Prebiotics, Probiotics and Postbiotics: What the Three Words Actually Mean (2026 Australian Guide)

Three similar words, three completely different things. What prebiotics, probiotics and postbiotics are, how to read a CFU count, why the strain code after the name matters more than the genus, and which ones actually need the fridge.

By Health & Heal

October 22, 2026 4 min read

Three words that look related and are not interchangeable

Walk down a supplement aisle in 2026 and you will see all three on labels, often on the same shelf, sometimes on the same bottle. The words differ by two letters and describe entirely different categories of product.

Here is the distinction, plainly.

The one-line version

Probiotics are live micro-organisms
Prebiotics are fibres that those micro-organisms feed on
Postbiotics are the by-products left behind, or deliberately inactivated organisms

Probiotics are alive. Prebiotics are food. Postbiotics are not alive. That single fact drives everything else about how they are made, measured and stored.

Probiotics: reading the label properly

The strain code matters more than the name

A proper probiotic label gives you three levels of identification:

Lactobacillus (genus) rhamnosus (species) GG (strain).

The strain code at the end is the specific, catalogued organism that was used in research. Two products can both say Lactobacillus rhamnosus and contain different strains with different documented behaviour.

What to look for: a label that names genus, species and strain. A label that says only "Lactobacillus blend" is telling you less than it could. We go through this in more detail in our guide to reading a probiotic label.

You may also see the newer naming — several Lactobacillus species were reclassified in 2020 into genera such as Lacticaseibacillus and Lactiplantibacillus. A label using the new name is current, not different.

CFU: what the number counts

CFU stands for colony-forming units — a count of viable organisms. You will see anything from 1 billion to 100 billion.

The important question is when the count was taken:

CFU at time of manufacture — the number when it left the factory. It will be lower by the time you open it
CFU at expiry — a guarantee of what remains at the end of shelf life. This is the more meaningful figure

A product guaranteeing 10 billion at expiry may well deliver more to you than one advertising 50 billion at manufacture. Check which basis a label uses before comparing two numbers.

Single strain or multi-strain

Neither is automatically better. A single well-documented strain at a researched dose is a different proposition from a twelve-strain blend where no individual strain is listed at a meaningful count. If a multi-strain product gives one total CFU across twelve organisms, you cannot tell how much of each you are getting — the same problem we describe in why some supplements have 20 ingredients.

Prebiotics: fibre by another name

Prebiotics are not alive and do not need refrigeration. They are specific fibres and carbohydrates that resist digestion in the upper gut.

The ones you will see on labels:

Inulin — commonly from chicory root
FOS (fructo-oligosaccharides)
GOS (galacto-oligosaccharides)
Resistant starch — often from green banana or potato
Partially hydrolysed guar gum (PHGG)
Acacia fibre

Dose is measured in grams, not milligrams. This is the most common place marketing and reality diverge. Research on prebiotic fibres typically uses several grams per day. A capsule containing 200mg of inulin contains a twentieth of a gram. If a product lists its prebiotic in milligrams, read the number carefully.

Prebiotic fibres are also a common cause of wind and bloating when introduced quickly, which is why most labels suggest starting low.

Synbiotics

A "synbiotic" is simply a product containing both a probiotic and a prebiotic. Useful shorthand, not a separate category of ingredient.

Postbiotics: the newest word

Postbiotics are the one most people have not encountered. The 2021 ISAPP consensus definition describes them as preparations of inanimate micro-organisms, or their components.

In practice that covers:

Heat-treated or inactivated organisms — sometimes labelled "paraprobiotic" or "HK" (heat-killed), for example HK Lactobacillus plantarum
Short-chain fatty acids such as butyrate
Cell wall fragments and metabolites

The practical consequence of being inanimate: no CFU count, no refrigeration, no viability to lose. A postbiotic has a straightforward shelf life in the way a vitamin does.

This is a younger field than the other two. The research base is smaller.

Storage: which ones care

Probiotics	Depends on the strain. Some are shelf-stable, some require refrigeration. Follow the label — guessing costs you the product
Prebiotics	Cool, dry cupboard. Powders clump in humidity
Postbiotics	Cool, dry cupboard. Nothing alive to kill

For probiotics specifically, heat is the enemy. A bottle left in a car in an Australian summer may contain a fraction of its stated count, and nothing on the outside of the bottle will tell you. Our guide to storing supplements in an Australian summer covers where to keep them and what spoils first.

Four things worth checking before you buy

1. Is the strain named? Genus, species and strain code, not just a genus.

2. Is CFU guaranteed at expiry or at manufacture? They are not the same claim.

3. Is the prebiotic dose in grams or milligrams? Grams are the unit used in the research.

4. Does it need the fridge? If the label says so and you store it in a cupboard, you have bought something that no longer matches its label.

The short version

Probiotics are alive and need a strain code and a CFU-at-expiry figure. Prebiotics are fibre and need to be dosed in grams. Postbiotics are inactivated and need neither a CFU count nor a fridge.

Different categories, different labels, different storage. Worth knowing which one is in your hand.