SIBO - syptoms, testing treatment | Brighton Dietitian Nutritionist
Brighton based Registered Dietitian Nutritionist.
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SIBO – symptoms, testing and treatment

SIBO test diet IBS immunity

SIBO – symptoms, testing and treatment

Image by congerdesign from Pixabay

I guess you’ve probably heard about SIBO by now? In a world where probiotics are being liberally added to just about everything (probiotic crisps anyone?), there’s understandably mega-interest in whether bacterial dysbiosis (imbalance in the types of bacteria) or overgrowth in our guts could be leading to problematic gut symptoms. 

Let’s take a closer at the SIBO; causes, evidence-based diagnosis and treatment and where we’re at with any special SIBO diets. 

What exactly is SIBO? 

Small intestinal bacterial overgrowth (SIBO) – also referred to sometimes as SBBO (small bowel bacterial overgrowth) is when there is an unusually large amount of bacteria in the small intestine; an area where they don’t typically like to hang out. 

How do they get there then? 

The human body has a number of ways in which it protects against bacterial overgrowth in the small intestine. Besides the pH and general environment down there being particularly inhospitable to unwanted bacteria, the gut is also usually moving pretty constantly; helping food to pass through and absorbing nutrients along they way. Our intestines also replace their ‘lining’ – an epithelial layer which helps to protect us, around every 5-7 days. Neat, huh. 

SIBO testing diagnosis private dietitian Brighton
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Sometimes though, these systems fail. 

The development of SIBO is complex and not entirely understood, but it’s typically linked to chronic conditions that can cause stasis in the gut (when the gut doesn’t move like it should do) like diabetes, use of medications like PPIs that can reduce gastric acid secretion and following surgical interventions. There have also been links found showing increased risk of SIBO for people with systemic sclerosis or inflammatory bowel disease like Crohn’s. There have also been links proposed with coeliac disease.

When these things happen, bacteria which normally can’t get to these parts manage to find their way in and start colonising. 

What are SIBO symptoms? 

Typical symptoms can include: 

  • Abdominal pain
  • Gas 
  • Diarrhoea / constipation
  • Bloating

More serious symptoms can include

  • Malabsorption
  • Vitamin and iron deficiency
  • Weight loss

Sound familiar? These symptoms can be very similar to other gastrointestinal conditions, that’s why it’s important to work with your GP and dietitian / other gastro specialists to get a proper diagnosis. 

How is it diagnosed? 

There’s no one specific test that’s universally recognised as a validated, gold standard for diagnosing SIBO, but one of the most widely referred to is something called jejeunal aspiration – that involves a tube being inserted through your mouth, into your stomach and through your duodenum into your jejeunem (part of your small intestine). A sample is then taken and depending on what they find, you’ll have your diagnosis – or not. 

The problem with this is that at the moment there’s no standardisation for what type of bacteria they’re looking for, where they find it or the numbers involved to get a diagnosis. 

SIBO symptoms testing dietitian Brighton
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Breath testing

As jejeunal aspiration is expensive, time-consuming and invasive, other less invasive procedures have been extensively researched – including breath testing. Again, this has its limits and the jury’s still out on which breath tests are best for diagnosing SIBO. 

How does the test work? 

Well, our wee human cells simply don’t produce hydrogen or methane gas – and so the presence of it in our breath will come from bacterial fermentation of ingested carbohydrates. This is then metabolised and released via our lungs. 

The procedure itself involves ingesting a set amount of a carbohydrate – usually glucose or lactulose. A breath sample will be taken before ingestion and then at set times afterwards – and the amount of hydrogen and / or methane you excrete in your breath is then measured. 

Hydrogen sulfide testing kits are also being developed – though widely available gas chromatography equipment isn’t currently able to consistently detect hydrogen sulfide. Development of these tests is ongoing and assessment of hydrogen sulfide production may improve sensitivity and specificity of breath tests for SIBO.

Sounds pretty foolproof?

Unfortunately not – there’s more than a few issues with the standardisation of the procedure; what’s being tested for, how long to test, what the results are. 

As there’s no validated, standard test yet, depending on what test you have and where you have the procedure, the cutoffs for how much the test rises and how to do it may all vary. How the results are interpreted for treatment can vary as well. 

As one example – glucose is absorbed early on in the small intestine, and so any hydrogen produced will likely only represent bacteria in the early past of the small intestine, so if the bacteria are knocking about further on – they won’t be accounted for. 

