SIBO or Just Bloating? How to Tell the Difference Before You Test

Georgina Waugh, Clinical Nutritionist (BHSc Nutritional Medicine) · 13 minute read · Updated 6 July 2026

The honest answer to how to tell if you have SIBO is that from symptoms alone, you cannot. Not from how bloated you get after lunch, not from which foods set you off, and not from how big your stomach looks by four in the afternoon.

Most weeks someone sits down opposite me who is bloated most days, has read a great deal about the small intestine, and has already decided the breath test is the next step.

Sometimes it is. More often something more ordinary is sitting underneath, it is cheaper to check, and nobody has looked at it yet.

So before you spend a few hundred dollars, here is what that test actually measures, and what I would want ruled out first.

The short version

• No symptom, and no pattern of symptoms, tells you whether you have SIBO. Bloating certainly does not.
• Bloating at least once a week affects around one in five people in their late thirties and forties, and women report it about twice as often as men.
• A breath test does not look inside your small intestine. It measures gas in your breath after a sugar drink, which is a step removed from what you want to know.
• Which sugar the lab uses changes the answer. On the lactulose version, 62% of people with IBS symptoms test positive, and so do 34% of people without them.
• Two of the likelier explanations are things your GP can check. One of them goes unrecognised in around 80% of the Australians who have it.

Why SIBO is the first thing you find

Type “bloated after eating” into Google and within two pages you are reading about bacteria in the small intestine.

That is not because SIBO is common. It is because SIBO is specific. It has a name, a test and a protocol. “We are not sure yet, let us work through it in order” has none of those, so it loses every time.

Specific feels like progress. That is the trap.

Here is a check you can do yourself. Healthdirect, the national health service, has a page on bloating. It names the regular causes as irritable bowel syndrome, constipation, coeliac disease and food intolerances. SIBO does not appear on it anywhere. Not because Healthdirect is behind the times, but because SIBO sits far further down the order than the internet suggests.

How common bloating actually is

The largest survey of this ran across 26 countries, Australia included, and asked 51,425 people. Just under 18% said they bloat at least once a week. In the 35 to 49 band it was 19.4%, and women reported it roughly twice as often as men.

How many people bloat at least once a week, by age, from 51,425 people across 26 countries including Australia. The two darker bars are the ones you are most likely to be in. Women reported it about twice as often as men. The confidence intervals are all under a percentage point wide, so they are left off the chart. Ballou and colleagues, Gastroenterology, 2023.

That number is useful, and not because it is comforting. Bloating most days is a common human experience, not a rare signal. So the question is rarely “why am I bloated”. It is “which of the ordinary reasons is mine”.

So how do you tell if you have SIBO?

You test. And this is where I have to be straight with you about how good the test is.

It works like this. You drink a measured sugar solution, then breathe into a series of tubes over about two hours. Bacteria fermenting that sugar make hydrogen and methane, some of which crosses into your blood and leaves in your breath. The lab reads the rise. Under the North American Consensus, hydrogen climbing 20 parts per million above your own baseline within 90 minutes counts as positive, and methane counts at 10 parts per million at any point.

Notice what is being measured there. Not bacteria. Not your small intestine. Gas in your breath, and the timing of it.

That gap matters more than it sounds. Monash, whose researchers developed the low FODMAP diet, put the underlying problem plainly: people with IBS commonly believe their bloating is caused by too much gas, and the studies do not support that.

The same question, four different tests, four different answers. Pooled results from 25 studies, 3,192 people with IBS symptoms and 3,320 without. The two rows marked with a star are the ones where the gap between the groups was not statistically significant, and one of them is the lactulose test, which is the version most commonly sold. Culture cut-offs are 1,000 and 100,000 bacteria per millilitre of fluid drawn from the small intestine. Shah and colleagues, American Journal of Gastroenterology, 2020, as tabulated by Kholwadwala and Quigley, 2025.

Read the top row first. On the lactulose breath test, the version most commonly sold, 62.3% of the symptomatic group came back positive, and so did a third of the people who had turned up as controls. The gap between them was not statistically significant. Switch the sugar to glucose and the same question gives 20.7% and 4.4%.

Nothing about the people changed between those rows. Only the test did.

There are two reasons for that, and both are worth knowing.

