Prebiotics, probiotics and postbiotics are often grouped together as if they were three versions of the same thing.
This article is part of the AKK Knowledge Centre, our guide hub for gut health, Akkermansia and microbiome research.
They are not.
Each term has a specific scientific meaning.
In simple terms:
- Probiotics are specific live microorganisms with demonstrated health benefits when administered in adequate amounts.
- Prebiotics are substrates selectively used by host microorganisms that confer a health benefit.
- Postbiotics are preparations of inanimate microorganisms and/or their components that confer a health benefit.
The definitions matter because marketing often uses these words much more loosely than microbiome science does.
Key Takeaways
- A probiotic must be alive when administered.
- Not every live bacterium is a probiotic.
- A prebiotic is not simply “fibre”; it must be selectively used by microorganisms and linked to a health benefit.
- A postbiotic is not simply a microbial metabolite or any dead bacterium.
- A fermented food is not automatically a probiotic food.
- Bigger CFU counts do not automatically mean a better probiotic.
- Benefits are specific to the strain, preparation, dose and outcome studied.
What Is a Probiotic?
The established scientific definition is:
Live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.
There are several important parts to that definition.
The microorganism must be:
- alive,
- adequately identified,
- delivered in an appropriate amount,
- safe for its intended use,
- and supported by evidence of a health benefit.
This means:
live bacteria ≠ automatically probiotic.
A yoghurt containing live cultures is not necessarily a probiotic product unless the specific organisms meet the evidence criteria.
What Does “Strain-Specific” Mean?
Microbial names have several levels.
For example:
Genus → Species → Strain
Two strains belonging to the same species can have different characteristics.
Therefore, research on one strain should not automatically be used to support another.
This is one of the most important principles in probiotic science.
Does a Higher CFU Count Mean a Better Probiotic?
No.
CFU stands for colony-forming units, a way of estimating viable microorganisms.
Consumers often assume:
50 billion CFU > 10 billion CFU.
That is not necessarily true.
A useful probiotic depends on:
- which strain is used,
- what dose has evidence,
- stability through shelf life,
- and what outcome is being targeted.
A higher number can be meaningless if the strain or dose lacks relevant evidence.
What Is a Prebiotic?
A prebiotic is:
a substrate that is selectively utilised by host microorganisms and confers a health benefit.
Many prebiotics are dietary fibres, but not every fibre is a prebiotic.
Examples of compounds commonly studied as prebiotics include certain:
- inulin-type fructans,
- fructooligosaccharides,
- galactooligosaccharides,
- and other selectively utilised substrates.
The key word is selectively.
The substrate must influence microorganisms in a meaningful way and be associated with a demonstrated benefit.
Is All Fibre Prebiotic?
No.
Dietary fibre is a broad category.
Some fibres:
- increase stool bulk,
- retain water,
- alter transit,
- are fermented by microbes,
- or have several of these properties.
A fibre can support gastrointestinal health without meeting the scientific definition of a prebiotic.
What Is a Postbiotic?
ISAPP defines a postbiotic as:
a preparation of inanimate microorganisms and/or their components that confers a health benefit on the host.
“Inanimate” means the microbial cells are no longer alive.
But the definition does not mean:
any killed bacterium = postbiotic.
A health benefit must be demonstrated for the preparation.
Are Microbial Metabolites Postbiotics?
Not by themselves under the ISAPP definition.
Compounds produced by microorganisms — such as:
- butyrate,
- acetate,
- propionate,
- lactic acid,
- or purified microbial molecules
are not automatically postbiotics.
The inactivated microorganisms or their components must remain part of the preparation.
Why Would Non-Living Microorganisms Have Effects?
Microbial cells contain many structures, including:
- cell walls,
- membrane proteins,
- surface molecules,
- enzymes,
- and other components.
Some of these can interact with host receptors even after the microorganisms are no longer alive.
This is one reason the postbiotic field has expanded rapidly.
What Is a Synbiotic?
A synbiotic combines:
- live microorganisms,
- and substrates selectively used by microorganisms,
in a formulation designed to provide a health benefit.
There are different scientific categories of synbiotics depending on how the components are intended to work together.
A product is not automatically a synbiotic simply because it contains “probiotic + fibre.”
Are Fermented Foods Probiotics?
Not automatically.
Fermented foods are produced through microbial growth and enzymatic conversion of food components.
