Your Simple Guide to Small Intestinal Bacterial Overgrowth (SIBO)

If you have been following TNN for some time now, you would have noticed the significance that your gut health has on your overall health and wellbeing (catch up here). Today we dissect a condition known as Small Intestinal Bacterial Overgrowth (a.k.a SIBO) which is a frequently overlooked contributing factor in several common digestive disorders.

There is no denying that gastrointestinal complaints and discomfort are at an all-time high and unfortunately more often than not, go undiagnosed, incorrectly diagnosed (hello Irritable Bowel Syndrome) or even worse, dismissed by conventional health care clinicians.

Many modern lifestyles factors such as the reliance on antibiotics, stress, abdominal surgery, occurrences of gastroenteritis and overconsumption of refined carbohydrates contribute to a deranged microbiome and a host of health conditions, including SIBO.

So what is SIBO?

As the name implies, SIBO is an overgrowth of bacteria in the small intestine. While bacterium naturally occur throughout the digestive tract, in a healthy system the small intestine should have relatively lower levels of bacteria, with the highest concentrations found in the colon1. This is not the case with SIBO and the excessive amount of bacteria present in the small intestine can cause havoc.

The small intestine is where we absorb nutrients from our food. The increase of bacteria in this region causes nutrients to get broken down and/or fermented (rather than absorbed and used for energy or cell growth and repair) leading to nutritional deficiencies, food sensitivities, gut permeability, poor immune health, inflammation and abdominal discomfort.

SIBO Signs and Symptoms

  • Abdominal pain/discomfort
  • Bloating
  • Flatulence
  • Constipation
  • Diarrhoea
  • Reflux
  • Fatigue
  • Nutrient deficiencies (iron and B12)
  • Altered mood (anxiety and/or depression)

Treating SIBO

SIBO can be diagnosed by undertaking a simple breath test, administered by a health care professional, that measures the levels of hydrogen and methane gas produced in the digestive tract over a period of time. If results are conclusive, dietary change, herbal remedies and lifestyle changes are essential to get the body back into balance and reverse the nutritional deficiencies SIBO may have caused.

The SIBO Bi-Phasic Diet is the most up to date and effective dietary protocol to help eliminate bacterial overgrowth from the small intestine and involves a lower FODMAP (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols), SCD (Specific Carbohydrate Diet) and Dr Allison Siebecker’s SIBO specific food guide2. The Bi-Phasic Diet is broken down into two phases:

Phase 1: this phase involves reducing fermentable starches and fibres, in order to starve bacteria of their preferred fuel source, resulting in die-off. It is based on reducing certain food groups (e.g. dairy, legumes, starchy vegetables, onion, garlic, mushrooms, fruit, grains, sweeteners and specific nuts and seeds), whilst repairing damage to the integrity of the intestinal lining with suitable gut healing nutrients. This phase is divided into two parts (restricted and semi restricted) and individual symptoms will determine how quickly you move through each phase of restriction. Depending on the individual at hand, this phase should take 4-6 weeks in total, before commencing phase 2.

Phase 2: this phase involves the continuation of a low fibre diet (not as restrictive as phase 1) in conjunction with herbal antimicrobials to remove the remaining overgrown bacteria. In this phase, a prokinetic supplement is also recommended to aid the normal functioning of the digestive tract and increase gastrointestinal motility. It is important to note that not all SIBO cases are treated the same and the supplement protocol should differ for individuals who are expressing either hydrogen dominance or methane dominance.

Hydrogen vs Methane Dominance

When you undertake a breath test to diagnose SIBO, the presence of methane and hydrogen gases produced by bacteria in the small intestine is measured after ingesting a sugary solution. For those experiencing hydrogen dominance, the overload and/or the wrong type of bacteria in the small intestines causes the unabsorbed sugar to ferment. The process of fermentation creates hydrogen gas as a by product and this is what the breath test will measure. On the other hand, methane dominance is a little more complex and involves a different class of organisms called archaea. An increase in methane gas after a breath test indicates an overgrowth not of bacteria, but of these methane-producing archaea, which feed off hydrogen and produce methane as a by product3. Another interesting point to note is that symptoms expressed in patients with hydrogen or methane dominance are also linked. More often than not, hydrogen producers are more likely to experience diarrhea and methane producers often struggle with constipation. This is why it is very important that your results are interpreted correctly and we advise you to work with a trained health professional to obtain a safe and effective treatment plan.

What about SIFO?

It is not unlikely for individuals who test positive for SIBO to also experience a co-infection known as SIFO (Small Intestine Fungal Overgrowth). SIFO is similar to SIBO however instead of the presence of excessive bacteria, there is an excessive number of fungal organisms in the small intestine. This condition is also successfully treated with the SIBO Bi-Phasic Diet diet outlined above.

If you think you may be at risk of SIBO or need support in optimising your gut health, please book your complimentary 15-minute consultation with Elyse here. You can learn more about Elyse here.

For more information on this condition, please listen to episode 102 of The Real Food Reel here with SIBO expert Rebecca Coomes.


  1. Hicks, R, 2016. What is small intestinal bacterial overgrowth (SIBO)? WebMD. Accessed 29 May 2017.
  2. Jacobi, N, 2017. The SIBO Bi-Phasic Diet, 1st Ed [PDF] p. 2. Accessed 30 May 2017.
  3. Kresser, C, 2014. RHR: SIBO and Methane—What’s the Connection? Accessed 6 June 2017.

Image credit here.

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