Small intestinal bacterial overgrowth
SIBO
The short answer
An overgrowth of bacteria in the small intestine. In practice it is almost never diagnosed by sampling the small intestine. It is diagnosed by a breath test that measures gases produced after a sugar drink, which is a different thing measured at one remove.What is not settled
The distance between the name and the test is the source of most of the disagreement about it. The thresholds that turn a breath result into a diagnosis are set by consensus rather than settled by outcome data, the two common sugar substrates disagree with each other far more often than most people are told, and the third gas is not measured at all by most tests sold.
What it gets confused with
Each of these takes one pair and separates them on what can actually be measured.
- Is it IBS or SIBO?
IBS is a diagnosis of exclusion. SIBO is a test result. That difference explains why people carry both labels, and why the two breath tests disagree.
- Is it SIBO or a food intolerance?
Both produce symptoms after eating, and the timing overlaps more than most pages admit. The useful split is fermentation versus enzyme versus immune.
- Is it SIBO or candida?
One of these has a test that specialists argue about. The other has essentially no accepted test at all. That difference matters more than the symptom lists.
- Is it SIBO or histamine intolerance?
Gut bacteria can produce histamine. That is a real mechanism and a routinely overstated one: shared mechanism is not the same as one causing the other.
- Is it SIBO or MCAS?
The figures linking these two come from specialist clinics, where everyone was referred for being complicated. That inflates any overlap you compute.
- Why the diagnostics here are contested
Not a gap in your reading. Specialists genuinely disagree about the tests, the criteria and in some cases whether a condition exists as described.
How it gets tested
What each test physically measures, and what a negative does not rule out.
- Preparing for a breath test
Every lab publishes its own prep rules and they do not match. A prep failure produces no error message, just a number that looks real.
- Hydrogen sulfide testing
One breath test on the US market measures hydrogen sulfide. No published guideline sets a threshold for what the number means. Both facts matter before you buy.
- Lactulose or glucose breath test
The two common breath tests use different sugars and reach different parts of the gut. Where patients took both, they rarely made the same diagnosis.
- Reading a breath test result
What the published cutoffs are, where they came from, and which gas has no agreed threshold at all. A number is not a verdict.
- Retesting
A second test is only a confirmation if it asks the same question. Change the substrate or the lab and you have a new measurement, not a check on the first.
- Tests that are not SIBO tests
Stool panels, food sensitivity panels and organic acid tests are sold for overgrowth questions. What each measures, and why that differs.
- False positives and false negatives
A positive can come from the colon rather than the small intestine. A negative can mean the gas was never measured. Both errors read as clean results.
What people try
What each intervention is, and how much is behind it.
- Biofilms
Biofilms are real microbiology. The gap between what is established and what is sold as a biofilm protocol is the widest we found anywhere in this niche.
- Elemental formula
A pre-digested liquid formula used as a total food replacement. Real clinical use, real difficulty, and a price most pages do not mention.
- Probiotics
Some clinicians use them here, others argue they make things worse in this specific situation. That disagreement is real and this page does not resolve it.
- Prokinetics
Recurrence is common enough that it shapes how people think here. Prokinetics are the usual answer, and the evidence for that use is thin.
- Rifaximin
What it is, what a two week cash course costs in the US, and what happens when it does not work. The price is the reason most people are reading this.
- What this actually costs
Testing, prescription and repeat rounds, with every figure dated. The prescription cash price is why most people are reading about alternatives at all.
Eating with it
Where the food advice comes from and where it contradicts itself.
- Low FODMAP and low histamine together
Following both lists at once leaves very little food. Here is where they actually conflict, and why the overlap is smaller than it looks.
Where this sits on the site
This page is an index rather than an article. It exists so that a label has one place to start from, and so the 23 pages above are reachable without knowing which section we filed them under. The pages themselves are where the work is.
Common questions
- Is this page a diagnosis of SIBO?
- No. Nothing here can tell you what you have. What these pages do is show you what separates one label from another, what each test can physically measure, and where the published sources disagree, so that the conversation you have with a clinician is a better one.
- What is genuinely unsettled about SIBO?
- The distance between the name and the test is the source of most of the disagreement about it. The thresholds that turn a breath result into a diagnosis are set by consensus rather than settled by outcome data, the two common sugar substrates disagree with each other far more often than most people are told, and the third gas is not measured at all by most tests sold.
Related
- Mast cell activation syndromeA syndrome with two competing sets of diagnostic criteria that do not agree. What each one requires, what that disagreement means for you, and what it overlaps with.
- Histamine intoleranceA proposed reaction to dietary histamine with no agreed confirmatory test. Why the published food lists contradict each other, and what the blood test does and does not show.
- Irritable bowel syndromeIBS is defined by symptom criteria and by ruling other things out, not by a test that confirms it. Why that makes overlapping labels so common.
- Food intoleranceA reproducible reaction to a food that does not use the immune mechanism of an allergy. Which means the common tests are answering a different question.