SIBO Ireland: Symptoms, Testing, Diet and the Evidence

SIBO — small intestinal bacterial overgrowth — has become one of the most-searched gut topics in Ireland. This guide explains what the evidence actually says: what SIBO is, how it is tested, what the diet looks like, and the genuinely mixed picture on fibre. It is educational, not a diagnosis or a treatment plan.

SIBO (small intestinal bacterial overgrowth) definition: the presence of excessive numbers of bacteria in the small intestine — where bacterial counts are normally low — producing gastrointestinal symptoms when those bacteria ferment food in the wrong part of the gut.

These are dietary fibre and gut-support products, not treatments for SIBO or any condition. If you have gut symptoms, see a GP first.

What is SIBO?

Small intestinal bacterial overgrowth (SIBO) is defined as an excessive number of bacteria in the small bowel, causing gastrointestinal symptoms.¹ The small intestine normally carries far fewer bacteria than the colon. When numbers rise, bacteria ferment carbohydrates here rather than further down, and that fermentation produces gas.

The bacteria themselves are not unusual — the problem is their location and quantity. This is why SIBO is described as a problem of the gut's "housekeeping", particularly impaired clearance and motility, rather than an infection caught from outside.³

It matters because the symptoms overlap so heavily with irritable bowel syndrome. The AGA Clinical Practice Update (Quigley, Murray and Pimentel, 2020) lists bloating, diarrhoea and abdominal pain as the classic picture.⁴ If you have ongoing gut symptoms, those overlaps are exactly why a doctor's assessment beats guessing.

SIBO symptoms

The symptoms most often linked with SIBO are bloating, excess gas, abdominal pain or discomfort, and changes in bowel habit.⁴ Bloating in particular is the symptom that drives most people to search. We cover that symptom in depth in our guide to probiotics for bloating in Ireland.

One useful distinction is the type of gas produced. Hydrogen-dominant patterns tend to track with diarrhoea and bloating, while methane (now often called intestinal methanogen overgrowth) is more associated with constipation.²

The catch is that none of these symptoms is unique to SIBO. They appear in IBS, in food intolerances, and in several other conditions. Symptoms point to "get this checked", not to a diagnosis.

SIBO testing — and testing in Ireland

The most common, least invasive way to assess SIBO is a hydrogen and methane breath test using glucose or lactulose.² You drink a sugar solution, then breath samples are taken at intervals to measure the gases bacteria produce.

The North American Consensus (Rezaie et al., 2017) sets a hydrogen rise of 20 ppm or more by 90 minutes as positive for SIBO, and methane of 10 ppm or more as methane-positive.² Even so, the ACG guideline is candid that there is no validated gold-standard test, so results are interpreted alongside symptoms by a clinician.¹

In Ireland, breath testing is arranged through your GP, a gastroenterology clinic, or a private testing service — including some mail-order breath-test kits. Start with your GP, who can assess your symptoms, rule out other causes and advise on referral. The HSE advises seeing a GP for persistent digestive symptoms rather than self-managing them.

The SIBO diet and low-FODMAP

There is no single official "SIBO diet". In practice, clinicians most often reach for a low-FODMAP approach, which cuts back fermentable carbohydrates that gut bacteria turn into gas, to ease symptoms while the underlying problem is addressed.

The ACG guideline is clear that dietary evidence for SIBO is limited and approaches should be individualised.¹ The low-FODMAP diet itself is evidence-based for IBS symptoms — Halmos et al. (Monash University, Gastroenterology, 2014) reduced gut symptoms in a randomised crossover trial⁵ — and clinicians extend it to SIBO given the symptom overlap, not as proof it treats SIBO. A low-FODMAP diet is also restrictive and is not meant to be permanent, which is why it is best run with a dietitian who can reintroduce foods properly.

Fibre sits awkwardly inside diet advice, because "more fibre" is generally good gut advice but not always the right move during active SIBO. That is the next section — and it is where the nuance matters. If you are new to the fibre side of gut health, our explainer on probiotics vs prebiotics is a useful primer on what "prebiotic fibre" actually means.

Fibre and SIBO: the honest picture

Here is the part most product pages skip. Fermentable fibre feeds bacteria. In active SIBO, that can mean more gas, not less, which is why some protocols delay higher-fibre intake until after antimicrobial therapy.

The one notable trial on fibre in SIBO is Furnari et al. (2010). It randomised 77 patients with a positive breath test to rifaximin alone or rifaximin plus partially hydrolysed guar gum (PHGG) 5 g/day for 10 days. The combination eradicated SIBO in 87.1% of cases versus 62.1% with the antibiotic alone (per-protocol, P=0.017).³

Read that carefully: PHGG was an add-on to an antibiotic, not a standalone therapy. It is genuinely interesting evidence, but it does not show that taking a fibre powder by itself does anything for SIBO. PHGG is of interest partly because it is a low-FODMAP soluble fibre that is generally well tolerated, dissolves clear and does not thicken — properties that make it gentler than coarse or highly fermentable fibres.

Supplements people search for SIBO

Search data shows people pairing SIBO with berberine, oregano oil, digestive enzymes, Saccharomyces boulardii and others. It is worth being plain: none of these is an established SIBO treatment, and the formal guidelines centre on antibiotics and diet, not supplements.¹

Probiotics are a particular grey area in SIBO — logically they add bacteria, and the evidence is mixed and not guideline-endorsed for SIBO specifically. If you want to understand how probiotics are actually graded by strain and evidence, our guide to clinical probiotics in Ireland sets out the framework.

