SIBO stands for small intestinal bacterial overgrowth. It describes a situation where excessive bacteria, or the wrong pattern of bacteria, are present in the small intestine. Because the small intestine is where many nutrients are absorbed, bacterial fermentation there can cause bloating, gas, abdominal pain, diarrhoea, constipation, or nutritional problems.

SIBO is real, but it is also over-applied online. Bloating after meals does not automatically mean SIBO. IBS, constipation, functional dyspepsia, reflux, coeliac disease, inflammatory bowel disease, medication effects, and ordinary food intolerance patterns can look similar.

Key takeaways:

  • SIBO can cause bloating, gas, pain, diarrhoea, constipation, and sometimes nutrient issues.
  • Breath testing is commonly used, but results need careful interpretation.
  • Diet may reduce symptoms, but it does not address every underlying cause.
  • Suspected SIBO is best handled with a clinician rather than repeated self-treatment.

What causes SIBO?

Your small intestine normally has fewer bacteria than your colon. Several protective systems help maintain that balance: stomach acid, bile, pancreatic enzymes, gut motility, the migrating motor complex, the ileocaecal valve, and immune function.

SIBO risk can increase when these systems are disrupted. Examples include previous gut surgery, strictures, motility disorders, diabetes-related nerve changes, certain medications, low stomach acid, immune problems, or adhesions. Some people develop SIBO-like symptoms after gastroenteritis.

In many cases, SIBO is not just a bacterial problem. It is a motility or anatomy problem that allows bacterial overgrowth to recur.

Common SIBO symptoms

The symptom most associated with SIBO is bloating that worsens after eating. Gas, abdominal pain, diarrhoea, constipation, reflux, nausea, and food intolerance can also occur. Some people report fatigue or brain fog, although those symptoms are non-specific.

More concerning signs include weight loss, nutrient deficiencies, anaemia, greasy stools, persistent diarrhoea, or symptoms after previous bowel surgery. These deserve medical assessment.

Testing and diagnosis

Breath tests measure hydrogen and methane gases after you drink a sugar solution such as lactulose or glucose. The idea is that bacteria ferment the sugar and produce gases that are absorbed into the bloodstream and breathed out.

Breath tests can be useful, but they are imperfect. Preparation matters, transit time can confuse results, and different labs use different cut-offs. A positive test should be interpreted alongside symptoms and medical history.

Some clinicians may investigate other causes first, especially coeliac disease, inflammatory bowel disease, pancreatic insufficiency, or thyroid disease, depending on your symptoms.

Diet, antibiotics, and recurrence

Antibiotics such as rifaximin are sometimes used for SIBO, particularly hydrogen-dominant patterns. Methane-dominant constipation patterns may be treated differently. These decisions should be made with a healthcare professional.

Diet can reduce fermentation and symptoms, but very restrictive diets are not a long-term solution for everyone. Low-FODMAP, specific carbohydrate, or other approaches may help some people short term, but they can also reduce variety and increase food fear.

Recurrence is common if the underlying driver is not addressed. Motility, constipation, medication review, and structural issues may matter as much as the bacterial load.

What to do next

If you suspect SIBO, discuss testing and treatment with a GP, gastroenterologist, or qualified dietitian. If you are mainly dealing with bloating but no red flags, start with a broader view of bloating causes before assuming overgrowth.

GutFix can help after medical assessment by identifying which foods and portions worsen symptoms for you, without treating every food reaction as proof of SIBO.

This article is for educational purposes only and does not constitute medical advice. Consult a qualified healthcare professional for personalised guidance.