SIBO: the test is easy to fail, and most people who 'have it' have something more treatable.

True bacterial overgrowth needs a reason: a blockage or a gut that has stopped moving. Most people with a positive breath test have neither.

This page is about understanding the condition and the role the brain and nervous system can play in it. It is not a diagnosis. Your own clinicians know your case.

What SIBO is

The small intestine is a five-metre tube between the stomach and the large intestine, and it stays relatively low in bacteria because it keeps moving, sweeping contents onward. Small intestinal bacterial overgrowth, SIBO, happens when that sweeping slows and bacteria multiply where they should not, causing bloating, gas, diarrhoea, pain and sometimes poor absorption of nutrients. Real SIBO has a real cause: a partial blockage from scar tissue, inflammation or a tumour, surgery that has changed the plumbing, or a disorder of the gut's nerves and muscles that stops it contracting properly.

SIBO is usually diagnosed with a breath test, in which you drink a sugar solution and the hydrogen or methane produced by bacteria is measured in your breath. The test is simple and widely available, and that is part of the problem. It is prone to false positives: healthy people with no overgrowth regularly test positive, particularly with the lactulose version, and there is no agreed cut-off.

So a positive result lands on a lot of people who have none of the mechanical reasons for overgrowth. They have bloating, pain and altered bowel habit, a normal gut on imaging and endoscopy, and a positive breath test. The ATNS Index of Neuroplastic Symptoms argues that most of these people have a different condition altogether.

The neuroplastic contribution

Neuroplastic symptoms are real symptoms produced by learned pathways in the brain and nervous system rather than by ongoing disease in the body. The gut has its own extensive nervous system, wired to the brain in both directions. When the brain's threat system is on high alert, it changes gut movement, sensitivity and secretion directly: cramping, bloating, urgency, nausea and pain can all be produced without any infection, inflammation or overgrowth. The symptoms are genuine. They are not imaginary and not 'all in your head'. And because the pathways are learned, they can change.

The ATNS Index of Neuroplastic Symptoms takes a detailed position on SIBO. It notes that mechanical causes are uncommon and that most people tested do not have them. Instead, they have gut symptoms with no mechanical explanation, which means they actually have a form of irritable bowel syndrome or functional dyspepsia, both of which usually have a strong psychophysiologic contribution. Because the test produces false positives, some of these people get an incorrect positive result and a course of antibiotics. The index observes that this happens regularly because many physicians are unaware of neuroplastic symptoms and are relieved to find an abnormal test that seems to explain the patient's complaints.

The index adds a subtle point. In some people, neuroplastic symptoms are severe enough to genuinely slow the gut. It describes patients from Dr Clarke's practice, one with a paralysed stomach and another with a bowel that moved once a month despite multiple laxatives, whose motility problems resolved completely with mind-body treatment over two to three months. Such patients might well have had a true positive SIBO test, but antibiotics would not have addressed the cause, which was a nervous system shutting the gut down. The index's bottom line: unless a person with a positive test has a mechanical or neuromuscular reason for a slow small bowel, they will most likely respond best to treatment aimed at neuroplastic symptoms. See also gastroparesis and constipation.

What the research shows

A 2024 clinical practice update endorsed by the European and American neurogastroenterology and motility societies offers a critical appraisal of the SIBO hypothesis and breath testing. It describes the serious limitations of breath tests, including a lack of standardisation, variable cut-offs, and the influence of diet, transit time and other gut conditions on results, and cautions against treating a positive breath test as proof of overgrowth in people with functional symptoms. This is as close to a consensus position as the field has.

A 2020 review of SIBO and irritable bowel syndrome reports that lactulose breath testing flagged about 21 percent of healthy controls as positive in one comparison, against 1 percent for direct culture of small bowel fluid, and that an earlier study found lactulose breath testing could not distinguish IBS patients from healthy controls at all. It also notes the real overlap: some people with IBS-type symptoms do have measurable overgrowth, and breath-positive patients respond somewhat better to the antibiotic rifaximin. So the relationship is not zero. It is simply far weaker, and the test far less reliable, than the popularity of the diagnosis suggests.

A 2017 review describes SIBO and IBS as a bridge between the functional and organic, acknowledging that estimates of overgrowth in IBS vary enormously between studies depending on the test used. Honest summary: a positive breath test in a person with no mechanical cause is weak evidence of overgrowth, strong evidence of a functional gut disorder, and functional gut disorders are the conditions in which the brain-gut contribution is best established.

Signs the brain may be part of the picture

• You have no surgery, stricture, Crohn's disease, scleroderma, diabetes-related nerve damage or other reason for a slow small bowel.
• Endoscopy, imaging and blood tests are normal.
• Antibiotics helped briefly, or not at all, and the symptoms returned.
• Symptoms track stress, anxiety, travel and sleep more than any particular food.

A solution that addresses it

Pain and symptom reprocessing is an approach built for symptoms generated by the nervous system, and the gut is one of the places it has the longest track record. It combines education about neuroplastic symptoms, somatic tracking (attending to bloating or cramping with curiosity rather than alarm), reducing fear and the sense of threat, a graded return to foods and situations you have been avoiding, emotional awareness and expression, and acceptance and commitment skills. Trained clinicians deliver it, and digital programs now make it more accessible. It works alongside your gastroenterologist's care, not instead of it. Our introduction to ACT explains the acceptance skills.

Cindra is a daily AI companion built around these approaches, with daily check-ins, short practices and plain-language lessons for people whose symptoms have a neuroplastic component. If your SIBO keeps coming back, you can join the waitlist.

What to do next

1. Make sure the mechanical causes have been looked for. Ask your gastroenterologist whether you have any structural or neuromuscular reason for a slow small bowel. Unexplained weight loss, blood in the stool, anaemia, persistent vomiting, fever, or symptoms starting after age 50 need prompt investigation.
2. Treat real SIBO if it is real. If there is a mechanical cause, antibiotics and treatment of the cause are appropriate. Do not stop any prescribed treatment without discussing it.
3. If there is no mechanical cause, change the question. 'Is this IBS or functional dyspepsia with a brain-gut component?' The ATNS index says this is the more likely diagnosis for most people with a positive test.
4. Start retraining the brain-gut connection. Widen your diet in small steps, practise the exercise below, and use pacing rather than restriction as your main tool.

This article is for general education and is not medical advice, and it does not diagnose or treat any condition. Persistent symptoms deserve a proper medical assessment to rule out disease or injury before a neuroplastic explanation is considered. If your symptoms are new, changing, or come with red-flag signs such as fever, unexplained weight loss, numbness or weakness, chest pain, or loss of bladder or bowel control, see a clinician promptly.