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I can’t quite believe this myself – but this article was written and scheduled in my posts two whole weeks BEFORE Dr Christianson’s recent article (which has created a bit of a storm in the Functional Medicine world) came out questioning whether SIBO is even a real condition.

The article below, therefore, is not a direct response to his article – and yet it does (eerily) directly address a couple of his points – most notably the thrust of his argument which seems to revolve around the dependability (or lack of) of SIBO tests. This entire post is a deep dive into why we can, and how we do, trust the SIBO testing – and what the experienced and qualified professionals actually do with the results.

The irony, as with everything, is that there are elements of truth to Dr Christianson’s arguments. I will write a more complete and nuanced response to his article in due course. However, as with so many health blogs, his complete disregard of how practitioners actually use the data we glean – and his complete ignorance of the rational and holistic way that we, within the Functional Medicine community, INCORPORATE an understanding of SIBO into the complete care of a patient – leaves many patients confused. He has woefully misrepresented how we actually deal with SIBO in practice and the import we place on SIBO within the context of the whole presentation.

I don’t disagree that there are many (patients and practitioners) who get hung up on “my SIBO” as their sole issue and fixated on gut protocols to completely heal themselves. And yet, as I have written many times on this site, just because SIBO has many myths surrounding it that need to be busted (and SIBO is almost always a secondary and not a primary condition) this doesn’t make it ‘not real’, nor does it invalidate the suffering of those who have issues with small intestinal bacterial overgrowth.

Now, onto the rest of my original article – and do sign up to my updates above so you’ll be notified when I post my fuller response to Dr Christianson’s article. I also know that Dr Michael Ruscio is planning what I am sure will be a very evidence-based response to Dr Christianson – so stay tuned to his blog/social media to read his thoughts.


When it comes to Functional Medicine, we’re fairly used to having some of our testing dismissed or rubbished by the conventional medical community. However, with SIBO, even WITHIN the Functional Medical world there’s a host of differing opinions about whether to test, when to test, what medium to test, what substrate to test with and how to interpret the testing.

I regularly get asked about the validity of SIBO testing by those to whom I’ve recommended it. I also regularly find myself debating in my own mind whether I can really justify recommending spending a further £150ish of my clients’ money on re-tests (and re-tests, and more re-tests). And, to top it all, I also know that one person’s ‘weak positive’ on a SIBO test can give rise to inordinate amounts of distressing symptoms, whereas others can be off the scale in terms of gas production and feel nothing whatsoever. Given this, I wonder whether the test itself has value at all when symptom presentation can tell me so much.

But there are many factors about SIBO which warrant testing. And whilst this won’t be a definitive article (because our comprehension and understanding of SIBO and its tests are changing constantly) I thought I’d lay out what we know, what we don’t and my considered opinion on the plethora of tests available for SIBO and whether to take them (or not).




There are the SIBO breath tests, the IBSChek Test (no longer available) and a Hydrogen Sulfide urine test. Most practitioners who are trained in SIBO diagnostics and treatment will opt for the Lactulose Breath Test (more on glucose vs. lactulose later) which makes it the industry standard – and therefore the “gold standard”, if you like (though there is actually a better method – again, covered later).

In reality, Lactulose breath testing has simply been most used and therefore we have most data for this test. I personally use Aerodiagnostics’ SIBO Lactulose Breath Testing – however, there are others (such as Breathtrackers) which are mostly done using the Quintron system. I’ll be honest, I use Aerodiagnostics because their customer service is faultless and the way they validate their samples (and demonstrate what is alveolar (lung) air and what may be ambient air and might contaminate the sample/distort the reading) is second to none. Other tests are, admittedly, cheaper and probably as valid.

Providing the test instructions are followed to the letter (and whilst it’s not difficult, people apparently get this wrong a fair bit) then these tests are fairly simple to understand.

After a day of a specific preparation diet which removes all fermentable carbohydrates and many ‘digestively difficult’ foods (and anything which might ‘feed’ any bacteria lurking in the small intestine) patients spend 12 hours fasting (overnight). In the morning (WITHOUT having brushed their teeth) a solution (glucose/lactulose) is drunk after first breathing into a bag to capture a baseline reading of gases (hydrogen and methane) coming from the gut.

