If you’re navigating symptoms like bloating, constipation, diarrhoea, or abdominal discomfort and suspect SIBO (Small Intestinal Bacterial Overgrowth), testing can feel confusing fast.
In this post, I want to walk you through the most common SIBO testing options—what works, what doesn’t, and how I approach testing in clinic.
If you’re interested in learning more check out the SIBO series and don’t forget there is a free Ebook download available to go along with this series which can be downloaded here – The Complete Guide To SIBO.
Breath Testing for SIBO: The Clinical Standard
Let’s start with what’s actually practical.
Although aspirate and culture testing is often called the gold standard, it’s not used outside research settings. It’s invasive, expensive, and honestly not relevant for most people trying to get real answers and move forward with treatment.
That’s why in clinical practice, I focus on breath testing—a non-invasive, accessible way to detect bacterial or archaeal overgrowth in the small intestine.
How SIBO Breath Testing Works
Here’s the basic idea:
You fast (typically 12 hours), drink a test sugar, and then breathe into a collection device every 15–20 minutes for a few hours. The machine analyses your breath for hydrogen and methane gas, byproducts that gut microbes release when they ferment the sugar in your small intestine.
If those gases spike early in the test window, it suggests that microbes are present where they shouldn’t be.
Glucose vs Lactulose: Which Is Better?
So the lactulose glucose debate and which one is better?
You are going to get different opinions depending on who you speak to. There are reasons for lactulose being a better sugar to test for SIBO and there are reasons why glucose is better.
Lactulose is a particular sugar that we can’t actually digest. It is a disaccharide which makes its way down to a large bowel where our resident microbiota can ferment the sugar and produce gas. Glucose on the other hand is absorbed in the small bowel. This means that if the bacterial overgrowth is further on down the small intestine then glucose may miss it. This is one reason why many clinicians prefer lactulose over glucose.
On the other hand lactulose tends to increase gut transit time so when you consume it and you’re looking for that spike in the gas that signifies SIBO if it happens a little bit later on – say between the 80 to 100 minute mark – then it could be your large bowel microbiome and not SIBO after all. This is one of the real downsides of lactulose.
Finally fructose can be saved and run as a third test or all three can be used to really rule out suspected SIBO.
In my practice I tend to run lactulose as the primary SIBO breath test and if the results are still a bit unclear (all the symptoms of SIBO are there and the SIBO tests say all is clear) then I might follow it up with fructose. Over the years I’ve seen glucose miss SIBO too many times to count so have dropped it for the most part just to save patients on test cost outlay and hassle.
It really depends on you, your digestive symptoms, how long you’ve been unwell for how much money you are happy to spend and how quickly you want to get better. These are all factors we have to take into account for testing SIBO.
2 comments
Hi Todd, how much are these tests?
I assume it is the same price regardless of the sugar used?
How much fructose will you give if testing with fructose for SIBO?