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  • Writer's pictureLucy Pritchard

Are your symptoms IBS or SIBO?

If you have IBS, it’s likely you have heard of SIBO (Small Intestinal Bacterial Overgrowth). According to research, IBS is actually SIBO in up to 78% of cases. So you’ll definitely want to read on to learn about what SIBO is and how it can be diagnosed and treated.

What is SIBO?

Compared to the small intestine, which contains less than 1000 organisms/ml, the large intestine contains greater than 100,000 organisms/ml. In SIBO, there is excessive bacterial growth in the small intestine and a change in the bacteria to the types we would normally see in the large intestine. Let's look at this in more detail.

In the large intestine, the role of the bacteria in part is to feed off carbohydrates. As they ferment the food we eat, they produce gas which provides energy for certain types of bacteria called archaebacteria. These in turn produce methane gas. In SIBO, the small intestine becomes infiltrated with bacteria normally found in the colon. This is an issue as there should be very little gas production in the small intestine. This can interfere with our digestion and lead to a variety of symptoms.

The most common symptoms of SIBO

• Nausea

• Diarrhoea and/or constipation

• Feeling full quickly after eating

• Flatulence

• Distension

• Fatigue and brain fog

• Abdominal pain

In more severe cases, SIBO can lead to micronutrient deficiency (e.g. low iron and vitamin B12).

Who is most at risk of SIBO?

There are multiple factors increasing the risk of SIBO including:

Medication (use of proton pump inhibitors which decrease gastric acid; use of narcotics, which slow gut transit; prolonged antibiotic use)

Diarrhoea-predominant IBS

Prior intestinal resection surgery

Age (advancing age increases the risk)

How is SIBO diagnosed?

Although there is a breath test available to detect for hydrogen and methane, these tests are not 100% reliable. Ultimately it is best to talk to a specialist dietitian to discuss and rule out other conditions (e.g. coeliac disease, Inflammatory Bowel Disease) and food sensitivities as a cause first before considering testing for SIBO.

Can diet eliminate SIBO?

The gold standard treatment is based on the use of antibiotics to eradicate bacterial overgrowth. A few studies have researched dietary management in the treatment of SIBO; however, the studies are of low methodological quality, making it difficult to draw conclusions. At present use of elimination diets including diets that restrict fermentable carbohydrates can be used with direct support and supervision from a specialist. This is essential to minimise the risk of nutritional deficiencies.


Although there are treatments available to eradicate the bacterial overgrowth and reduce symptoms, it’s important to understand the root causes. Successfully treating SIBO requires a specialist approach to the various lifestyle, dietary and pharmacological causes behind the symptoms.


Adike A, DiBaise JK. Small Intestinal Bacterial Overgrowth: Nutritional Implications, Diagnosis, and Management. Gastroenterol Clin North Am. 2018 Mar;47(1):193-208. doi: 10.1016/j.gtc.2017.09.008. Epub 2017 Dec 7. PMID: 29413012.

Pimentel M, Saad RJ, Long MD, Rao SSC. ACG Clinical Guideline: Small Intestinal Bacterial Overgrowth. Am J Gastroenterol. 2020 Feb;115(2):165-178. doi: 10.14309/ajg.0000000000000501. PMID: 32023228.

Souza C, Rocha R, Cotrim HP. Diet and intestinal bacterial overgrowth: Is there evidence? World J Clin Cases. 2022 May 26;10(15):4713-4716. doi: 10.12998/wjcc.v10.i15.4713. PMID: 35801041; PMCID: PMC9198866.

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