Prebiotics, Synbiotics and Postbiotics Defined: What Counts and What Is Marketing
How ISAPP defines prebiotics, synbiotics and postbiotics, related terms such as paraprobiotics and psychobiotics, and which label uses are marketing rather than shown benefit.
Content last updated . This page has not been medically reviewed.
The three definitions
| Term | ISAPP definition, in plain words | What must be shown | Source |
|---|---|---|---|
| Prebiotic | A substrate that host microorganisms use selectively, giving a health benefit | Beneficial health effects must be documented. The 2017 update allows non-carbohydrate substances and body sites other than the gut | [1] |
| Synbiotic | A mixture of live microorganisms and substrate(s) that host microorganisms use selectively, giving a health benefit | A complementary synbiotic must be a probiotic plus a prebiotic. A synergistic one has a substrate designed to be used by the co-administered microorganisms | [2] |
| Postbiotic | A preparation of inanimate microorganisms and/or their components that gives a health benefit | Deliberately inactivated cells, with or without metabolites; the benefit must be confirmed in the target host | [3] |
NCCIH (US) describes prebiotics as nondigestible food components that selectively stimulate desirable microorganisms, and synbiotics as products combining probiotics and prebiotics. [4]
Related terms you will see
ISAPP's postbiotic panel noted that other words have been used for inactivated microorganisms, including paraprobiotics, ghost probiotics, metabiotics, tyndallized probiotics and bacterial lysates. It suggested the field use "postbiotic" where it applies. [3] In the 2021 panel's view, substantially purified metabolites such as butyric acid or lactic acid, and vaccines, are not postbiotics. [3]"Psychobiotic" was defined in a 2013 review as a live organism that, in adequate amounts, gives a health benefit to people with psychiatric illness. [5] That review described preclinical work in rodents and early reports in people with irritable bowel syndrome and depression, and it said results from large placebo-controlled studies were awaited. [5] The sources we read do not give a newer consensus definition; see probiotics, mood and the gut-brain axis.
What counts, and what is marketing
| Claim you may see | Check | Source |
|---|---|---|
| "Fiber is a prebiotic" | Not all dietary fibers are prebiotics. Some foods contain prebiotics, but typically at low levels | [6] |
| "Added fiber plus probiotic equals a synbiotic with extra benefit" | The definition is about the mixture and its documented benefit. Look for a trial of that exact product | [2] |
| "Postbiotic" | Needs inactivated microbial cells or parts and a benefit shown in the target host. The panel expected that using these terms on a food or supplement would require health-claim approval | [3] |
| "Heat-killed probiotic" | The AGA noted such preparations do not meet the strict definition of a probiotic. Whether one counts as a postbiotic depends on documented benefit | [7][3] |
| "Psychobiotic for mood" | Defined in 2013, when large placebo-controlled studies were still awaited | [5] |
| "Natural metabolites, short-chain fatty acids" | Purified metabolites alone are not postbiotics | [3] |
What research shows
- Prebiotics. A 2019 review said glucans and fructans are well proven as prebiotics, and that evidence is building for other substances such as oligomers of mannose, glucose and xylose, pectin, starches, human milk and polyphenols. [8] Details and cautions are on prebiotic fibers.
- Synbiotic and postbiotic products. Proper evidence not found in the sources we read for the benefit of any particular commercial synbiotic or postbiotic product. We searched the ISAPP consensus statements, NCCIH, the NHS probiotics page and the AGA technical review. Both panels discussed existing and required levels of evidence. [2][3]
- Stability. The postbiotic panel notes that concerns about keeping live microbes viable do not apply to postbiotics. [3] That is a manufacturing point, not proof of benefit.
Official intake levels
The sources we read do not describe official recommended intakes for prebiotic, synbiotic or postbiotic products as a group. Fiber targets are on dietary fiber targets.Frequently asked questions
Is a prebiotic the same as a probiotic?
No. A prebiotic is a substrate that host microorganisms use, while a probiotic is a live microorganism. [1][4] For the head-to-head see prebiotics vs probiotics.
Is all fiber a prebiotic?
No. Not all dietary fibers are prebiotics. [6]
What is a synbiotic?
A mixture of live microorganisms and substrate(s) that host microorganisms use selectively, giving a health benefit. [2]
What is a postbiotic, and is it the same as a heat-killed probiotic?
A postbiotic is a preparation of inanimate microorganisms and/or their components that gives a health benefit. [3] A heat-killed probiotic can only be called a postbiotic if the benefit is documented. [3]
Are psychobiotics proven for mood?
The sources we read do not show that. The 2013 review that defined the word described mostly early work and said large placebo-controlled studies were awaited. [5]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Safety and who should ask first
References
- Gibson GR, et al. The ISAPP consensus statement on the definition and scope of prebiotics. Nat Rev Gastroenterol Hepatol. 2017;14(8):491-502. Abstract read 2026-10-22.
- Swanson KS, et al. The ISAPP consensus statement on the definition and scope of synbiotics. Nat Rev Gastroenterol Hepatol. 2020;17(11):687-701. Abstract read 2026-10-22.
- Salminen S, et al. The ISAPP consensus statement on the definition and scope of postbiotics. Nat Rev Gastroenterol Hepatol. 2021;18(9):649-667. Abstract read 2026-10-22; full text read via PubMed Central (PMC8387231).
- NCCIH (US National Center for Complementary and Integrative Health). Probiotics: Usefulness and Safety. Read 2026-10-22.
- Dinan TG, Stanton C, Cryan JF. Psychobiotics: a novel class of psychotropic. Biol Psychiatry. 2013;74(10):720-6. Abstract read 2026-10-22.
- International Scientific Association for Probiotics and Prebiotics (ISAPP). Prebiotics. Read 2026-10-22.
- Preidis GA, et al. AGA Technical Review on the Role of Probiotics in the Management of Gastrointestinal Disorders. Gastroenterology. 2020;159(2):708-738. Full text read via PubMed Central (PMC8018518). Read 2026-10-22.
- Sanders ME, et al. Probiotics and prebiotics in intestinal health and disease: from biology to the clinic. Nat Rev Gastroenterol Hepatol. 2019;16(10):605-616. Abstract read 2026-10-22.
- NHS (UK). Probiotics. Page last reviewed 24 November 2022. Read 2026-10-22.