Ajax Harwood Clinic
Gut bacteria and “dysbiosis”
Dysbiosis is a general term for the mix of bacteria in the gut being different from the usual pattern. The science behind it is real and moving quickly, but it is not yet a diagnosis with an agreed definition or a reliable test — which matters, because a great deal is currently sold on the basis that it is.
Get help straight away if
These are uncommon, but they need same-day care — go to an emergency department, do not wait for an appointment.
Contact us promptly if
Not an emergency, but worth being seen sooner rather than waiting it out.
- Blood in your stool, or black tarry stools
- Losing weight without trying
- A change in your usual bowel habit that has lasted more than a few weeks
- Fever, or being woken at night by bowel symptoms
What usually happens
The honest position is that gut bacteria clearly matter, and that the science is not yet at the point where a test tells you what yours are doing wrong or what to take about it. Those two statements are both true at once.
The microbiome tests sold directly to the public have not been shown to guide treatment. Two samples from the same person can return different results and different advice, and the report will still read with great confidence.
Symptoms that get attributed to dysbiosis usually have a nameable cause worth looking for first — irritable bowel syndrome, coeliac disease, bile acid problems, a medication side effect, or inflammatory bowel disease. Those are findable and treatable, which a general imbalance is not.
Antibiotics do genuinely disturb gut bacteria, and for most people that settles over weeks to months without anything being done about it.
Of the things that reliably influence gut bacteria, eating a wider range of plants and more fibre has by far the best support, and it is free. Probiotics have good evidence in a few specific situations and much weaker evidence as a general measure — so the useful question is whether one helps in your situation, not in general.
At your appointment
We will take the symptoms seriously and look for a specific cause, because the treatable explanations are worth excluding before settling for a general one.
Focused tests where the history points somewhere, rather than a broad panel. If you have already paid for a microbiome report, bring it — we will go through what it can and cannot tell us.
An honest conversation about any supplements you are taking or considering, including what the evidence is in your particular situation.
Practical dietary advice, including how to increase fibre slowly enough that it does not make things worse in the short term.
Should I be tested?
Last reviewed 2026-09-23
Some patients ask us about testing for labels like these, often after reading about them online or hearing about them from a naturopathic doctor. Here is what the evidence actually supports for each.
Small intestinal bacterial overgrowth (SIBO)
SIBO stands for small intestinal bacterial overgrowth. It means too many bacteria are living in the small intestine. This can cause bloating, gas, diarrhea, or poor nutrient absorption. It is more common after certain bowel surgeries, or with conditions that slow gut movement. A breath test is the usual way to check for it. This test is helpful, but not perfect. It can miss some cases and mistakenly flag others. The most accurate test involves sampling fluid from the small intestine, but this is rarely done. Because testing is imperfect, your symptoms and risk factors both matter in this diagnosis.
Tests you may hear about
"Candida overgrowth" / systemic candidiasis
Not a recognized medical diagnosis — here’s what it usually means and what to ask about instead.
You may have heard the term candida overgrowth or systemic yeast as a cause of tiredness, bloating, or brain fog. Candida is a yeast that normally lives in your gut and body. Blood tests for candida antibodies do not diagnose this condition. Studies show these antibodies do not predict who has symptoms. A trial of antifungal treatment for these symptoms did not work better than a placebo in research. This does not mean your symptoms are not real. It means the cause is likely something else, and worth finding.
"Leaky gut syndrome"
Not a recognized medical diagnosis — here’s what it usually means and what to ask about instead.
Leaky gut syndrome is a popular idea that a damaged gut lining lets toxins into the blood, causing many symptoms. The gut lining can genuinely become more permeable in some diseases, like celiac disease. But leaky gut syndrome as its own diagnosis, causing fatigue or brain fog on its own, is not accepted by gut specialists. The tests sold for it, like zonulin blood tests, are not reliable. Studies show these tests often do not measure what they claim to measure. Your symptoms deserve a real explanation. Looking for a specific, treatable gut condition is a better next step.
Intestinal parasites
Gut parasites are tiny bugs that can live in your bowel. They are a real and treatable cause of gut symptoms. They usually come from a clear source. This might be travel, dirty water, or contact with someone who has them. Symptoms include diarrhea that does not go away. You may also have cramping or weight loss. A stool test looks for parasites under a microscope. This test works best when there is a likely source. Testing everyone with vague symptoms rarely finds anything. If you have traveled, or have ongoing diarrhea, this test is worth doing.
Tests you may hear about
Worth asking
- What is the most likely explanation for my symptoms?
- Are the tests I have seen advertised worth doing?
- Would a probiotic help in my situation specifically, and which one?
- How do I add fibre without making the bloating worse?
Curious what your doctor is weighing up? The clinical tool we use for gut bacteria is open to anyone — it is detailed and written for clinicians, and you are welcome to read it.
Open the clinician reference →General health information for Ajax Harwood Clinic patients and the public — not medical advice, and not a substitute for seeing your own doctor. In an emergency call 911.