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SIBO – an in-depth update

With SIBO appearing more prevalent and discussion around testing methods, Nutritional Therapist, Adrienne Benjamin, takes a closer look.

Can you explain what SIBO is?

Small intestinal bacterial overgrowth (SIBO) is an increase in the number and/ or changes in the types of bacteria present in the small intestine (SI). [1]

The official definition is an overgrowth of bacteria in the SI to greater than 100,000 CFU/ml of proximal jejunal aspirate (compared to the normal levels of <10,000 CFU/ml). [2] Often, these bacteria are commensal types, but are in the wrong location, having moved from the colon to the SI – primarily, Gram-negative aerobe and anaerobe species that ferment carbohydrates into gas. [3]

These bacteria then cause structural damage to the SI brush border and affect digestion and absorption of nutrients, thereby, producing further symptoms. [4]

Whilst most SIBO is associated with an excess of hydrogen in the SI, 15 percent of patients are estimated to have methanogenic bacteria in their gut (methane-producing species). [5]


Why do you think it is something that appears to be growing in incidence?

There is limited data regarding the number of healthy people presenting with SIBO and estimates vary greatly from 2.5 percent to 22 percent, depending on the age of the population and the substrate used for the test. [6]

Many experts state that SIBO is more prevalent than previously thought, but link the apparent increase with more accessible testing methods. [7] Quigley (2019) [8] believes this has led to ‘a highly controversial expansion of the spectrum of SIBO’ that may simply be a result of testing those who are sick from ‘disparate disorders’.

 What are the likely signs that a person is experiencing SIBO?

Unlike with IBS studies, most of the studies into SIBO have not used ‘validated symptom questionnaires’ and the most commonly reported symptom is diarrhoea, followed by abdominal pain, then bloating. Other symptoms often relate to nutrient malabsorption, including weight loss due to fat, protein, and carbohydrate malabsorption and vitamin (A, B12, D and E) and mineral (iron) deficiencies. [9]

What are the most common factors that can cause it? Are some people more susceptible than others? Can it be connected to any other health issues?

At its core, the aetiology of SIBO includes lowered stomach acid, pancreatic enzyme, and bile acid secretions, and anatomical changes, including small intestine obstruction, fistula, diverticula and ileocaecal valve insufficiency. A high prevalence of SIBO has also been found in elderly populations, in people with a history of abdominal surgery and/or narcotic use and in those with diabetes mellitus, scleroderma, cirrhosis, exocrine pancreatic insufficiency, IBS, IBD, coeliac disease and a long list of other disorders.  [6,10]

More than a third of individuals with IBS have been shown to have SIBO and the odds of SIBO are increased by nearly five times in those diagnosed with IBS – older age, female gender and IBS-D are key factors to consider. [11] The incidence of SIBO has also been shown to be substantially increased in IBD patients – both in Crohn’s disease and ulcerative colitis. [4]

Compromised motility or transit time is key and is usually caused by anatomical or endocrine changes or by drug usage, such as proton pump inhibitors, which artificially alter the pH level of stomach acid. [12]


From a practitioner point of view, what are the most important considerations to make when assessing if a client has SIBO?

The non-specific clinical presentation and limitations of testing for SIBO can affect the confidence of an accurate diagnosis and the most important and challenging consideration is to identify and correct the underlying causes for the individual client. [13]

Where clients present with severe bloating, abdominal pain, flatulence, diarrhoea or constipation, and particularly if they have been diagnosed with IBS, testing for SIBO should be considered. Studies have particularly pointed to SIBO in IBS-D subtypes. [5]

Other key things to look for include unexplained weight loss and nutritional deficiencies, which can result from malabsorption, severe diarrhoea and reduction in food intake to ease symptoms. [14]

What kind of testing would need to be done?

