Understanding SIBO: Key Concepts for Nutrition Professionals

Small intestinal bacterial overgrowth (SIBO) is, as the name suggests, characterised by an abnormal growth of bacteria in the small intestine. It is a form of dysbiosis. Symptoms of SIBO tend to be non-specific and may include bloating, abdominal distension, abdominal pain or discomfort, diarrhoea, fatigue, and weakness. It is often blamed as the cause of chronic diarrhoea and malabsorption.

SIBO can be caused by structural abnormalities, motility disorders, or conditions that compromise the immune system. Common risk factors include diabetes, Crohn's disease, and a history of abdominal surgery.

While nutrition professionals cannot diagnose SIBO, understanding the diagnostic process is crucial. The hydrogen breath test is commonly used, where elevated hydrogen or methane levels after consuming a sugar solution indicate bacterial overgrowth.

Elevated blood folate and lower vitamin B12 levels may also be observed in individuals with SIBO. Additionally, due to the imbalance of bacteria in the gut, other nutrient deficiencies or discrepancies may also be observed.

Dietary Management for SIBO:

A key step for someone with SIBO is to identify which foods may be leading to the increase in unwanted bacteria and exacerbating symptoms. A short elimination diet, followed by the gradual reintroduction of these foods, may help to discover this. You’ll learn more about this later in your training.

Some individuals have found that following a low FODMAP diet can help manage symptoms. However, as you will learn later, there are risks associated with a low FODMAP diet, and it is not suitable for everyone.

Ensuring that individuals get sufficient intakes of essential vitamins and minerals is also important, especially if malabsorption is an issue. Probiotics, prebiotics, postbiotics, and synbiotics may also help to limit the growth of unwanted gut bacteria and support the growth of beneficial gut bacteria.

References:

• Bacterial Overgrowth Test. NHS Royal Free London.
• Remote Monitoring of Patients with SIBO, IBS, and Food Intolerances. NHS England.
• Epidemiology of small intestinal bacterial overgrowth. Efremova et al., 2023. World J Gastroenterol.
• Small intestinal bacterial overgrowth: current update. Zafar, Jimenez, and Schneider, 2923. Curr Opin Gastroenterol.
• AGA Clinical Practice Update on Small Intestinal Bacterial Overgrowth: Expert Review. Quigley, Murray, and Pimentel, 2020. Gastroenterology.
• Probiotics, prebiotics & synbiotics in small intestinal bacterial overgrowth: opening up a new therapeutic horizon! Chen and Quigley, 2014. Indian J Med Res.

Updated on: 26/10/2026