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Gluten-free diet and small intestinal bacterial overgrowth (SIBO): diagnosis and treatment

We explain what SIBO is and the relevance of a gluten-free diet in the management of this condition.

Gluten-free diet and small intestinal bacterial overgrowth (SIBO): Is there a link?

A gluten-free diet can provide relief for various gastrointestinal conditions. However, in patients with small intestinal bacterial overgrowth (SIBO) or irritable bowel syndrome (IBS), determining whether this dietary intervention is appropriate can be particularly complex. In clinical practice, the challenge is not only to identify whether SIBO is present, but also to understand what role diet-including a gluten-free diet-can play within a broader approach.

Detection of small intestinal bacterial overgrowth (SIBO): the first step in the approach

Small intestinal bacterial overgrowth is characterised by excessive proliferation of bacteria in the small intestine. This condition usually presents with symptoms such as bloating and abdominal distension, resulting from gas production by these bacteria.

Other common symptoms include:

  • Abdominal pain or discomfort
  • Diarrhoea or constipation
  • Flatulence
  • Belching
  • Feeling of incomplete bowel movement
  • Dyspepsia

It is important to note that symptoms can vary between patients and overlap significantly with gluten-related disorders, which complicates the differential diagnosis.

Various conditions can increase the risk of developing SIBO, including diabetes, chronic inflammatory diseases and gastrointestinal conditions such as inflammatory bowel disease, chronic constipation or coeliac disease. It has also been linked to non-coeliac gluten sensitivity, wheat allergy, IBS and prolonged use of antibiotics or antacids.

Furthermore, some studies have observed a high incidence of SIBO in patients with coeliac disease who continue to experience symptoms despite following a gluten-free diet.

SIBO testing: how bacterial overgrowth is diagnosed

SIBO can be diagnosed using various techniques:

  • The gold standard method is small bowel aspirate culture, although its use is limited as it is an invasive, costly procedure with a risk of contamination.
  • In clinical practice, the most common approach is to use the breath test (hydrogen breath test). This test involves administering a substrate, usually glucose or lactulose, after which breath samples are analysed in a series of tests.

A significant increase in hydrogen or methane compared to baseline values is considered consistent with SIBO. In some cases, hydrogen sulphide may also be assessed, particularly in patients with predominantly diarrhoea, although this measurement is less common.

The relationship between IBS and SIBO: why it is crucial to take it into account

Irritable bowel syndrome is a common and heterogeneous disorder, characterised by symptoms such as abdominal pain, bloating, diarrhoea and/or constipation. Its diagnosis is clinical, as there are no specific biomarkers, and is based on the patient’s history and symptoms. Factors such as stress, anxiety, previous gastrointestinal infections or intestinal inflammation may influence its development.

In this context, it has been suggested that SIBO and IBS may form part of the same pathophysiological spectrum. Some research suggests that a significant proportion of patients with IBS also have SIBO, which could explain some of their symptoms.

It is estimated that up to 50% of patients with IBS may have SIBO, which opens the door to the possibility that treating bacterial overgrowth could help improve symptoms in this subgroup.

Treatment of bacterial overgrowth

The approach to SIBO should focus, first and foremost, on identifying and treating the underlying cause.

For example, in patients with coeliac disease or other gluten-related disorders, a gluten-free diet is a fundamental part of treatment. Once the cause has been addressed, antibiotics may be used to reduce the bacterial load.

In some patients, other complementary strategies have also been explored, such as the use of probiotics, prokinetic agents, digestive enzymes, or interventions aimed at managing stress and intestinal motility.

Hands holding a colorful illustration of intestines filled with capsules and microorganisms against a light background

A patient-centred approach:

the importance of tailoring each strategy

Dietary approaches to SIBO and IBS must be tailored to the individual. Not all patients respond in the same way to a gluten-free diet or a low-FODMAP diet.

Furthermore, as a gluten-free diet can be restrictive, its long-term use should be reserved for those patients who experience clear clinical improvement. In these cases, it is important to ensure proper dietary planning, avoiding highly processed or FODMAP-rich products.

Beyond specific interventions, the long-term approach usually includes general recommendations such as prioritising minimally processed foods, maintaining a balanced diet, engaging in regular physical activity, managing stress, and ensuring good sleep habits.

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Dr. Schär Institute