Disclaimer: This is general health information only and is not a substitute for advice from your GP or healthcare professional.
1. What is SIBO?
SIBO stands for small intestinal bacterial overgrowth. While the large intestine normally contains large numbers of bacteria, the small intestine should have relatively few. SIBO occurs when bacteria migrate from the colon into the small intestine or when normal small-intestinal bacteria multiply excessively. These bacteria ferment food too early in digestion, leading to gas production, bloating, and impaired nutrient absorption.
2. What causes SIBO?
SIBO is usually a secondary condition caused by problems with normal gut “housekeeping.” The most common cause is impaired gut motility, particularly dysfunction of the migrating motor complex (MMC), which is the cleansing wave that clears bacteria from the small intestine between meals. Other causes include structural changes such as adhesions, strictures, or diverticula, systemic diseases like diabetes or scleroderma, and long-term use of medications such as proton pump inhibitors, which reduce stomach acid that normally helps limit bacterial growth.
3. What are the common symptoms of SIBO?
Symptoms often overlap with irritable bowel syndrome. Common symptoms include significant bloating that worsens as the day progresses, excessive gas, abdominal discomfort, and changes in bowel habits. Hydrogen-predominant overgrowth is more commonly associated with diarrhoea, while methane-predominant overgrowth, now often referred to as intestinal methanogen overgrowth (IMO), is more commonly associated with constipation.
4. How is SIBO diagnosed?
SIBO is most commonly diagnosed using hydrogen and methane breath testing. After fasting and following a specific preparation diet, a sugar solution such as lactulose or glucose is consumed. If bacteria or methanogens are present in the small intestine, they ferment the sugar and produce gases that are absorbed into the bloodstream and exhaled, allowing measurement over time.
5. Is SIBO serious?
SIBO is not usually life-threatening, but chronic untreated SIBO can lead to significant health problems. Bacterial overgrowth can interfere with absorption of nutrients such as vitamin B12 and iron, leading to anaemia, and can impair fat absorption, resulting in deficiencies of fat-soluble vitamins including vitamins A, D, and E.
6. How is SIBO treated?
Treatment focuses on reducing the overgrowth and preventing recurrence. This usually includes targeted antibiotics such as rifaximin, dietary strategies such as a temporary low-FODMAP or elemental diet, and treatment of underlying causes. Medications that improve gut motility, known as prokinetics, are often used to support the migrating motor complex and reduce relapse risk.
7. Can SIBO be cured?
SIBO can often be cleared with appropriate treatment, but it commonly recurs if the underlying cause is not addressed. Long-term management focuses on restoring normal gut motility, addressing structural or systemic conditions, and supporting the body’s natural ability to keep the small intestine clear of excess bacteria.
8. When should I see a doctor?
You should see a doctor if you experience persistent or severe bloating, unexplained weight loss, ongoing diarrhoea or constipation, or symptoms that do not respond to standard dietary changes or supplements. Medical assessment is particularly important if you have had abdominal surgery or have conditions such as Crohn’s disease or diabetes.
9. Why does SIBO frequently recur?
SIBO often recurs because the migrating motor complex is not functioning effectively. If the small intestine is not regularly cleared between meals, bacteria and methanogens can migrate back from the colon. Strategies such as meal spacing, prokinetic medications, and treating underlying motility disorders are commonly used to reduce recurrence.
10. What are the possible complications of SIBO?
Complications of chronic SIBO include vitamin and mineral deficiencies, reduced bone density due to vitamin D and calcium malabsorption, neurological symptoms from severe vitamin B12 deficiency, unintended weight loss, and increasing food intolerances due to damage to the intestinal lining. Early diagnosis and appropriate treatment help minimise these risks.