Lactulose, as another example – isn’t well digested by humans and so is thought to show a more complete picture of where bacteria could be overgrowing. One problem with this, however, is that someone with faster gut transit time could show a very different response to another person with a slower gut transit time. 

Other factors involved include colonisation with different types of bacteria that don’t produce hydrogen or methane and that the results may be indicative of other conditions. 

So… not so clear cut! However, when your symptoms have been thoroughly assessed and any sinister causes of your symptoms have been ruled out, a breath test will likely be used to help support a potential SIBO diagnosis.

I have really bad IBS symptoms – could I have SIBO? 

IBS symptoms and SIBO are pretty damn similar and although it’s tricky to say exactly, some research has shown anywhere between 4-64% of IBS sufferers may have SIBO. However, SIBO sufferers likely won’t respond well in the long-term to standard treatments for IBS. 

You’ll usually need to work closely with your GP, gastroenterologist and dietitian to ensure that other causes of your symptoms have been ruled out before a diagnosis of SIBO can be investigated. If you don’t respond well to treatment you’ll also usually be referred back to your gastroenterologist so they can investigate further.


Treatment for SIBO involves getting rid of the unwanted bacteria and ideally treating the underlying condition that’s causing it – though this may not always be possible. Any malnutrition needs to be addressed as well. The overgrowth of bacteria is typically treated with antibiotics – rifaximin is the most widely studied. Recurrence rate with antibiotic treatment is high though, and so multiple courses may be needed. 

Different bacteria also respond differently to different antibiotics, so again – not all is certain here either. Where there is SIBO and IBS happening at the same time, the results in terms of symptom management could also be confused – as there’s some evidence for large bowel bacterial overgrowth in IBS. 

Surely some gut-friendly probiotics are a no-brainer?

SIBO testing symptoms
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The efficacy of different probiotics have been investigated in SIBO but results are not yet significant enough to advise on specific strains or dosage. 

A 2017 meta-analysis and systematic review of research into probiotics for prevention or treatment of SIBO showed that there was a tendency toward improvement in some symptoms in those already diagnosed with SIBO, along with normalisation of hydrogen breath testing. However, there was no evidence to show that probiotics worked as a preventive measure. 

Interestingly, a recent study published in 2019 looking into probiotic therapy for those with SIBO and IBS versus those with IBS alone showed improvement in overall IBS symptoms of those with combined IBS and SIBO – 71.3% compared with 10.6% improvement in IBS symptoms in those with just IBS12. Worth noting is that the results were taken 30 days after the therapy had stopped, showing a potential for extended effect of treatment, though no longer-term follow up was available. 

While many studies have shown probiotics could be effective in normalising hydrogen breath test results, their overall effect on actual symptoms associated with SIBO hasn’t been consistently positive. 

Is there a diet to help cure SIBO symptoms yet? 

You bet there are loads online… but what does the evidence say? Diets proposed for the treatment of SIBO include the low FODMAP diet, specific carbohydrate diet and the elemental diet. Theoretically these diets should reduce availability of fermentable carbohydrates and so ‘starve’ out the bacteria. 

Though there has been some interesting results from trials of these diets – where symptoms improved and breath-tests normalised for some people; they’re very restrictive, difficult to stick to and their long-term effectiveness in SIBO isn’t clear, recurrence rate remains high.

IBS SIBO breath test symptoms
Photo by Toa Heftiba on Unsplash

Unfortunately, there is no research currently available that shows whether any of these diets are effective in treating any underlying cause of SIBO; and so we can’t make any evidence-based recommendations around any particular type or duration of diet. 

The takeaway 

SIBO is a very real condition and can significantly affect the health and quality of life of people who are affected by it.

Getting a diagnosis and treatment can take time, but there do appear to be ways that can help – antibiotic treatment is the most recommended and evidence-supported. There are no specific recommendations for probiotics in SIBO at this time, though as research progresses in this area, this might well change.

Although there have been many herbal solutions and dietary interventions touted as being helpful for SIBO – there isn’t any robust research to support these at this time. Plus needlessly restricting your diet may lead to a higher risk of nutrient deficiencies. 

If you have any concerning gut symptoms speak to your GP and dietitian in the first instance. They’ll be best placed to help you get to the bottom of what’s causing your symptoms and help you to manage them.

Blog posts you may also like:

What’s the deal with FODMAPs?
Fermented foods – gut friend or foe?

Want help with managing your IBS? More information about my IBS packages can be found here

Full references available on request

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