The first is speed. In one study, 40 people with IBS swallowed lactulose tagged with a tracer so researchers could watch it travel. 63% had a positive breath test at three hours. But at the moment their hydrogen rose, the tracer showed the drink had already reached the large bowel in 88% of them. The gas was real. It was coming from the right place at the wrong speed, which is a fast gut, not an overgrown small intestine.

The second is that there is nothing solid to check the test against. The same panel that set those thresholds also voted, 88.9% in favour, that current culture techniques are not good enough to assess SIBO. When 139 patients had both a glucose breath test and a duodenal culture within a week, the two agreed 65.5% of the time. Against culture, the breath test caught 42% of the positives and correctly cleared 84% of the negatives.

So a negative does not clear you, and a positive is right about two times in three, against a yardstick nobody fully trusts.

Australian clinical guidance reached the same place this year. Writing in Australian Prescriber in June, two gastroenterologists put it in one line: overgrowth does occur in some people, but routine testing for it is not of clinical value.

None of this means SIBO is not real. The pooled odds of testing positive are genuinely higher in people with IBS symptoms than in people without. It means the measurement is too unsteady to be the first thing you spend money on.

What is commonly mistaken for SIBO

This is a question people type into Google, and it is the right one to ask.

If your pattern looks like	Ask your GP about	Why it is on the list
Bloating with loose stools, tiredness, or an iron level that keeps drifting down	Coeliac serology: tTG-IgA with either DGP-IgG or a total IgA level, while you are still eating gluten	Coeliac disease affects around 1 in 70 Australians and roughly 80% of them do not know they have it
Bloating that builds through the day, with hard or infrequent stools	Whether you are actually constipated, and what to do about it	One of the four causes Healthdirect names, and the most common reason a stomach visibly changes size over a day
Bloating with wind and cramping that settles and flares in cycles	Whether this fits irritable bowel syndrome	IBS affects at least 3.5% of Australians, and Monash are clear it should not be self-diagnosed
Bloating that follows onion, garlic, wheat, legumes or milk	A short supervised low FODMAP trial rather than a permanent cut	Monash found 3 in 4 people with IBS improve on it and 1 in 4 do not, and designed it to run 2 to 6 weeks, not for life
Bloating alongside heavy periods, breathlessness on stairs, or hair coming out	A full blood count and ferritin	Not a gut problem at all, and it explains more of the tiredness that travels with bloating than most people expect

None of that is me telling you what you have. It is the order I would go in, and almost all of it costs a GP visit rather than a lab fee. Our page on how we work with bloating and gut symptoms lays out the rest.

Two things sit above all of it, and neither is a testing question.

Healthdirect says to see your doctor as soon as possible if bloating comes with diarrhoea, vomiting, severe or ongoing abdominal pain, blood in your stools, a change in your stools, weight loss you were not trying for, loss of appetite, or fever.

Australian Prescriber adds symptoms starting after 50, anything waking you from sleep, pain that is steadily worsening, and a family history of bowel disease, coeliac disease or bowel cancer.

The second is one nobody enjoys writing about, and leaving it out would be worse. Feeling bloated sits on Healthdirect’s list of the most common symptoms of ovarian cancer, alongside feeling full after a small amount of food. That page also says these symptoms are far more often something else, and that what matters is whether they are new or have carried on for more than a few weeks. If that is you, it is a GP appointment, not a breath test.

What I see in clinic. The pattern I meet most often is a woman who has read more about the small intestine than most people ever will, and who has never had a coeliac screen.

She cut bread out about eighteen months ago because it seemed to help a bit. Which means the blood test would probably read normal now whether or not she has coeliac disease, and a straight answer would mean weeks back on gluten, which she is understandably not thrilled about.

Her bloating is also worst in the weeks she is most blocked up. Nobody has asked her about that, including her, because constipation is not a word she would use about herself.

None of the reading was wasted. It just started three steps in.

Before you cut gluten out, read this

This is the part I would most like you to take away, and it costs nothing.

Coeliac disease is one of the four causes Healthdirect names, and Australian Prescriber calls it the great mimic. It affects around 1 in 70 Australians and roughly 80% of them do not know. Your GP can check it with a blood test that has its own Medicare item number.

Here is the catch. That test looks for antibodies your immune system makes in response to gluten. Stop eating gluten and your body stops making them, so the result can come back normal whether or not you have the condition. Coeliac Australia says it plainly: starting a gluten free diet before testing can cause falsely negative and unreliable results.

