What is SIBO?
Small Intestinal Bacterial Overgrowth (SIBO) occurs when bacteria that normally live in other parts of the gut begin to overgrow in the small intestine, where they shouldn’t be in large numbers.
There are different types of SIBO, typically classified by the type of gas the bacteria produce – most commonly hydrogen or methane. Hydrogen is more commonly associated with loose stools, while methane is linked with constipation.
What are the symptoms of SIBO?
SIBO can present with a wide range of digestive symptoms, which is why it’s often mistaken for other gut issues.
Common symptoms include:
- Bloating (often worse after eating)
- Excess gas
- Abdominal pain or discomfort
- Diarrhoea, constipation, or alternating between both
But it doesn’t stop there. Many people also experience:
- Fatigue
- Brain fog
- Nausea
- Food sensitivities
- Unexplained weight changes
- Anxiety
Because these symptoms overlap with so many other conditions, it’s important not to self-diagnose.
What causes SIBO?
SIBO isn’t usually the root problem – it’s a sign that something in the digestive system isn’t functioning as it should.
There are many potential underlying causes, including:
- Poor gut motility (how well food and bacteria move through the gut)
- Low stomach acid
- Previous food poisoning or infections
- Chronic stress
- Structural or anatomical issues
If these underlying factors aren’t addressed, SIBO is much more likely to return – even after treatment.
This is why a thorough, personalised assessment is so important. Identifying why SIBO has developed is key to long-term resolution.
How is SIBO tested?
The most common way to test for SIBO is through a breath test. This involves drinking a sugar solution (usually lactulose or glucose) and measuring the levels of hydrogen and methane gases in your breath over a few hours.
Breath testing can be helpful, but it’s not perfect.
There are some important limitations to be aware of:
- False positives can occur, for example if the test reflects normal fermentation in the large intestine rather than the small intestine.
- False negatives can also happen, meaning SIBO may be present even if the test doesn’t detect it.
- Results can be influenced by preparation, timing, and individual gut transit.
Because of this, results should always be interpreted alongside your symptoms and clinical history – not in isolation.
Stool testing is another useful tool. While it doesn’t diagnose SIBO directly, it can identify levels of methane and hydrogen-producing bacteria in the gut, alongside markers of inflammation, digestion, and overall microbiome balance.
In practice, testing is about building a bigger picture. Combining your symptoms, history, and appropriate testing helps create a more accurate and personalised plan.
How is SIBO managed?
Medical treatment often involves antibiotics, which can reduce bacterial overgrowth. However, this isn’t always necessary, and antibiotics alone don’t address the root cause – meaning symptoms can come back.
Herbal antimicrobials are sometimes used as an alternative, but both approaches can disrupt an already sensitive gut microbiome if not used carefully.
Emerging research is now exploring a more supportive approach. Certain probiotic strains and specific types of fibre may help “crowd out” unwanted bacteria in the small intestine, creating a more balanced environment.
The most effective approach is usually a combination of:
- Targeted treatment (when appropriate)
- Supporting the gut environment
- Addressing the root cause
If you’re experiencing ongoing bloating or digestive symptoms and suspect SIBO, getting the right testing and support can make all the difference – not just in managing symptoms, but in preventing them from coming back.
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