Over the next 3 hours (gold standard is 3 hours, not 1 hour nor 2 hours) breath samples are taken every 20 minutes. The solution drunk at the start of this test is a fermentable carbohydrate and feeds any bacteria. If there are bacteria in the small intestine they will feed off the solution and ferment – giving off gases which are picked up in the breath samples. Measuring the quantities of gas given off is how we approximate the quantity of bacteria in the small intestine.

Whilst there will always be some bacteria throughout the GI tract, in the small intestine there shouldn’t be many. This means that values lower than 12 ppm of methane, and rises of less than 20 ppm of hydrogen are seen as normal – whereas higher values or sharper rises are seen as evidence of the presence of too much small intestinal bacteria. Additionally, if combined values (hydrogen plus methane in ppm) rise by over 15 ppm this is classed as positive for combination SIBO – meaning both gases are present in symptomatic amounts and the small intestine is home to too many bacteria that are a mixture of both hydrogen-producers and methane-producers.

It is these values, cut-off points and numerical attributions to positive vs. negative tests that causes a bit of diagnostic controversy. No-one really doubts the efficacy of the testing method (sugars will ferment bacteria and give off gas – that’s just biology) but there are questions about the relevance of gas levels and the numerical cut-off values for diagnosing SIBO.




As with much diagnostic testing, we judge what to categorise as ‘positive’ for gas levels based on what we’ve witnessed and evaluated from previous patients. These figures aren’t arbitrary, therefore (contrary to some statements on the internet). There will be those on the borders, however, who (as with all testing) may be incorrectly categorised as positive or negative by just one part per million.

However, these figures aren’t just based on lots and lots of breath tests from which we calculate averages (this is how the default reference range for blood tests is created). Instead, breath tests have been evaluated by professionals working within gastroenterology and compared to small intestinal endoscopy with culture.

This culturing of some of the solution in the small intestine is truly what would be the ‘gold standard’ for SIBO diagnosis and is completely accurate at showing the level of bacteria present. However, it is an invasive procedure when compared with at-home breath testing. Therefore, correlating the breath tests with the endoscopy tests has led to the conclusion that the breath tests are a good reflection AND they have provided us with the numerical values of positive vs. negative.

A recent North American Consensus paper which conducted the above comparisions actually altered the breath test diagnostic criteria for SIBO to the levels mentioned above. This lowered the bar for positive diagnoses and most industry professionals now work to the new standard. All of which is to say that a) breath testing works well to show us what levels of gases are given off by bacteria in the small intestine and b) we do know through extensive research what levels of gases indicate likely symptom-causing levels of bacteria. And yes, this means that we can be fairly confident with the accuracy and criteria in diagnosing SIBO from breath tests.

Urine tests… they’re a whole separate matter. They’re also not the gold standard so you will find that most practitioners won’t use these. If your practitioner is suggesting that a urinary Organic Acids test can diagnose SIBO, they are wrong.

Then there’s the IBSChek test. This, again, is not the gold standard for SIBO diagnosis and, actually, has been surrounded by sufficient controversy to mean that it’s no longer available. This test was designed for diagnosing diarrhoea-predominant Irritable Bowel Syndrome, of which SIBO can be a leading cause.  However, that does not mean that an IBSChek test was diagnostic for SIBO.

This leaves us with the breath testing – which has been well validated and is really a practitioner’s first point of call should they suspect SIBO in a patient.




If you know anything about testing for SIBO you will be aware that there are two different ‘substrates’ (or solutions) which can be drunk for the testing of gases. Both substrates – glucose or lactulose – feed the bacteria and allow it to ferment. And, providing the machinery used for breath sample analysis is set up to do so, use of either substrate can provide readings for levels of both hydrogen and methane.

So why two substrates? What’s the difference – and is one better?

