SIBO vs IBS: What’s the Difference and Why It Matters
By Joana Amram — Registered Nutritional Therapist (ANP/APENB), CNM London Gut health, IBS & SIBO · Lisbon & online · joana-amram.com
If you live with bloating, gas, or unpredictable digestion, you may have been told you have IBS — Irritable Bowel Syndrome. What many people aren't told is that a large share of IBS cases may actually be linked to something more specific: SIBO, or Small Intestinal Bacterial Overgrowth.
Understanding the difference is often the turning point. It's the difference between managing symptoms forever and finally asking why they're happening.
What IBS actually means
IBS is a functional digestive condition. That means it's identified by its symptoms rather than by a clear, measurable cause. Common patterns include bloating, abdominal pain, diarrhoea, constipation (or both), and shifting bowel habits.
Here's the part that matters: IBS is often a "catch-all" label, given when no obvious cause has been found. It describes what you're experiencing — not why.
What SIBO is
SIBO happens when bacteria overgrow in the small intestine, where they don't belong in large numbers. As they ferment food, they produce gas, and that drives a lot of the bloating and discomfort people feel. Unlike IBS, SIBO has a specific underlying mechanism — and it can often be identified through breath testing.
The key differences
The simplest way to hold it in your head: IBS is usually labelled without a clear root cause and identified by symptoms, with care focused on managing those symptoms. SIBO is commonly associated with a measurable bacterial overgrowth, can be tested for, and allows a root-cause approach when properly addressed.
Can "IBS" actually be SIBO?
This isn't a fringe idea. A large systematic review and meta-analysis of 50 studies (over 8,000 IBS patients) found that around 38% of people with IBS tested positive for SIBO, and that those with IBS were nearly five times more likely to have SIBO than healthy controls [1]. In other words, more than one in three "IBS" cases may have an identifiable overgrowth sitting underneath the label.
This is often why people try diet after diet, take supplement after supplement, and still don't get lasting results. When the root cause isn't addressed, symptoms tend to come back.
If this sounds like your story, you're not imagining it — and you're not out of options. If "IBS" has been your label but nothing's worked, here's my deeper take on why standard IBS advice so often fails.
Why they're so easily confused
SIBO and IBS share a lot of ground: bloating (especially after eating), gas and visible distension, abdominal discomfort, new food sensitivities, and irregular bowel movements. Because the symptoms overlap so heavily, SIBO is often missed.
If bloating after meals is your main struggle, you may find my post on why you're always bloated after eating helpful too.
What's often underneath the symptoms
Even when the label is "IBS," the symptoms frequently trace back to deeper patterns, such as: sluggish gut motility, chronic stress and a dysregulated nervous system, low stomach acid, microbiome imbalances, or environmental factors like mould exposure.
One of the most well-documented triggers is a previous gut infection. A meta-analysis of 47 studies (over 28,000 people) found that around 1 in 7 people who experience acute gastroenteritis go on to develop post-infectious IBS — and were more than four times as likely to develop it as those who hadn't been infected [2]. A bout of food poisoning years ago can genuinely be where today's symptoms began.
This is the layer most "IBS" advice never reaches — and it's where lasting change usually starts.
Why a personalised approach matters
Whether you've been told it's IBS or you suspect SIBO, the path forward is the same: identify your unique root cause. There's no single diet or supplement that works for everyone. A personalised approach looks at your specific symptoms, your history, your lifestyle, and your individual triggers — and works alongside your doctor, not instead of them.
When it might be time to look deeper
If you've been dealing with chronic bloating, ongoing digestive discomfort, or an "IBS" label that simply doesn't improve, it may be time to look beneath the symptoms.
This is exactly the work I do with clients — finding and supporting the underlying drivers of SIBO and gut issues, one person at a time.
Curious whether SIBO could be behind your symptoms? Let's talk it through — no cost, no obligation.
Book your free 15-minute call →
A quick closing thought
IBS is often a label. SIBO may be one of the causes hiding underneath it. Understanding the difference can be the moment everything shifts — from managing symptoms on repeat, to actually addressing the root of what's going on.
This article is for educational purposes and is not medical advice. Always work with your doctor for diagnosis and before making changes to your care.
Frequently asked questions
Is SIBO the same as IBS?
No. IBS is a symptom-based label, while SIBO refers to a specific bacterial overgrowth in the small intestine that can be tested for. Research suggests around a third of IBS cases may have underlying SIBO.
Can you have SIBO and still be told you have IBS?
Yes. Because the symptoms overlap so much — bloating, gas, irregular digestion — SIBO is frequently missed, and people are given an IBS label instead.
Why do my gut symptoms keep coming back?
When the underlying root cause isn't addressed, symptoms tend to return even after diets or supplements. Identifying what's driving the symptoms is usually the key to lasting relief.
Can I work with you online if I'm not in Lisbon?
Yes. I support clients online in English, Portuguese, Spanish and French, as well as in person in Lisbon and Estoril.
Related reading
– IBS: Why Nothing Has Worked & What to Do Instead
– Why Am I Always Bloated After Eating?
References
Shah A, et al. Prevalence and predictors of SIBO in IBS: a systematic review and meta-analysis. Am J Gastroenterol, 2020. pubmed.ncbi.nlm.nih.gov/29761234
Porcari S, et al. Prevalence of IBS and functional dyspepsia after acute gastroenteritis. Gut, 2024. pmc.ncbi.nlm.nih.gov/articles/PMC8144546