Undoing that is not a small thing. If you have been off gluten more than about six weeks, you need a gluten challenge: back on a normal gluten-containing diet for at least six weeks before testing, aiming for around 10 grams of gluten a day, which is about four slices of wheat bread. Every day. While feeling however gluten makes you feel.

So the order matters, and it is the reverse of what most people do. Test first, then trial. Not trial, then test.

If you have already stopped, you are not stuck. There is a gene test for the HLA types coeliac disease requires, and it does not care what you have been eating. More than 99% of people with the condition carry one, so a negative result lets you stop wondering. A positive one means little on its own, since around half the population carries them.

And feeling better without bread settles nothing either way. Coeliac Australia is blunt about that: improving on a gluten free diet is not, by itself, evidence of coeliac disease. Wheat carries fermentable carbohydrates as well as gluten, and those upset plenty of people who do not have it.

When a breath test is worth doing

It is worth doing when the answer would change what happens next.

In practice that means the ordinary things have been looked at and have not explained it, and someone will read the result beside the rest of your picture rather than on its own. Preparation counts too: no antibiotics in the four weeks beforehand, the one rule that panel graded highest of all.

If that is where you have landed, our guide to how a SIBO breath test actually works covers the report itself, what SIBO actually is covers the condition, and what an at-home test involves, start to finish answers the practical questions.

One thing worth knowing before you decide. There is no Medicare item number for a SIBO breath test, so the whole cost is yours. Coeliac serology has two of them. The cheaper test, for the more common condition, with the better evidence behind it, is the one most people skip.

What I would not do is start a restrictive diet on the strength of one positive, or take a negative as proof that nothing is going on. Both happen a great deal.

What to do in the next fortnight

The order is the point, and none of this costs anything beyond a GP visit.

1. Start a two-week note tonight. What you ate, roughly when the bloating arrived, and what your bowels did. Two lines a day is plenty.
2. Book the GP and ask for the bloods by name. Australian Prescriber says every new patient with suspected IBS should have a full blood count, C-reactive protein and coeliac serology ordered. That is the list.
3. Keep eating gluten until that blood test is done.
4. Then, and only then, work out whether a breath test would add anything to what you already know.

And before you buy anything, ask yourself:

• Am I bloated every day, or worse on some days than others?
• Has anyone actually asked about my bowels, in the medical sense rather than the polite one?
• Have I had a coeliac test, and was I still eating gluten when I had it?
• What would I do differently on the morning after a positive result?
• Am I trying to find out what is going on, or trying to find something to blame?

That last one is not a criticism. It is the reason most people order a test, mine included, and it is worth naming before you spend the money.

Not sure whether a breath test is your next step?

If you have been bloated for months and cannot work out what to do first, a short call is usually enough to sort the order out. No test is booked on that call.

Book a free 15-minute call

Fifteen minutes, no cost, and you can bring any results you already have.

Common questions

What is commonly mistaken for SIBO?

Constipation, irritable bowel syndrome, coeliac disease and ordinary carbohydrate malabsorption, mostly. Healthdirect names those first four as the regular causes of bloating and does not mention SIBO at all. Fast gut transit is the other one, because it can produce a positive lactulose breath test with no overgrowth present.

What are the first signs of SIBO?

There are none that belong to it alone. Bloating, wind, abdominal discomfort and a change in bowel habit are the usual list, and every one of them is far more often something else. That is why the symptom checklists you find online cannot separate SIBO from the conditions that sit alongside it.

How can I test myself for SIBO?

The collection genuinely is done at home, so in that sense you can. Interpreting it is the harder half. What comes back is a set of gas readings that need reading beside your history, your medications, your bowel habits and how fast things move through you. On its own it is a number rather than an answer.

Where is SIBO pain located?

Usually across the middle and upper abdomen, around and above the navel, because that is where the small intestine sits. But that location is shared with functional dyspepsia, coeliac disease and plain trapped wind, so where it hurts does not tell you what it is. Pain that is severe, new, or wakes you at night should be seen by a doctor rather than tested.

What foods trigger SIBO?

Food does not cause it, although fermentable carbohydrates can make the symptoms louder: onion, garlic, wheat, legumes, some fruits and lactose. Worth knowing that in the 51,425-person survey above, once everything else was accounted for, no food group was independently associated with bloating. Which is a reason to be slow about cutting things out.

