Short answer: probiotics are live microorganisms that confer a health benefit when administered in adequate amounts; prebiotics are substrates selectively used by host microorganisms that confer a health benefit; and postbiotics are preparations of inanimate microorganisms and/or their components that confer a health benefit. Those definitions describe different categories—not interchangeable ingredients or guaranteed outcomes.
Why the distinction matters
These terms often appear together on supplement labels, but each points to something different. Knowing the difference helps you compare products on their actual contents rather than choosing the package with the largest number of “biotic” words.
The International Scientific Association for Probiotics and Prebiotics (ISAPP) maintains consensus definitions for these categories. Its plain-language definitions resource is a useful starting point, while the underlying consensus papers provide the scientific detail.
What is a probiotic?
A probiotic contains live microorganisms. A useful label should identify them precisely, normally by genus, species and strain, and state an amount for the relevant point in shelf life. “Contains live cultures” is not automatically the same as demonstrating a probiotic benefit.
More colony-forming units, or CFU, do not automatically make one product better. Strain identity, dose, formulation, storage and evidence for the intended use all matter. Singapore’s HealthHub advises consumers to follow the individual product’s instructions because timing, storage and use can vary. See HealthHub’s probiotics guidance.
What is a prebiotic?
A prebiotic is not a live microorganism. It is a substrate selectively used by host microorganisms that confers a health benefit. Some dietary fibres may meet this definition, but not every fibre is automatically a prebiotic.
When comparing a supplement, look for the named prebiotic ingredient and the amount per serving. The 2017 ISAPP consensus statement explains why selective utilisation and a demonstrated health benefit are central to the definition; read the prebiotic consensus statement.
What is a postbiotic?
A postbiotic is a preparation of inanimate microorganisms and/or their components that confers a health benefit. “Inanimate” means the microorganisms are no longer alive. The category is not simply another name for any substance produced by bacteria.
The formal definition and its scope are explained in the 2021 ISAPP postbiotic consensus statement. A good product label should identify the preparation clearly enough for you to understand what is actually present.
Can a product contain all three?
Yes. A formula may combine a probiotic, a prebiotic and a postbiotic component. “Tribiotic” is a market term commonly used for that three-part format, but the word itself is not a quality score. Start with the exact strains or preparations, quantities, serving size, storage directions, warnings and evidence.
For a closer look at this format, read What is a tribiotic supplement? You can also browse the Gut Health hub or review how GOPRYME handles evidence on our Science & Standards page.
A practical label checklist
- Identify whether each component is live, a substrate, or an inanimate preparation.
- Look for specific strain or ingredient names, not only category claims.
- Check the amount per serving and whether a live count applies through shelf life.
- Follow the stated storage directions.
- Review sugars, sweeteners, allergens, other ingredients and warnings.
- Be cautious when a category definition is presented as proof of a personal result.
Frequently asked questions
Are fermented foods automatically probiotics?
No. A fermented food is not automatically a probiotic. The microorganisms must be defined and supported for a health benefit at an adequate amount.
Are all fibres prebiotics?
No. A prebiotic must meet the definition, including selective use by host microorganisms and a health benefit.
Do postbiotics contain live bacteria?
No. The consensus definition describes preparations of inanimate microorganisms and/or their components.
This article is educational and does not replace individual medical advice. Check the current product label and consult a qualified healthcare professional when appropriate.