The major challenge for practitioners in identifying SIBO is the current lack of agreement regarding a gold standard test. [13] Jejunal aspirate was once considered to be the gold standard, but it is invasive and costly, with high potential contamination of the samples. [9]

The response of symptoms to antibiotics has also been suggested as a method for diagnosis of SIBO [6], but hydrogen breath test using lactulose (LBT) as a substrate is the current preferred method, as it is ‘inexpensive, noninvasive, and relatively simple’. [13]

Whilst, glucose has a higher sensitivity and specificity than lactulose, it is mostly absorbed in the proximal small intestine (duodenum and jejenum) and may not detect bacterial overgrowth in the more distal part of the SI (ileum). As a result, while the clinical significance of distal SIBO is still not well-defined, lactulose is considered to be the preferred substrate for SIBO testing. [13]

To further complicate the situation, between 15 per cent and 30 per cent of people do not produce hydrogen and have methane-producing methanogenic microbes in their gut – so the test should always look for both hydrogen and methane. And some test results show neither hydrogen nor methane, potentially due to bacteria producing mainly hydrogen sulphide, which the current tests do not measure. [5,13]

The final confounding factor is that the patient needs to adhere to strict preparation rules to ensure low fasting levels of hydrogen. [13]

In his 2019 review [8], Quigley refers to a new capsule-based technology to measure intraluminal gases, but while we wait for new technology, the lactulose breath test is the best option.


What factors should be included in a protocol when looking to address? This can include dietary, lifestyle, and other factors?

The three main approaches to SIBO cited in the literature are: [1,2,14]

  1. Treatment of the underlying causes.
  2. Treatment of the bacterial overgrowth.
  3. Removal of nutritional deficiencies.

Antibiotics are currently the first-line therapy for addressing SIBO [16] and a number of studies have identified Rifaximin as the best choice for hydrogen-dominant SIBO due to its characteristics (poorly absorbed, with a broad spectrum of activity that includes both aerobic and anaerobic Gram-positive and Gram-negative microorganism). [17]

A combination of rifaximin and neomycin has been identified as more effective in treating methane-producing SIBO. [5]

As FODMAPs are prebiotics for specific microbial species, [18] and one of the key issues with SIBO is carbohydrate malabsorption, a low FODMAPs diet is a key dietary consideration and is effective for symptom improvement in some patients. [19] It should be considered a short-term intervention, as longer-term FODMAP depletion may result in physiological effects on the intestinal bacteria, colonocyte metabolism and altered nutritional status, although an adapted FODMAP diet under the guidance of a practitioner is considered to be suitable for up to 18 months. [20] It is also worth noting that the FODMAPs diet can reduce symptoms, but does not address the underlying causes of SIBO.

Other dietary recommendations include fat restriction when the patient is experiencing fat malabsorption [13] and consideration of an elemental or formula diet to personalise the nutrient composition to the individual and potentially support bile acid secretion and immunoglobulin secretion. [14]

Stress management is also a major consideration as stress impacts the physiological function of the gut and may affect gut motility, secretions, visceral sensitivity, mucosal blood flow, the composition of the gut microbiota and paracellular permeability. There is also evidence that stress can lead to ‘increased adhesion and translocation of bacteria’. [21]

Supplement wise, what are your recommendations for those with SIBO?

Whilst the research is currently limited, there are some studies supporting the use of natural supplements for SIBO and herbal therapy has been shown to be as effective as antibiotic therapy. [22] The antimicrobial herbs recommended for SIBO include garlic, berberine and oregano.

A recent meta-analysis of evidence relating to the use of probiotics for SIBO concluded that ‘the treatment efficacy of probiotics was remarkable’ and comparable to results achieved with antibiotics but without the potential side effects. Whilst probiotics have not been shown to prevent SIBO and low doses may not be effective, the results indicate that probiotics should be part of a SIBO supplement protocol. [23]

Prokinetic agents have been suggested to support motility1 and pancreatic and other digestive enzymes should be considered, particularly where there is evidence of fat malabsorption6 and in the case of weight loss when a strategy for achieving and maintaining a healthy weight should be considered. [14]

Finally, vitamin and mineral levels should be checked in case of deficiency due to malabsorption, particularly vitamin B12, fat-soluble vitamins A, D and E (in cases of fat malabsorption) and calcium, magnesium and iron. [1,9]


Can SIBO cause any long-term issues if not dealt with?

It has been suggested that SIBO may ultimately lead to intestinal failure, although the long-term prognosis of SIBO is primarily determined by the underlying disease that caused it. A high rate of relapse has also been reported and this is further linked to older age, appendectomy and long-term use of proton pump inhibitors. [2]

Adrienne Benjamin

Nutritional Therapist and NLP Practitioner, having completed her Nutritional Therapy degree at CNELM in 2013. Prior to studying nutrition, Adrienne achieved a degree in business and an MBA and had more than 12 years of experience working in the media industry in senior marketing positions. Adrienne is now Marketing Manager and Nutritionist at ProVen Probiotics.

