Why is my Tummy so Bloated?

If your tummy bloats super-easily and always seems to react to lots of different foods; if it’s sensitive to prebiotics and probiotics; perhaps your gas has got a bit um…. embarrassing!  Well maybe Bacterial Overgrowth of the Small Intestine (SIBO) is the culprit.

Small Intestine Bacterial Overgrowth (SIBO) occurs when too many of certain bacterial strains start to dominate the small intestine and they can interfere with food digestion. This can classically lead to bloating, gas, reflux, nausea, feeling of fullness, loss of appetite, weight loss or gain, gut pain, diarrhoea and constipation. It is one of the primary causes of Irritable Bowel Syndrome.

SIBO is also increasingly known to be part of the picture in cases of chronic fatigue, post viral syndromes, brain fog, anxiety and low mood. Many people with histamine intolerance or low pancreatic elastase (output of pancreatic enzymes) have improved outcomes when any underlying SIBO is addressed.

There are three primary types of SIBO – Hydrogen dominant, Hydrogen Sulfide dominant and Methane dominant. And these very much depend on what strains of bacteria have made their home in your small intestine. It is not always quite so straightforward as the methanogens need hydrogen to grow and thrive, so they often are both present in tandem. Also, there are not currently any tests that can check all three types at once.

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How Do You Test for SIBO?

Breath Tests
This excess of bacteria in the small intestine can lead to the release of gases such as hydrogen and methane (but not hydrogen sulfide yet), which can be identified through a breath test. This is currently offered by some adult gastroenterologists and can also be ordered up via a qualified nutritional therapist, naturopath or functional medicine practitioner.

This test is non-invasive and can be done at home or under the guidance of a gastroenterologist. You need to fast overnight before carrying out this SIBO breath test. And the test involves breathing into a tube, then drinking a specialist sweet drink (lactulose, glucose or fructose), and then breathing into a series of other tubes at regular intervals 2-3 hours after swallowing the drink.

This test is fairly straight forward for adults to do, and you simply need to set aside a morning to complete the test. However, some adults are so unwell or sensitive to the sweet drinks that this stalls them from carrying out a breath test. The breath tests are also harder for young children to do successfully, and a child needs to be quite compliant and mature to do it properly.

New Stool Tests
Thankfully there is now a way round the breath tests, via stool testing which involves collecting one small stool sample which is sent off a laboratory to be analysed. The most progressive of stool tests that we have found so far is the Invivo GI Ecologix which looks at sixty three microbial markers including markers related to Inflammatory Bowel Disease, mucin degradation and gut barrier impairment, Short Chain Fatty Acid production as well as key markers for SIBO, H. pylori, dysbiosis and inflammation. This way of testing is not offered through gastroenterologists or health insurance yet, but is available via nutritional therapists, naturopaths and functional medicine practitioners.

Which Markers Do You Look For In The Stool Test?

The markers which suggest that SIBO is a likely issue may include, Bilophila wadsworthia and Desulfovibrio spp. and to a lesser extent Fusobacterium, which all drive more of the hydrogen sulfide dominant SIBO, and then Methanobrevibacter smithii which is more methane dominant. Hydrogen SIBO is still best to be carried out by a breath test.

Types of SIBOMost Common SymptomPredominant Gas on Breath TestMarkers on Stool Test
Hydrogen Dominant SIBOGeneral, not specific symptomsHydrogen H2
Methane Dominant SIBO Constipation dominantMethane CH4Methanobrevibacter smithii
Hydrogen Sulfide SIBODiarrhoea dominant & rotten egg gasBilophila wadsworthia Desulfovibrio spp.


Hydrogen Sulfide Bacteria – Diet & Support

The hydrogen sulfide bacteria enjoy a high fat and high bile environment and are normally more abundant on diets that are rich in saturated fats, especially dairy, meat and coconut oil. If you eat a more balanced diet, then Bilophila wadsworthia should be really quite low.

The hydrogen sulfate bacteria are more far reaching than the gut and are linked with poor glucose control as well affecting circulation and heart health. However even in the gut these can lead to gut permeability AKA “leaky gut”. A hallmark ‘rotten egg’ smelling gas has been associated with hydrogen sulfide dominant SIBO.

When hydrogen Sulfide bacteria is dominant with high levels of bilophila, desulfovibrio and fusobacterium, then temporary relief can be made by short-term elimination (a few weeks only) of animal based proteins and high-sulphur plant based foods like alliums (onions, chives and garlic), cruciferous vegetables (cabbage, broccoli and cauliflower) and beans/pulses until herbal treatments have reduced the levels of hydrogen Sulfide bacteria. The key four foods for people with excess hydrogen Sulfide bacteria to avoid are garlic, onions, eggs and kale.

Hydrogen Sulfide bacteria also tend to respond well to herbal bitters such as Gentian, Oregon grape and Dandelion root. Antimicrobials may include Uva Ursi, Bismuth, Green Tea, Turmeric and Silvercillin, as well as Zinc and Molybdenum.

Methane Bacteria – Diet & Support

The world is currently worried about how much methane our cows produce, but one of the key high methane gas producers is the human bowel!

In SIBO, Methanobrevibacter smithii will more likely present in a constipation picture as it converts hydrogen into methane which promotes a slow bowel transit. However, it can equally show up in excess amounts when a person is experiencing diarrhoea, bloating, pain and flatulence.

Methanogens grow less in a low pH more acidic gut environment. Methanobrevibacter smithii on the plus side plays an important role in the digestion of polysaccharides (complex sugars) by consuming the end products of bacterial fermentation.

When Methanobrevibacter smithii is first identified and there is more of a sluggish constipation picture, add in flax seeds, chia seeds, hemp seeds, berries, nuts, brown rice, quinoa and green tea as well as kiwi fruit. Herbal blends like Triphala can also help as well as specific blends to help motility.

You can also use natural anti-microbial support such as herbs like Garlic (if Hydrogen Sulfide Bacteria are not present as well), Oregano, Uva Ursi and Neem as well as nano silver.

Prebiotics such as PHGG (Partially Hydrolysed Guar Gum) maybe helpful in methane-dominant SIBO and it has been found to improve the effectiveness of the antibiotic Rifaxamin sometimes used in SIBO treatment and is also excellent for populating the large intestine microbiome.

Table – Herbal/Prebiotic Support for SIBO

Methane Dominant


Hydrogen & Hydrogen Sulfide Dominant


Pomegranate Seeds, Juice & Skin
Artemisia annua
Old Man’s Beard (Usnia Lichen)

I hope this article is helpful to motivate you, and reassures you that you are not doomed to be bloated and gassy forever! If you are keen to organise breath or stool testing or to have help with herbal and nutritional supplements, then do be in touch and book in with one of our NatureDoc practitioners.



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