The honest takeaway: if you suspect SIBO, the highest-value step is a proper assessment, not a basket of supplements bought on the strength of a forum thread. Anything you do add should be discussed with the clinician managing your care.

SIBO in Ireland

If you are in Ireland and think you may have SIBO, the route is straightforward: see your GP first. They can assess your symptoms, exclude other causes, and advise on a hydrogen/methane breath test through a clinic or private service. The HSE advises seeing a GP for persistent or worsening digestive symptoms.

On the retail side, dietary fibre and gut-support supplements sold in Ireland are regulated by the Food Safety Authority of Ireland (FSAI) as food supplements, not medicines.⁶ That means they cannot legally be sold as treatments for SIBO or any disease, and any product claiming to "cure SIBO" should be treated with caution. VAT on supplements in Ireland is 13.5%.

Healthy Origins Natural Healthy Fiber ships from Dublin with tracked Irish delivery and no customs charge, including for orders after 1 July 2026, because it dispatches from within Ireland.

A realistic path, not a quick fix

Frequently asked questions

What is SIBO?

SIBO stands for small intestinal bacterial overgrowth. The ACG clinical guideline (Pimentel et al., Am J Gastroenterol, 2020, PMID 32023228) defines it as an excessive number of bacteria in the small bowel, where bacterial counts are normally low, causing gastrointestinal symptoms. The bacteria ferment food in the wrong place, producing gas. SIBO is a recognised medical condition diagnosed and managed by a doctor, not a self-diagnosis.

What are the symptoms of SIBO?

Symptoms traditionally linked to SIBO include bloating, excess gas, abdominal pain or discomfort, and altered bowel habits such as diarrhoea or constipation (Pimentel et al., 2020; Quigley et al., AGA, 2020, PMID 32679220). These symptoms overlap heavily with irritable bowel syndrome (IBS) and other conditions, which is why a breath test and a doctor's assessment are needed rather than guessing from symptoms alone.

What causes SIBO?

SIBO is associated with impaired clearance of the small bowel — for example reduced motility (the 'cleaning wave' that sweeps the gut between meals), structural issues, or low stomach acid. Furnari et al. (2010, PMID 20937045) note that abnormal intestinal clearance is involved in the pathogenesis of SIBO. Because several different underlying problems can lead to it, the cause is established by a clinician, not assumed.

How is SIBO tested in Ireland?

SIBO is most commonly assessed with a hydrogen and methane breath test using glucose or lactulose. The North American Consensus (Rezaie et al., 2017, PMID 28323273) treats a hydrogen rise of 20 ppm or more by 90 minutes as positive for SIBO, and methane of 10 ppm or more as methane-positive. In Ireland, testing is arranged through a GP, gastroenterology clinic or private testing service. Speak to your GP or the HSE about referral and access.

What is a SIBO diet?

There is no single official SIBO diet. In practice, clinicians often use a low-FODMAP approach, which reduces fermentable carbohydrates that gut bacteria ferment into gas, to ease symptoms. The ACG guideline (Pimentel et al., 2020) notes dietary evidence is limited and approaches should be individualised. A low-FODMAP plan is best followed with a dietitian, as it is restrictive and not meant to be permanent.

Does fibre help or worsen SIBO?

It depends on the fibre and the person, and the evidence is mixed. Fermentable fibres and prebiotics can increase gas and may aggravate active SIBO, so some protocols delay high-dose fibre until after antimicrobial therapy. The one notable trial, Furnari et al. (2010, PMID 20937045), used partially hydrolysed guar gum (PHGG) 5 g/day as an add-on to the antibiotic rifaximin, not on its own, and the combination eradicated SIBO in 87.1% of cases versus 62.1% with rifaximin alone. Fibre choices in SIBO should be individualised with a clinician or dietitian.

Can SIBO go away on its own?

SIBO can relapse and is often recurrent because the underlying cause (such as a motility problem) may persist. The ACG guideline lists antibiotics such as rifaximin among treatment options, and emphasises addressing the underlying predisposing condition. Whether SIBO resolves or returns is a clinical question for your doctor, not something to manage alone with supplements.

What happens if SIBO is left untreated?

Untreated SIBO can cause ongoing bloating, gas and altered bowel habits, and in more severe cases interfere with nutrient absorption. Because symptoms overlap with several other conditions, persistent or worsening gut symptoms should be assessed by a GP rather than self-treated. The HSE advises seeing a GP for persistent digestive symptoms.

Is partially hydrolysed guar gum (PHGG) fibre legal and safe to buy in Ireland?

Yes. Partially hydrolysed guar gum (PHGG), sold as Sunfiber, is a soluble dietary fibre regulated as a food and used in food supplements in Ireland under FSAI rules. It is not a medicine and makes no disease claim. Introduce any fibre gradually with plenty of water, and check with a healthcare professional first if you have a diagnosed gut condition or take medication.

Where can I buy low-FODMAP soluble fibre in Ireland?

Probiotic.ie stocks Healthy Origins Natural Healthy Fiber, a 225g unflavoured Sunfiber PHGG powder providing 6.5g of fibre per scoop, priced at €25.95 including 13.5% VAT, or €68.95 for three. It is a low-FODMAP soluble fibre, vegan and non-GMO, dispatched with tracked delivery from Dublin and no customs charge. It is a food supplement, not a treatment for any condition.