For reference, please visit:

[1] Dukowicz AC, Lacy BE & Levine GM (2007) Small Intestinal Bacterial Overgrowth: A Comprehensive Review Gasterenterol Hepatol 3(2):112-122

[2] Bures J et al (2010) Small intestinal bacterial overgrowth syndrome World J Gastroenterol 16(24):2978-2990

[3] Pyleris E et al (2012) The Prevalence of Overgrowth by Aerobic Bacteria in the Small Intestine by Small Bowel Culture: Relationship with Irritable Bowel Syndrome Dig Dis Sci 57:1321-1329

[4] Shah A et al (2019) Systematic Review with meta-analysis: the prevalence of small intestinal bacterial overgrowth in inflammatory bowel disease Aliment Pharmacol Ther 49:624-635

[5] Ghoshal UD, Srivastava D (2014) Irritable bowel syndrome and small intestinal bacterial overgrowth: Meaningful association or unnecessary hype World J Gastroenterol 20(10):2482-2491

[6] Salem A & Ronald BC (2014) Small Intestinal Bacterial Overgrowth (SIBO) J Gastroint Dig Syst 4:225

[7] Dukowicz AC, Lacy BE & Levine GM (2007) Small Intestinal Bacterial Overgrowth: A Comprehensive Review Gasterenterol Hepatol 3(2):112-122

[8] Quigley EMM (2019) The Spectrum of Small Intestinal Bacterial Overgrowth (SIBO) Curr Gastroenterol Rep

[9] Grace, E et al (2013) Review article: small intestinal bacterial overgrowth – prevalence, clinical features, current and developing diagnostic tests, and treatment Aliment Pharmacol Ther 38:674-688

[10] Choung RS et al (2011) Clinical predictors of small intestinal bacterial overgrowth by duodenal aspirate culture Aliment Pharmacol Ther 33:1059-1067

[11] Chen B et al (2017) Prevalence and predictors of small intestinal bacterial overgrowth in irritable bowel syndrome: a systemic review and meta-analysis. J Gastroenterol

[12] Su T et al (2018) Meta-analysis: proton pump inhibitors moderately increase the risk of small intestinal bacterial overgrowth J of Gastroenterol 53(1):27-36

[13] Adike A & DiBaise JK (2017) Small Intestinal Bacterial Overgrowth – Nutritional Implications, Diagnosis, and Management Gastroenterol Clin N Am

[14] Gewecke K, Nannen-Ottens S (2017) Bacterial overgrowth: nutrition as part of the therapeutic concept Ernahrungs Umschau 64(4):67-73; 64(5):74-78

[15] Chen WC & Quigley EMM (2014) Probiotics, prebiotics & synbiotics in small intestinal bacterial overgrowth: Opening up a new therapeutic horizon! Indian J Med Res 140(5):582-584

[16] Shah SC et al (2013) Meta-analysis: antibiotic therapy for small intestinal bacterial overgrowth Aliment Pharmacol Ther 2013 28:925-934

[17] Gatta L & Scarpignato C (2017) Systematic review with meta-analysis: rifaximin is effective and safe for the treatment of small intestine bacterial overgrowth Aliment Pharmacol Ther 45:604-616

[18] McIntosh K et al (2016) FODMAPs alter symptoms and the metabolome of patients with IBS: a randomised controlled trial Gut 0 :1-11

[19] Magge S & Lembo A (2012) Low-FODMAP Diet for Treatment of Irritable Bowel Syndrome Gastroenterol Hepatol 8(11):739-745

[20] Altobelli E et al (2017) Low-FODMAP Diet Improves Irritable Bowel Syndrome Symptoms: A Meta-Analysis Nutrients 9:940; doi:10.3390/nu9090940

[21] Konturek PC, Brzozowski T, Konturek SJ (2011) Stress and the gut: Pathophysiology, clinical consequences, diagnostic approach and treatment options J Physiol Pharmacol 62(6):591-599

[22] Chedid V et al Herbal Therapy Is Equivalent to Rifaximin for the Treatment of Small Intestinal Bacterial Overgrowth Global Adv Health Med 3(3):16-24

[23] Zhong C et al (2017) Probiotics for Preventing and Treating Small Intestinal Bacterial Overgrowth: A Meta-Analysis and Systematic Review of Current Evidence J Clin Gastroenterol 51:300-311

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