Small intestinal bacterial overgrowth (SIBO): when the bacteria are in the wrong place

SIBO (Small Intestinal Bacterial Overgrowth) is a condition in which an excessive amount of bacteria develops in the small intestine that should normally be found mainly in the large intestine. This leads to impaired digestion, fermentation of food and a variety of often underestimated symptoms. A growing body of research suggests that SIBO is behind a large proportion of cases of chronic gastrointestinal complaints that have long been labelled as „functional“.

What are the main symptoms?

SIBO can manifest in different ways, but most commonly patients report:

• bloating (often soon after eating)
• gas and abdominal discomfort
• diarrhea, constipation or alternation of both
• feeling of „heaviness“ and incomplete digestion
• fatigue, brain fog
• vitamin deficiencies (B12, iron, fat-soluble vitamins)
• skin problems, anxiety, low mood

It's important to know that SIBO doesn't just affect the gut, it can affect overall health.

Why SIBO appears?

SIBO is not a disease in its own right, but the result of impaired defence mechanisms of the small intestine.

The most common reasons include:

• delayed intestinal motility
• irritable bowel syndrome (IBS)
• chronic stress
• hormonal disorders
• frequent use of antibiotics
• low stomach acid
• abdominal operations
• diabetes and other metabolic diseases

A key mechanism is the disruption of the so-called migrating motor complex (MMC) - the „cleaning mechanism“ of the small intestine between meals.

Types of SIBO

Depending on the dominant gases are distinguished:

• Hydrogen-dominant SIBO - more often with diarrhea
• Methane-dominant SIBO (IMO) - more often with constipation
• Hydrogen sulphide SIBO - more difficult to diagnose, often with severe pain and diarrhea

This is important because treatment differs according to type.

How is it diagnosed?

The gold standard in clinical practice is the glucose or lactulose breath test, which measures hydrogen and methane in exhaled air.

It is important that the test be:

• properly prepared
• correctly interpreted
• correlated with symptoms

A test alone without clinical evaluation often leads to erroneous conclusions.

Why does the standard advice „eat more fiber“ often make SIBO worse?

In SIBO, fiber and fermentable carbohydrates can feed the bacteria in the small intestine instead of helping.

So:

• some „healthy“ foods temporarily worsen symptoms
• diets like Low FODMAP may bring relief but do not cure the cause
• long-term fibre restriction is not a solution

What is involved in the treatment of SIBO?

An effective approach is individual and phased, and may include:

• antibacterial therapy (pharmaceutical or herbal)
• correction of intestinal motility
• diet according to the condition
• restoration of the intestinal barrier
• careful use of probiotics (not for everyone)
• stress management

It is important to emphasize that SIBO often relapses if the root cause is not addressed.

Why is SIBO important to be recognized in time?

Untreated SIBO can lead to:

• chronic inflammation
• malnutrition
• hormonal disorders
• impaired quality of life

Early recognition and the right approach significantly improve prognosis.

Conclusion

SIBO is a real, often underestimated condition that requires medical thinking, not one-size-fits-all advice. If you have chronic digestive symptoms that are not responding to standard recommendations, it is important to look for a deeper cause.

Sources

1. Pimentel M. et al. Small Intestinal Bacterial Overgrowth: A Comprehensive Review. Gastroenterology, 2020
2. Rezaie A. et al. Hydrogen and Methane-Based Breath Testing in GI Disorders. Am J Gastroenterol, 2017
3. Ghoshal UC et al. Small intestinal bacterial overgrowth and IBS. Gut and Liver, 2017
4. Quigley EMM. The gut microbiota and the brain-gut axis. Gastroenterology, 2019
5. Rao SSC et al. Diagnosis and management of SIBO. Gastroenterology Clinics, 2021