You are standing at a shelf in a pharmacy or a chemist’s. Three packages next to each other say: probiotic, prebiotic, synbiotic. A fourth one says postbiotic. Only a few years ago, you could hardly find this term in shops. The names differ by just a few letters, so it is easy to think they mean the same thing. However, they describe four separate categories.
Why these names are so easy to confuse
All four terms share the part “-biotic”, which comes from a Greek word that means life. Only the prefixes are different: pro-, pre-, syn- and post-. In everyday speech, this difference gets lost. This is especially true because all four terms are about microorganisms that live in the digestive tract.
The second reason is the speed at which the definitions appeared. Probiotic and prebiotic have been used in scientific literature for decades. Synbiotic got a consensus statement in 2020, and postbiotic only in 2021. For years, people described the same products with different names, and this can still be seen in marketing materials.
The definitions in this article come from ISAPP, the International Scientific Association for Probiotics and Prebiotics. It is an international scientific association that publishes consensus statements. Most of the literature in this area refers to these statements.
Probiotic – live microorganisms
According to the ISAPP consensus from 2014, probiotics are live microorganisms that give a health benefit to the host when given in adequate amounts. The key word is “live”. If the cells in a product have died, the product no longer meets this definition, whatever the package says.
In practice, this means clear requirements. The manufacturer states the number of live cells in CFU (colony-forming units). The manufacturer must keep this number until the end of the shelf life. The number of live cells falls over time, and how fast it falls depends on temperature and humidity. That is why some products must be kept in the fridge.
A reliable description of a probiotic gives the full strain designation: the genus, the species and the code from a culture collection, for example with the prefix DSM or ATCC. The genus name alone is not enough. Observations about one strain do not automatically apply to another strain of the same species.
Read more: Fermented food in Polish cooking – pickles, sour starters, kefir
Prebiotic – food for microorganisms
A prebiotic is not a bacterium. It is a food substance. According to the ISAPP consensus from 2017, it is a substrate that the host’s microorganisms use selectively and that gives a health benefit to the host. A substrate is a material that microorganisms process during their metabolism, which means the chemical changes that take place in the cell.
The most common examples are inulin, fructooligosaccharides (FOS) and galactooligosaccharides (GOS). These are carbohydrates that are not digested in the upper part of the digestive tract. They reach the large intestine unchanged. They are found naturally in chicory, Jerusalem artichoke, onion, garlic and leeks.
It is worth saying that not all dietary fibre is a prebiotic. The definition requires that microorganisms use the substance selectively. Resistance to digestion alone is not enough.
Read more: Dietary fibre – how much we really eat and how much institutions recommend
Synbiotic – a combination of the first two
A synbiotic is a preparation that contains both live microorganisms and a substrate that the host’s microorganisms use. The ISAPP statement from 2020 made an important difference between two types.
A complementary synbiotic is simply a probiotic and a prebiotic together. Each of them meets its own definition separately. A synergistic synbiotic is a combination in which the substrate was chosen especially for the strain in the product. In this second case, the ingredients do not have to meet the definitions of a probiotic and a prebiotic on their own. However, studies must confirm the effect of the combination as a whole.
A synbiotic contains live cells, so it has the same practical limits as a probiotic: a declaration in CFU and the need to keep the cells alive until the end of the shelf life.
Postbiotic – what their work produces
Postbiotic is the newest of the four terms. According to the ISAPP statement from 2021, it is a preparation of inanimate microorganisms or their components that gives a health benefit to the host. Inanimate means that it has no cells that can multiply.
Such a preparation can contain whole inactivated cells, parts of cells and metabolites. Metabolites are compounds that bacteria produce while they grow. The preparation is made by fermentation in controlled conditions. After that, the cells are inactivated, for example with heat.
Read more: What bacterial metabolites are and where they come from in fermentation
Here, the absence of live bacteria is part of the definition, not a production fault. It has technical results: the content is given in units of mass, for example milligrams per portion, not in CFU. Usually, there is also no need for cold storage. One example of a preparation without live bacteria is THESYBIN food supplement. It contains OLINATI.MED® — a fermented strain of Limosilactobacillus reuteri DSM 15693, with added zinc and vitamin B5. After opening, keep in the fridge and use within 30 days.