What kills SIBO naturally?

This is the most searched question about SIBO and it is the one I will not answer in a general article. Antimicrobial herbs and antibiotics are prescribing decisions that depend on your history, your medications and what the testing actually showed. There is also little point clearing something that comes back if nobody has looked at why it was there. Ask whoever ordered your test what their plan is.

Sources

1. Healthdirect Australia. Bloating. Lists irritable bowel syndrome, constipation, coeliac disease and food intolerances as the regular causes, and gives the symptoms that warrant seeing a doctor promptly.
2. Routine testing for bacterial overgrowth is not of clinical value: Morrison S and Talley N, Diagnosis and management of irritable bowel syndrome, Australian Prescriber 2026;49:93-8. Also the source for the alarm features, the first-line bloods, and Australian IBS prevalence of at least 3.5%.
3. Coeliac Australia. Gluten challenge. At least six weeks back on a normal gluten-containing diet before testing, aiming for about 10 grams of gluten daily, roughly four slices of wheat bread. Coeliac Australia notes there is limited consensus on the exact amount and duration.
4. Coeliac Australia. Testing for coeliac disease. The GP request is tTG-IgA with DGP-IgG (MBS item 71164) or tTG-IgA with a total IgA level (MBS 71163). Serology has a false negative rate of 10 to 15%.
5. Monash University FODMAP. Abdominal bloating versus distension. Bloating is the sensation; distension is a measured increase in girth. Studies do not support excess gas as the cause of bloating in IBS.
6. Monash University FODMAP. About FODMAPs and IBS. Symptoms improve in 3 of 4 people with IBS on the diet and do not improve in 1 of 4; the restriction phase is intended to run 2 to 6 weeks before reintroduction.
7. Barrett JS and Gibson PR, Fructose and lactose testing, Australian Family Physician 2012;41(5). Notes that breath testing carries no Medicare rebate, that an early hydrogen rise after lactulose more likely reflects rapid small intestinal transit, and that glucose is the preferred sugar. Now dated; the journal ceased in 2017.
8. Melbourne Breath Test. Patient FAQs. Confirms Medicare does not cover hydrogen carbohydrate breath tests. A search of the MBS for breath testing returns no matching item.
9. Healthdirect Australia. Ovarian cancer. Feeling bloated is listed among the most common symptoms; new symptoms, or symptoms continuing more than a few weeks, warrant seeing a doctor.
10. Ballou S and colleagues. Prevalence and associated factors of bloating. Gastroenterology, 2023;165(3):647-655. 51,425 people across 26 countries including Australia.
11. Shah A and colleagues. Small intestinal bacterial overgrowth in irritable bowel syndrome: a systematic review and meta-analysis of case-control studies. American Journal of Gastroenterology, 2020;115(2):190-201.
12. Kholwadwala AS, Quigley EMM. Small intestinal bacterial overgrowth and intestinal methanogen overgrowth: are they overdiagnosed? Acta Gastroenterologica Latinoamericana, 2025;55(4):276-291. Table 1 breaks the Shah results down by test method.
13. Yu D, Cheeseman F, Vanner S. Combined oro-caecal scintigraphy and lactulose hydrogen breath testing. Gut, 2011;60(3):334-340.
14. Erdogan A and colleagues. Small intestinal bacterial overgrowth: duodenal aspiration versus glucose breath test. Neurogastroenterology and Motility, 2015;27(4):481-489.
15. Rezaie A and colleagues. Hydrogen and methane-based breath testing in gastrointestinal disorders: the North American Consensus. American Journal of Gastroenterology, 2017;112(5):775-784.
16. Kumar K and colleagues. Lactulose breath testing in healthy subjects before and after probiotic use. Digestive Diseases and Sciences, 2018;63(4):989-995.

Important: This article is general information written by a clinical nutritionist. It is not medical advice and does not replace care from your GP or another qualified health professional. Functional testing does not diagnose, treat, cure or prevent any condition, and results are best interpreted alongside your symptoms, history, medications and supplements.

Written and reviewed by Georgina Waugh

Clinical Nutritionist, BHSc Nutritional Medicine

Last updated: 6 July 2026

Sources reviewed: Australian Prescriber, Healthdirect, Coeliac Australia, Monash FODMAP and the peer-reviewed breath-testing literature