Historically we were taught that glucose solutions were better for SIBO diagnosis, though the groundswell of opinion has markedly changed in recent years. The reason for this is that glucose is a more quickly absorbed sugar. This means that it is highly specific and really will show us whether there are bacteria in the upper gut. However, it is absorbed before reaching the entire length of the small intestine. As it is much more quickly broken down than Lactulose and doesn’t reach the entire GI tract length, if overgrowth is in the lower portion of the small intestine it may be missed. This is particularly true of patients with slowed gut motility, a common symptom and predisposing factor for SIBO.

Lactulose, by comparison, is a poorly absorbed sugar. In medical circles it is used as a laxative for this very reason (and many patients, both with and without SIBO, report bowel changes after testing due to the laxative properties of lactulose). Using this, the entirety of the GI tract can be mapped, including the large intestine (from approximately the start of the third hour). This is what gives rise to a classic ‘double peak’ picture for those positive for SIBO – where the gases are high in the upper gut (SIBO) and then peak again at the colon – demonstrating normal colonic fermentation because bacteria SHOULD be there.

The downside of lactulose is that it has been reported to have lower specificity. This means that it can give false positives as gases that are given off may be due to the solution’s ability to disrupt the ecosystem of the gut, rather than there being an issue with the gut itself.

All of these testing quirks and anomalies can be judged and assessed by a good practitioner. Those who know what they’re looking for will be able to judge which test is appropriate, which substrate to use – and how to interpret the results, which may be more complicated than you would think.




So, thus far, the testing seems great. Find someone who knows what they’re doing, test, treat – sorted… right?

Well, perhaps. But I have to evaluate many things in my practice, and sometimes finance is one of those. Testing isn’t cheap – and for SIBO there are some classic signs and symptoms which, when reported, automatically put someone in the SIBO realm, as far as my clinical ear can assess. And no, that’s not particularly scientific, but it’s part of what it means to be a modern healthcare practitioner in the Functional space. We use our clinical experience as much (often more) than our data analysis.

When assessing a client with gut dysfunction I am always supremely mindful that every gut symptom can be caused by a myriad of things. Even if I can judge that it is likely a pathogenic, parasitic, overgrowth, dysbiotic or fungal issue – actually knowing precisely what is happening is almost impossible simply from clinic symptom analysis.

For this reason, I typically like to see comprehensive gut testing on each of my patients. It rules out a lot of things that even the best nutrition/diet cannot ‘fix’. It also eliminates (or highlights) the possibility of there being a gut component for my patients’ systemic symptoms. This test is something that I like IN ADDITION to any small intestinal mapping through SIBO testing.

These large intestine tests aren’t cheap, however – and if I find something in a stool test I am aware that there is a high likelihood that whatever I need to treat will be done using roughly similar agents as would be used within a SIBO protocol.

Again, this may seem highly unscientific, but that’s the miracle of herbal protocols and Functional Medicine treatments – particularly those which emanate from a Naturopathic perspective, as mine do. There are many, many ways to treat conditions – but a lot of the ways to treat one condition also double up to treat other conditions.

Selection of the best protocols is a combination of tests AND clinical expertise which allows you to judge the right approach for your patients.

This means that if a SIBO test on top of a stool test (and other blood chemistries) is a bridge too far (financially) – then it is not always necessary, particularly if other things get flagged up on the stool test. Any protocol that I construct (for a patient like this who reports with classic SIBO symptoms) can include some antimicrobials that work equally well for SIBO as other gut pathogens/overgrowths.

That said, there is a huge benefit to pre-treatment testing: judging progress. If you have read about SIBO at all you will know that it is sometimes reported as difficult to treat. In truth, it can be tricky – but it’s more accurate to state that it can take a lot longer than people think, particularly if no ‘root cause’ has been identified. (I wrote about the myth of SIBO relapse here.)

Having a test which shows you the numerical values present before you start the first round of treatment can be useful to assess how far you’ve come after treatment. Symptomatic relief can be poorly correlated with gas reductions in SIBO and this can leave patients feeling discouraged and losing faith mid-way through treatment if multiple rounds are required. Having decreasing lab values can, and regularly does, provide the positivity needed to help patients stay the course and be encouraged that they are moving in the right direction.