Read more: Postbiotics – what they are and how they differ from probiotics and prebiotics
Four terms in one table
| Term | What it is | Example | Does it contain live bacteria? |
|---|---|---|---|
| Probiotic | Live microorganisms given in adequate amounts (ISAPP consensus, 2014) | A preparation with live strains from the genus Lactobacillus or Bifidobacterium, with a declaration in CFU | Yes, the bacteria must be alive |
| Prebiotic | A substrate that the host’s microorganisms use selectively (ISAPP consensus, 2017) | Inulin, fructooligosaccharides (FOS), galactooligosaccharides (GOS) | No, it is a food component |
| Synbiotic | A combination of live microorganisms and a substrate for the host’s microorganisms (ISAPP consensus, 2020) | A preparation with a live strain and added inulin or GOS | Yes, live cells are part of it |
| Postbiotic | A preparation of inanimate microorganisms or their components (ISAPP consensus, 2021) | Inactivated cells, their parts or a ferment with metabolites, with a declaration in mg | No, the absence of live cells is part of the definition |
A simple comparison to help you remember
Imagine a garden. A probiotic is the young plants: living organisms. They need the right conditions during transport and storage so that they arrive in good condition.
A prebiotic is the fertiliser. It does not plant anything itself, but it gives food to the plants that already grow in the garden.
A synbiotic is a garden kit in one package: young plants plus a fertiliser chosen for them. You buy both parts together instead of separately.
A postbiotic is the harvest. It is not the young plant and not the fertiliser. It is what the plants produced: collected, processed and ready to use. Like every comparison, this one is simplified. When you judge a specific product, the label matters, not the comparison.
Summary
The four terms describe four different things: live microorganisms, food for them, a combination of the two, and an inanimate preparation made by growing microorganisms. They are not versions of one category or new generations of the same product.
The simplest practical way to tell them apart is to ask about live cells and about the unit of the declared amount. CFU points to a probiotic or a synbiotic. Milligrams per portion point to an inanimate preparation. Ingredients listed as a carbohydrate point to a prebiotic. The full strain designation and the storage conditions are also on the label.
FAQ
Is a postbiotic better than a probiotic?
This is not the right question, because the two categories describe different kinds of preparations, not new versions of the same thing. There are few direct comparisons in the literature between live and inanimate preparations from the same source. The differences we can be sure about are technical: how the product is standardised, the unit of the declared amount and the storage requirements.
Is a prebiotic the same as fibre?
No. Every prebiotic described according to the ISAPP definition belongs to the components that resist digestion. However, not all dietary fibre meets the condition that the host’s microorganisms use it selectively. Cellulose is an example of fibre that people do not usually count as a prebiotic.
Is yoghurt a probiotic, a synbiotic or a postbiotic?
It depends on the specific product and on what the package says. Yoghurt contains live bacterial cultures that are used in fermentation. However, to call it a probiotic in the sense of the ISAPP definition, you would need to name the specific strain and its amount. Fermented products and probiotic preparations are not the same thing.
Sources
- Hill C., Guarner F., Reid G. et al., Expert consensus document. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic, Nature Reviews Gastroenterology & Hepatology, 2014, vol. 11, no. 8, pp. 506-514.
- Gibson G.R., Hutkins R., Sanders M.E. et al., Expert consensus document: The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of prebiotics, Nature Reviews Gastroenterology & Hepatology, 2017, vol. 14, no. 8, pp. 491-502.
- Swanson K.S., Gibson G.R., Hutkins R. et al., The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of synbiotics, Nature Reviews Gastroenterology & Hepatology, 2020, vol. 17, no. 11, pp. 687-701.
- Salminen S., Collado M.C., Endo A. et al., The International Scientific Association of Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of postbiotics, Nature Reviews Gastroenterology & Hepatology, 2021, vol. 18, no. 9, pp. 649-667.
- Commission Regulation (EU) No 432/2012 of 16 May 2012 establishing a list of permitted health claims made on foods, other than those referring to the reduction of disease risk and to children’s development and health.