SIBO : Types of Bacterial Overgrowth

Small intestinal bacterial overgrowth, or SIBO, is a digestive imbalance I commonly see and treat in my practice. As a clinical herbalist I use herbal medicine, select prebiotics and targeted probiotic strains to help overcome this persistent microbiome imbalance.

Today we are following on in our SIBO series of videos and I will be covering the different types of small intestinal bacterial overgrowth. To check out the whole video series head over here and don’t forget there is an ebook that goes along with the videos which you can download free in all its 10,000+ words and 60+ references!

The Complete Guide To Small Intestinal Bacterial Overgrowth


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Hi, my name is Todd Mansfield. I am a clinical herbalist with a special interest in all things gut health.

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Types Of SIBO

SIBO is more of a collection of different subtypes of microbial overgrowth. I have come to see small intestinal bacterial overgrowth as a symptom of a deeper dysregulation in most of my patients. Today we won’t be covering the possible root causes of your SIBO but it is worth mentioning. When the root cause is not addressed often SIBO relapses!

Hydrogen SIBO

Hydrogen SIBO, hydrogen dominant SIBO or even diarrhoea SIBO is the more common form of bacterial overgrowth in the small intestine. It is characterised by an abnormal rise in hydrogen on the SIBO breath test after a challenge with a particular sugar (often lactulose or glucose). Don’t worry we will be covering SIBO testing in an upcoming video.

The symptoms include bloating and distention, an increase in flatulence and burping and even non-gut related symptoms like brain fog, unclear thinking or even joint pain. If any of these symptoms worsen after a meal I am thinking SIBO may be playing a role.

The number one symptom that distinguishes hydrogen SIBO from the other most common SIBO is diarrhoea. Loose stools, combined with the symptoms above, is frequently caused by the hydrogen producing bacterial overgrowth in the small intestine.

Methane SIBO

Methane SIBO, also known as methane dominant SIBO or even constipation SIBO is characterised by a significant amount of methane gas on a SIBO breath test. The number one symptom that sets methane SIBO apart from other types of bacterial overgrowths is constipation.

On a side note, but still very methane related, I commonly see a high baseline methane levels (greater than 20ppm) on many SIBO breath tests from patients suffering from long term constipation. The thinking here differs. Some clinicians and researchers think that it is large bowel methane production while others are thinking it is small bowel related.

The North American Consensus on breath testing was a tad unclear.

The optimal criterion to define excessive methane production is not clear. Th e production pattern of methane and hydrogen are different on breath testing. Unlike hydrogen, subjects with excessive methane production elicit an elevated methane level at baseline and the rise of methane during breath testing is not as sharp as hydrogen gas

The North American Consensus

They go on to note that until we have more research on the subject any level of methane of or above 10 ppm on a breath test should be considered positive for methane. They do not note whether this is large bowel or small bowel. Not so relevant as a herbalist as the select herbs treat methane both in the small and large bowel simultaneously. Below is a great example of a high baseline methane SIBO breath test. Is this small bowel or large bowel? We still aren’t quite sure.

High baseline methane on a SIBO breath test.

Hydrogen Sulphide SIBO

Hydrogen sulphide SIBO, also known as hydrogen sulfide SIBO or H2S SIBO is still quite the enigma and I will tell you why. We still don’t have the breath testing available to test for it. Don’t worry it is being developed as we speak.

With the limited evidence available hydrogen sulphide SIBO appears to be linked to diarrhoea and urgency as this particular gas is a smooth muscle relaxant (2). The current thinking is a cut of of 1.2ppm of hydrogen sulphide (H2S) using SIBO breath testing (3) but these are early days.

It is a bit of a concern that we still don’t have the breath testing available to test for this particular gas. My current workaround, and I will be the first to admit it isn’t perfect, is to analyse the large bowel for hydrogen sulphide producers in patients that I suspect have hydrogen sulphide SIBO. While it isn’t a guarantee that the small bowel will match the large bowel’s hydrogen sulphide producers it can help to explain flatlined breath testing results.

Below is an image of a microba large bowel analysis (available in Australia only at the moment) showing moderately elevated levels of the two more common hydrogen sulphide producers, Bilophila wadsworthia and Desulfovibrio sp. Check out more on hydrogen sulphide production and learn more about Bilophila wadsworthia here.

Hydrogen sulphide overgrowth in the large bowel.

Small Intestinal Fungal Overgrowth

Small intestinal fungal overgrowth or SIFO is the fourth for of microbial overgrowth that can occur in the small bowel. As such it somewhat falls under the SIBO banner.

The most common symptoms of fungal overgrowth in the small intestine are abdominal pain, gas, bloating, flatulence, and diarrhoea (4). One study found that approximately 25% of patients with chronic gut symptoms had SIFO (mainly Candida species) (5).

In the literature the leading causes of SIFO appear to be dysmotility and proton pump inhibitors (6) as well as colectomy surgery (7). As with hydrogen sulphide SIBO this is early on in our understanding of small intestinal fungal overgrowth. I will be putting together more on the subject shortly so stay tuned and remember if you are looking for support with your chronic digestive symptoms bookings can be made here.

References and Resources

  1. Hydrogen and Methane-Based Breath Testing in Gastrointestinal Disorders: The North American Consensus
  2. USING A NOVEL 4-GAS BREATH TEST DEVICE, MULTIVARIABLE ANALYSIS REVEALS AN ASSOCIATION BETWEEN EXCESSIVE HYDROGEN SULFIDE ON BREATH TESTING AND HEARTBURN
  3. THE FIRST STUDY TO DETERMINE THE NORMAL RANGE OF EXHALED HYDROGEN SULFIDE (H2S) USING A NOVEL 4-GAS BREATH TEST DEVICE IN HEALTHY SUBJECTS
  4. Small Intestinal Fungal Overgrowth
  5. Small Intestinal Fungal Overgrowth (SIFO): A Cause of Gastrointestinal Symptoms
  6. Dysmotility and ppi use are independent risk factors for small intestinal bacterial and/or fungal overgrowth
  7. Small Intestinal Bacterial Overgrowth (SIBO) and Fungal Overgrowth (SIFO): A Frequent and Unrecognized Complication of Colectomy

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