Small Intestinal Bacterial Overgrowth (SIBO): Symptoms, Causes & UK Treatment Guide

Small Intestinal Bacterial Overgrowth, commonly known as SIBO, is a digestive condition that occurs when there is an abnormal increase in the overall bacterial population in the small intestine. Under normal circumstances, the small intestine contains relatively few bacteria compared to the large intestine (colon). In patients with SIBO, bacteria—often those typically found in the colon—begin to proliferate in the small intestine.

This bacterial migration interferes with the normal digestive processes. As these bacteria consume nutrients intended for the body, they produce gases such as hydrogen, methane, or hydrogen sulphide. This process leads to the characteristic symptoms of fermentation, including severe bloating, discomfort, and altered bowel habits. While SIBO is increasingly recognised in UK clinical practice, it often mimics other conditions like Irritable Bowel Syndrome (IBS), making a correct diagnosis essential for effective treatment.

The symptoms of SIBO can range from mild discomfort to debilitating nutritional deficiencies. Because the bacteria are active in the small intestine, symptoms often flare up shortly after eating, particularly after consuming carbohydrates or fibres.

Key symptoms reported by UK patients include:

• Abdominal Bloating: A feeling of intense fullness or visible swelling of the stomach, often worsening throughout the day.
• Excessive Flatulence: Passing gas more frequently than usual due to bacterial fermentation.
• Abdominal Pain and Cramping: Discomfort that may be relieved by bowel movements.
• Altered Bowel Habits: This may manifest as chronic diarrhoea, constipation, or a mixture of both.
• Nausea: A persistent feeling of queasiness, particularly after meals.
• Malabsorption Signs: In severe cases, patients may notice oily stools (steatorrhoea), unexplained weight loss, or fatigue due to vitamin B12 or iron deficiencies.

SIBO rarely occurs in isolation; it is typically a secondary symptom of an underlying issue that has disrupted the gut's natural "cleansing" mechanisms. The migrating motor complex (MMC) is a wave of electrical activity that sweeps through the gut between meals, pushing bacteria toward the colon. If this is impaired, SIBO can develop.

Common risk factors identified in NICE and NHS clinical contexts include:

• Structural Issues: Adhesions from previous abdominal surgery, diverticula in the small intestine, or strictures caused by Crohn's disease.
• Motility Disorders: Conditions like gastroparesis or scleroderma that slow down the movement of food and bacteria.
• Systemic Diseases: Uncontrolled diabetes can lead to autonomic neuropathy, affecting gut motility.
• Low Stomach Acid: Chronic use of Proton Pump Inhibitors (PPIs) for acid reflux can reduce the stomach's ability to kill off ingested bacteria.
• Post-Infectious IBS: A bout of food poisoning can sometimes trigger changes in gut motility that lead to SIBO.

Breath Testing

The most common method for diagnosing SIBO in the UK is the Hydrogen and Methane Breath Test. Patients drink a sugar solution (usually lactulose or glucose). If bacteria are present in the small intestine, they ferment the sugar and release gases that are absorbed into the bloodstream and exhaled. Samples are taken at regular intervals; a specific rise in gas levels within the first 90 to 120 minutes indicates SIBO.

Small Bowel Aspiration

While considered the "gold standard," this involves an endoscopy to take a fluid sample directly from the small intestine. Due to its invasive nature and cost, it is rarely used in routine UK practice, with breath testing being the preferred first-line assessment.

Blood Tests

A GP may also order blood tests to check for anaemia or vitamin deficiencies (such as B12, D, and A) which can be a consequence of bacterial overgrowth competing for nutrients.

Treatment for SIBO focuses on three main pillars: eradicating the overgrowth, addressing the underlying cause, and managing symptoms through diet.

• Antibiotics: The most common treatment involves a course of antibiotics. In the UK, Rifaximin is often used because it is non-systemic, meaning it acts primarily within the gut with minimal absorption into the rest of the body.
• Prokinetics: These medications help stimulate the gut's natural cleansing waves to prevent bacteria from returning after antibiotic treatment.
• Dietary Modification: The Low FODMAP Diet is frequently recommended to reduce the "fuel" available to the bacteria. By limiting fermentable carbohydrates, patients can often find significant relief from bloating.
• Addressing the Root Cause: If SIBO is caused by diabetes, surgical adhesions, or medication, these must be managed to prevent recurrence.

If you suffer from chronic bloating that has not responded to standard over-the-counter treatments or basic dietary changes, it may be time to speak to a GP online. Many patients spend years treating "IBS" without realising that SIBO is the true driver of their symptoms.

An online consultation allows you to discuss your symptoms in detail from the comfort of your home. A clinician can review your medical history, discuss the suitability of breath testing, and provide a private prescription for treatments like Rifaximin if appropriate. They can also help you differentiate SIBO from other serious conditions like Coeliac disease or Inflammatory Bowel Disease (IBD), ensuring you follow the correct clinical pathway.