But this latter discussion point highlights an important consideration for SIBO: the endless re-testing. To judge improvements you are meant to re-test relatively swiftly after the completion of each round of antibiotics/antimicrobials. With some patients taking multiple rounds to clear this can prove expensive.

Here again is where clinician experience and patient-reported symptoms are vital. If you have experienced a complete remission of symptoms, there is the possibility of not re-testing. Some would say this is negligent and you really need to make sure that the SIBO is gone completely otherwise it could recur within weeks. However, others would contend that re-testing when you feel that much better is a waste of money and time, whilst also potentially risking SIBO recurrence simply by taking a concentrated Lactulose solution.

Which side of the argument you fall down on depends on many factors – mostly down to the patients. Many want to see their re-tests, just to prove to themselves that they’re free of the SIBO. Many want to avoid the situations of recurrent SIBO they’ve read about online (for why that’s mostly mythical and not always true, check out my post here). But it isn’t, as some practitioners would have you believe, absolutely necessary. Nor is it always useful – because sometimes a positive result can coincide with someone feeling absolutely symptom-free. In these situations, pursuing further treatment rounds can prove taxing and unnecessary.




I can be very flexible as a practitioner when it comes to re-testing. Many of my clients like to see how things go, continuing with prokinetics after treatment whilst they try to work out how they feel rather than immediately retesting.

And yet I would stop a patient doing endless re-tests if we have conducted a test which ordinarily would be classed (according to the criteria above) as positive… and yet they are asymptomatic. Because if this is the case it is likely not going to benefit them to treat further.

This has happened on several occasions in my clinic. It creates a negative association for the patient when they feel fine and without the bloating/distention/bowel issues they used to experience – but they are aiming for a specific lab value because they know that’s what ‘negative’ means (less than 12 ppm methane, less than 20 ppm rise of hydrogen) and their gases are higher than that. Chasing the lab value or ‘normal’ can prove impossible… and moreover, it’s not actually necessary if the patient is, to all intents and purposes, better.

This is a difficult area, particularly as Functional Medicine gains credibility by utilising complex scientific diagnostics which are designed to validate our diagnoses and methodology. However, I have said before – when it comes to the gut, patients must be treated according to their symptoms, not according to their lab values.

This may not be true of vitamin levels in the blood or cardiovascular markers, but these are largely asymptomatic. The gut, however, is a set of organs which is utterly individual for each person. This means that there are no ‘optimal ranges’, really. There’s just our best guess at what feels OK.

And, if you read my blog last week, then ‘what feels OK’ is sometimes the best marker of wellbeing. In Functional Medicine, we treat when there are symptomatic challenges based on our understanding of systems biology. But we are also guilty of over-treating with our pills and potions, chasing down lab values rather than listening to the stories of our patients.

Now, this doesn’t mean that I am only listening to gut symptoms to judge whether there is further to go with gut treatment. As the impact of gut issues can literally manifest anywhere on the body I have to be mindful that sometimes gastrointestinally feeling ‘better’ doesn’t actually mean we’ve resolved the issue – just that compared to what that patient has felt, their current symptoms are minor. I will always ensure to ask more broadly – about sleep, anxiety, skin health, food activities etc. to assess whether a gut situation is resolved.




Therefore, as I conclude yet another really long article on the vagaries and diagnostics of SIBO, I hope that even if you’ve barely skimmed this article the length of it highlights something very important: SIBO is not able to be summed up in a short blog post which laments its tricky prognosis and challenging treatment. Nor can it be dismissed by conventional medicine as ‘nonsense’ (and I’ve lost count of how many breath tests have been dismissed by doctors as such).

Instead, there is a lot of science here. A practitioner’s job is to put in the effort to understand it and then apply it, whilst also bearing in mind the finances and the requirements of the patients. However, in this internet wilderness filled with citizen scientists and seemingly endless ‘Summits’ which often just add streams of confusing data into the mix, I hope that this blog post can prove useful to clear up yet more myths about gut treatment and the diagnosis of Small Intestinal Bacterial Overgrowth.


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