small intestinal bacterial overgrowth: the full lowdown

what is SIBO?

SIBO stands for small intestinal bacterial overgrowth. This occurs when an unusually high amount of bacteria is found in the small intestine which leads to uncomfortable symptoms in the gut. This can happen there is an overgrowth of bacteria in the small intestine, or when bacteria moves from the large intestine into the small intestine.

SIBO is more likely to occur in situations where changes have occurred in the gut, such as following a gut infection, gut surgery, a blockage or nerve damage in the gut or due to diverticulitis. SIBO has also been identified in 4-78% of those who suffer with IBS, although the relationship between SIBO and IBS isn’t clear (1).

common symptoms:

Stomach pain
Bloating
Gut cramps
Excessive wind
Diarrhoea
Constipation
Indigestion or nausea
Weight loss

It is important to see your doctor to rule out other medical conditions if you suspect that you have SIBO, as there is an overlap between the symptoms of SIBO and other gut issues.

risk factors

Changes in the gut or immune system may increase the risk of SIBO (1).

therefore the risk of SIBO tends to be higher with people who have:

IBS
Coeliac disease
Diverticulitis
Inflammatory bowel disease
Fibromyalgia
Pancreatitis

there can also be a higher risk following:

Stomach or bowel surgery
Use of proton-pump inhibitor (PPI) medication
Use of immune-suppressant medication

how is it diagnosed?

There are issues with accurately diagnosing SIBO.

The most reliable test is to measure the amount of bacteria found in a sample of fluid which is taken from the small intestine (the jejunum to be specific). Unfortunately this test is invasive so it isn’t commonly used as a way of diagnosis (2).

Hydrogen and methane breath tests are more commonly used to diagnose SIBO. These tests work by measuring the amount of hydrogen and/or methane produced after consuming a solution which contains either lactulose or glucose.

However, breath tests are less accurate than testing jejunal fluid and carry a risk of both false positive and false negative results depending on how long digestion takes (gut transit time) (3 – 4).

management options

There are a variety of treatment options available for SIBO, however these vary in terms of reliability. This is also a new area of research, so more studies are needed to investigate these.

The most established treatment for SIBO is a course of antibiotics such as: rifaximin, metronidazole or ciprofloxacin (5).

Probiotics may be a useful in the management of SIBO, but the studies which have investigated this have found mixed results so far (6-7).

A number of changes to the diet have been linked with improving the symptoms of SIBO, but the research into these diets is new and more investigation is needed overall.

An elemental diet may help to reduce the number of harmful bacteria in the small intestine for those with SIBO (7). This diet involves consuming all food in liquid form using specialized supplements which contain protein, carbohydrates and fats which are broken down to their simplest forms.

An elemental diet is a very specific and restrictive diet which requires the use of specific prescribed supplements along with support from a specialist dietitian.

There is some evidence that the low FODMAP diet may help to reduce the risk of SIBO returning after it has been treated with antibiotics (1). See here for more information about the low FODMAP diet. However, this is a short term intervention and carries its own considerations.

The ‘specific carbohydrate diet’ and the GAPS diet are sometimes promoted as a treatment options for SIBO. However, both of these diets are very restrictive and there isn’t good evidence for using either of these in the treatment of SIBO.

It is important not to self-diagnose and follow strict diets, but to seek support from your doctor in order to find the best treatment options for you.

where to find support:

Speak to your GP if you suspect that you might have SIBO.
For additional support your GP can refer you to a dietitian or you can find a private practice dietitian.
You can also book a SIBO test in various private clinics.

references:

Goshal et al. (2017) “Small Intestinal Bacterial Overgrowth and Irritable Bowel Syndrome: A Bridge between Functional Organic Dichotomy”. Gut Liver.15;11(2):196-208.
Aziz et al. (2017) “Small intestinal bacterial overgrowth as a cause for irritable bowel syndrome: guilty or not guilty? Current opinion in gastroenterology”. 33(3):196-202
Yu et al. (2011) “Combined oro-caecal scintigraphy and lactulose hydrogen breath testing demonstrate that breath testing detects oro-caecal transit, not small intestinal bacterial overgrowth in patients with IBS”. Gut. 60(3): 334-40.
Rezaie et al. (2017) “Hydrogen and Methane-Based Breath Testing in Gastrointestinal Disorders: The North American Consensus”. Am J Gastroenterol. 112(5): 775-784
Pimentel et al. (2000) “Eradication of small intestinal bacterial overgrowth reduces symptoms of irritable bowel syndrome. Am J Gastroenterol. 95(12):3503-6.
Soifer (2010) “Comparative clinical efficacy of a probiotic vs. an antibiotic in the treatment of patients with intestinal bacterial overgrowth and chronic abdominal functional distension: a pilot study” Acta Gastroenterol Latinoam. 40(4):323-7.
Rezaie et al. (2016) “How to test and treat small intestinal bacterial overgrowth: an evidence-based approach”. Curr Gastroenterol Rep;18(2):8