Examples include:
- yoghurt,
- kimchi,
- kefir,
- sauerkraut,
- miso,
- tempeh.
Some fermented foods contain live microorganisms at the time of consumption.
Others do not.
Even when live microbes are present, the food only qualifies as probiotic if the microorganisms meet the probiotic criteria and the health benefit is demonstrated.
Can a Food Be Both Fermented and Probiotic?
Yes, potentially.
A fermented food can also contain a defined probiotic strain.
But “fermented” and “probiotic” are not synonyms.
Probiotic vs Prebiotic
A simple way to remember:
Probiotic = microorganism
Prebiotic = substrate
The probiotic is the live microbe.
The prebiotic is something certain microorganisms use.
Probiotic vs Postbiotic
Probiotic = live
Postbiotic = intentionally inactivated preparation with demonstrated benefit
Both require evidence of health benefit.
Prebiotic vs Postbiotic
A prebiotic works through selective microbial utilisation.
A postbiotic contains inactivated microbial cells or components.
They are completely different types of intervention.
Which One Is Better for Gut Health?
There is no universal winner.
The useful question is:
What outcome are you trying to achieve, and what evidence exists for this specific product?
For example:
- one probiotic strain may have evidence for a particular digestive outcome,
- a prebiotic may influence bowel function or microbial metabolism,
- a postbiotic may be studied for another outcome.
The label category alone does not tell you which is best.
Can You Take Prebiotics and Probiotics Together?
Often, yes, but tolerance and benefit depend on the specific products.
Some fermentable prebiotics can increase:
- gas,
- bloating,
- or abdominal discomfort,
especially when introduced quickly or at higher doses.
People with gastrointestinal conditions may need individual advice.
Are Postbiotics Better Because They Are More Stable?
Inactivated microbial preparations may have practical stability advantages because they do not need to remain alive.
However, stability does not automatically mean better clinical effectiveness.
A stable product still needs relevant evidence.
How Should You Read a Product Label?
For Probiotics
Look for:
- full strain identification,
- viable amount,
- storage conditions,
- dose,
- evidence for the intended use.
For Prebiotics
Look for:
- the specific substrate,
- daily amount,
- evidence supporting that dose and use.
For Postbiotics
Look for:
- the microbial source,
- how the preparation is defined,
- dose,
- evidence showing a benefit for that preparation.
Common Marketing Mistakes
“Contains live cultures, therefore probiotic.”
Not necessarily.
“Contains fibre, therefore prebiotic.”
Not necessarily.
“Heat-killed bacteria, therefore postbiotic.”
Not automatically.
“50 billion is better than 10 billion.”
Not necessarily.
“Fermented food equals probiotic.”
No.
Scientific definitions exist precisely because these categories are easy to blur.
Frequently Asked Questions
Are probiotics living bacteria?
Probiotics are live microorganisms, which can include bacteria or certain yeasts, with demonstrated health benefits at adequate amounts.
Are prebiotics food for probiotics?
That phrase is a useful simplification but not fully accurate. Prebiotics are selectively utilised by host microorganisms, which may include resident gut microbes rather than only supplemented probiotics.
Are postbiotics dead probiotics?
Not exactly. A postbiotic does not have to originate from an organism that qualified as a probiotic while alive.
Is yoghurt a probiotic?
Some yoghurts may contain probiotic strains, but yoghurt itself is not automatically probiotic.
Do you need all three?
No. There is no requirement for everyone to consume probiotics, prebiotics and postbiotics.
The Bottom Line
Prebiotics, probiotics and postbiotics are not interchangeable marketing words.
They describe three scientifically different approaches:
live microorganisms, selectively used substrates, and inactivated microbial preparations.
The important question is not which category sounds most advanced.
It is whether the specific strain, substrate or preparation has evidence for the benefit being claimed.
Continue Learning
- How to support gut health every day
- Is akkermansia a probiotic?
- Live vs pasteurised akkermansia what's the difference?
Selected Scientific References
- ISAPP. Probiotics, Prebiotics, Synbiotics, Postbiotics and Fermented Foods Defined. Updated 2026.
- Salminen S, Collado MC, Endo A, et al. The International Scientific Association of Probiotics and Prebiotics consensus statement on the definition and scope of postbiotics. Nature Reviews Gastroenterology & Hepatology. 2021.
Educational Disclaimer
This article is for general education only. Product suitability varies by individual health status and intended use.