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Small intestinal bacterial overgrowth (SIBO)

Small Intestinal Bacterial Overgrowth (SIBO) is an often overlooked test by GPs and healthcare practitioners who often focus far too much attention on the large bowel.



We often see clients with SIBO who have been undiagnosed and/or labelled with IBS (which is just a syndrome) for many years before coming to see us.

The small intestine bacterial overgrowth test measures breath levels of hydrogen and methane to determine if a bacterial infection is present in the small intestine. The test differs from a stool test in that it tests for imbalance in the small intestine rather than the large. Small intestinal bacterial overgrowth occurs when bacteria from the large intestine travel to the small intestine, often the result of poor hydrochloric acid production in the stomach or an insufficient amount of pancreatic enzyme function. It is often found in conjunction with parasitic infections. Chronic pancreatitis, Crohn’s disease and lupus erythematosus can also cause small bowel overgrowth.

Symptoms of SIBO

  • Bloating and distention
  • Wind
  • Diarrhoea or constipation
  • Abdominal pain and cramping
  • Food intolerance
  • Nutrient deficiencies
  • Fat malabsorption
  • Fatigue
  • Weight loss

What causes SIBO?

  • Decreased motility in the small intestine – a muscular action called migrating motor complex propels food through the digestive tract, sweeping large numbers of bacteria through the small intestine and into the colon. When a lack of motility is present, bacteria may either remain in the small intestine for too long, where it multiplies, or bacteria from the colon can re-enter the small intestine. While health conditions like hypothyroidism and diabetes can slow motility, the main cause of decreased motility is the pathogenic bacteria present during acute gastroenteritis. Such bacteria secrete a toxin called Cytolethal Distending Toxin, or CDT, and a portion of this toxin actually resembles a protein that sits on the nerve cells that regulate the migrating motor complex. Through a process called molecular mimicry, the immune system gets confused and attacks the protein at the same time as attacking CDT, damaging the nerve cells. Damage from repeated attacks of acute gastroenteritis can be cumulative during ones lifetime, which is why SIBO tends to affect adults rather than children. About 50% of people affected in this way will spontaneously recover because the nerve cells have a high degree of plasticity, meaning they can change and heal, although it can take several years.
  • Obstruction – this refers to anything that could block the pathway for bacteria to travel down into the large intestine, including a tumour, scar band, inflammation caused by Crohn’s disease, adhesion or hairpin turn in the small intestine.
  • Non-draining pockets – this includes surgical blind loops and diverticulitis, a condition that creates pouch pockets off the side of the GI tract that can collect water and debris.
  • Low Stomach Acid.
  • Long history of constipation.
  • An initial bout of food poisoning or gastroenteritis.

People with SIBO experience diarrhoea, bloating, poor nutrient absorption and weight loss. Other people that may be affected are those with poor ileocecal valve function, poor intestinal motility, scleroderma, or recent gastric surgery. People with SIBO often have difficulty with digestion of fats, which come through undigested in the stool, called steatorrhea. They may also experience B12 deficiency, chronic diarrhoea and poor absorption of the fat soluble vitamins A, D, E, and K.

Breath testing provides a simple, non-invasive alternative to the more widely used method of obtaining a small bowel aspirate and is more accurate. To perform the test, you drink either a lactulose or a glucose drink and collect breath samples. Hydrogen is produced when lactulose or glucose come in contact with the gut flora. A significant rise in the Hydrogen levels indicates SIBO.

What dietary measures are good for SIBO?

Low FODMAPS alongside SCD diet are a useful dietary measure for SIBO amongst other approaches but must be combined with bowel motility and anti-microbial programme.

Self help for SIBO prevention

  • Avoid antacid medication as much as possible.
  • Effectively treat any health conditions that slow motility, such as hypothyroidism and diabetes.
  • Avoid excess sugars and starchy carbohydrates, and limit alcohol consumption.
  • Avoid unnecessary snacking between meals, especially on sugary/starchy foods.
  • Manage stress levels to prevent stress-induced changes to digestive function.
  • Take a natural anti-microbial, such as allicin or berberine, when travelling or during acute gastroenteritis.
  • Leave 5 hours between each meal.

What is the treatment for SIBO?

SIBO is treated using anti-microbials followed by bile and pancreatic support. This is then followed by a gut healing program and stress reduction techniques. Also it is necessary especially in methane based SIBO to improve the function of the Migrating Motor complex (MMC) For further info on testing see here.

Latest research shows herbal medicine as or more effective than antibiotics: Chedid V, Dhalla S, Clarke JO, et al. Herbal therapy is equivalent to rifaximin for the treatment of small intestinal bacterial overgrowth.

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