imbalances in the gut such as Yeasts and Parasites

 Could it be SIBO? How to find out for sure.

 If you have any of the symptoms outlined above I would strongly recommend testing for SIBO / IMO, even to rule it out.

The test itself is a simple breath test, where by you drink a solution of lactulose and then take a breath sample every 15 minutes over 2-3 hours (for this reason it is recommended to have the test performed in a lab, but if that is not possible it can be done at home). GastroLife is the main lab here in Ireland and you can order directly from them.

 If you do have SIBO, what can be done about it?

 There are many ways you can help support your body to deal with SIBO, to reduce symptoms and to prevent a re-occurrence. However, with a positive SIBO result treating it with an antibiotic or an appropriate  anti-microbial herbal supplement, along with dietary changes and supports, is the only way to eradicate it long-term. In studies, the natural herbal supplements have been shown to be as effective as the antibiotic3. Bear in mind, with whatever course of treatment you chose several courses of either may be required.

Both these routes need to be supported with improving gut function and replenishing the good gut bacteria to avoid a relapse, such as:

  • Supporting and restoring digestion, both by adding in supplements as well as changing eating intervals
  • Restoring regular bowel movements with diet and lifestyle changes,
  • Adding in prokinetic agents to re-establish proper MMC function such as Ginger
  • Lowering fermentable carbohydrates in the diet to remove some of the food for the bacteria (this will mainly lower symptoms of bloating)
  • Supporting the immune system so that it can fight future infections
  • Calming down inflammation caused by the overgrowth and promoting healing

 Knowing that SIBO is the cause of up to 80% of all IBS cases, isn’t it time that you found out if it is causing yours?

If you have already ruled out other causes for your IBS and you have tried other dietary measures to no avail, SIBO may be part of the reason and it is worth being tested for it.

 If you would like to know more about SIBO and to find out if that is what is causing your IBS then book a discovery call with me today. It’s time to get the help you deserve and start living the life you want to live!

  1. Peralta S et al. Small intestine bacterial overgrowth and irritable bowel syndrome-related symptoms: experience with Rifaximin. World J Gastroenterol. 2009 Jun 7;15(21):2628–2631.
  2. Lin HC et al. Small intestinal bacterial overgrowth: a framework for understanding irritable bowel syndrome. JAMA. 2004 Aug 18;292(7):852– 858.
  3. Mullin GE, Chedid V et al. Herbal therapy is equivalent to rifaximin for the treatment of small intestinal bacterial overgrowth. Global Advances in Health & Medicine. 2014 May; 3(3): 16-24. Published online 2014 May 1. Doi: 10.7453/gahmj.2014.019

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