SIBO Breath Test
If you’ve ever googled “bloating after everything I eat” you’ll know that SIBO breath tests are having a moment.
On one side: people who’ve finally got an explanation for years of IBS‑type symptoms. On the other: a lot of noise, over‑diagnosis and very expensive supplements.
The truth, as usual, sits somewhere in the middle.
A SIBO (small intestinal bacterial overgrowth) breath test is a non‑invasive way of looking at whether too much fermentation is happening in the small intestine rather than mainly in the colon, where we expect it. That matters because when bacteria are partying in the wrong area of your gut, you’re more likely to see bloating, gas and unpredictable bowels even with fairly normal meals.
You drink a sugar solution (usually lactulose or glucose), then provide breath samples every 15–20 minutes over 90–180 minutes. If hydrogen or methane levels rise earlier or more sharply than expected, it suggests fermentation is happening higher up in the gut. Some people have more hydrogen‑producing bacteria, others have methane‑producing archaea (now described separately as intestinal methanogen overgrowth, IMO). Both can drive similar symptoms, but they often need slightly different treatment approaches, which is why knowing which pattern shows up can be useful.
Because it’s a home test, the process is fairly straightforward: you follow a short preparation period, fast overnight, collect a baseline breath sample, drink the solution, then carry on with timed samples until you’re done. The lab then analyses hydrogen and methane levels and plots them over time. On paper, it looks very clean and objective: a rise of 20 parts per million of hydrogen within 90 minutes is considered positive for SIBO; methane above about 10 parts per million points towards IMO.
But interpeting the test isn't quite so clear cut.
How quickly food moves through your gut (your oro‑caecal transit time) can change how the graph looks. Faster transit can make lactulose tests look positive when the sugar has simply reached the colon early; slower transit can make a genuine overgrowth harder to spot. Some bacteria hardly produce hydrogen or methane at all, which means you can still have symptoms with a negative breath test. This is why you’ll see debates in the research world about over‑diagnosis, under‑diagnosis and how tight the criteria should be.
So is a SIBO test worth doing?
For some people, yes. If you have stubborn bloating, visible distension, gas, discomfort, reactions to higher‑FODMAP meals and IBS‑like symptoms that haven’t shifted with basic changes such as meal rhythm, stress support and gut‑supportive habits, then a breath test can help to make sense of the pattern. It can also be useful if there’s a history of food poisoning, abdominal surgery or long‑term antibiotic or acid‑suppressing medication, as all of these can nudge bacteria into the wrong part of the gut or slow things down.
You won’t be offered this as standard NHS testing. GP investigations quite rightly prioritise ruling out conditions that change medical treatment: coeliac disease, inflammatory bowel disease, cancer and so on. The “gold standard” SIBO diagnosis in a hospital setting would involve taking fluid directly from the small intestine during an endoscopy and culturing it, but that’s invasive, expensive and not practical for routine use. Breath testing wins on practicality, which is why you’re more likely to encounter it in private clinics and within nutritional therapy.
If a test does come back positive, the point isn’t simply “kill the bugs”. We look at:
how to reduce excessive fermentation while still feeding you properly (sometimes that means a carefully managed low FODMAP phase, sometimes it doesn’t)
whether gut motility needs support via hydration, movement, stress management and, where appropriate, prokinetic support
whether low stomach acid, previous infections or structural issues might be contributing
how this all fits with the rest of your picture: bowels, skin, hormones, energy, blood sugar.
We also make a plan for life after SIBO, because long‑term extreme restriction is not the goal. As symptoms settle, gently widening your diet again helps your microbiome and nervous system far more than living in permanent food‑police mode.
None of this replaces your GP. If you’ve had red flag symptoms such as unexplained weight loss, blood in the stool, black or tarry stools, severe ongoing pain, fever, night sweats or vomiting, you need NHS assessment long before you think about private breath tests. And if a SIBO test is positive, it’s still worth keeping your GP in the loop, especially if antibiotics or other medical treatment options are on the table.
If you’re sitting in that grey zone of having been told you've got IBS, you are struggling with ongoing symptoms, your bloods are normal, but you still have no answers” a SIBO breath test can be one of several tools we use to make sense of what your gut is doing.
We’ll always start with the foundations you can influence day to day – things like meal timings, blood sugar balance and nervous system support – and then decide together whether testing adds value or not.
If you’d like a second pair of eyes on your symptoms and you’re wondering whether a SIBO breath test, a comprehensive stool test or simpler changes are the best next step, you’re welcome to book a free introductory call so we can talk it through.