The word “postbiotic” appears more and more often in descriptions of food supplements, in industry articles and in materials from manufacturers. The problem is that people often use it in place of probiotic, prebiotic or synbiotic. Each of these terms means something different. People also sometimes describe a postbiotic simply as “dead bacteria”, which is a simplification. Below, we explain the terms. We base this on the definition that ISAPP, an international scientific association, published in 2021.
Where the term postbiotic comes from
The terms “probiotic” and “prebiotic” have been used in scientific literature for decades. Both have formal consensus definitions. Postbiotic is a much newer term. It comes from something researchers noticed while they studied probiotics: some effects described in experiments also appeared when the products had no living bacterial cells.
Live bacteria were not always necessary to see changes. So researchers started to pay more attention to the structures of the cell itself and to the compounds it produces when it grows. Together, these compounds are called metabolites. Metabolites are the products of chemical changes that take place in the cell.
Read more: What bacterial metabolites are and where they come from in fermentation
For years, people used many names for such products: parabiotic, metabiotic, ghostbiotic, “tyndallised bacteria”, “inactivated probiotics”. None of these names had one agreed definition. This made it hard to compare publications. It also confused consumers.
In 2021, the International Scientific Association for Probiotics and Prebiotics (ISAPP) published a consensus statement that put these terms in order. ISAPP is an international scientific association that works on probiotics and prebiotics. Today, this document is the most common point of reference in discussions about postbiotics.
The definition of a postbiotic – what exactly the term includes
According to the ISAPP statement, a postbiotic is a preparation of inanimate microorganisms or their components that gives a health benefit to the host. It is important to say this clearly: this is a scientific definition that describes a research category. It is not a basis for health claims about specific products. In the European Union, communication about food supplements may only use health claims permitted by Regulation (EU) No 432/2012.
The definition has several conditions. All of them must be met together:
- the source microorganism must be identified and described at the level of the strain, not only the species,
- the preparation must be inanimate, which means it has no cells that can multiply,
- it can contain whole inactivated cells, parts of cells or the metabolites that come with them,
- the production process must be described and repeatable,
- the preparation must be safe for its stated use and tested in the target group.
Marketing materials sometimes leave out the last condition. To call something a postbiotic in the ISAPP sense, you need data about that specific preparation, not general data about the category. Results for one strain and one inactivation method do not automatically apply to another.
What is a postbiotic and what is not
A probiotic is not a postbiotic, because by definition it contains live microorganisms. A prebiotic is not a postbiotic either. A prebiotic is a food substrate, not a material that comes from microorganisms.
Read more: Probiotic, prebiotic, synbiotic, postbiotic – four terms that people often confuse
ISAPP also excluded purified single compounds taken from a bacterial culture, and vaccines. In this system, a single fatty acid or an isolated protein is a chemical substance, not a postbiotic.
The ISAPP definition is discussed in scientific literature. Some researchers think that the requirement for cells or cell components is too strict. They suggest that the term should also cover preparations that contain only the metabolic fraction. This discussion is not settled. That is why product descriptions use the word in different ways, and not always in line with the consensus.
Probiotic, prebiotic, postbiotic – three terms in one table
| Criterion | Probiotic | Prebiotic | Postbiotic |
|---|---|---|---|
| Short definition | Live microorganisms that give a health benefit to the host when given in adequate amounts (ISAPP consensus, 2014) | A substrate that the host’s microorganisms use selectively and that gives a health benefit to the host (ISAPP consensus, 2017) | A preparation of inanimate microorganisms or their components that gives a health benefit to the host (ISAPP consensus, 2021) |
| Example | A preparation with live strains from the genus Lactobacillus or Bifidobacterium, with a stated number of colony-forming units (CFU) | Inulin, fructooligosaccharides (FOS), galactooligosaccharides (GOS) | A preparation of inactivated bacterial cells or their parts, or a ferment that contains metabolites |
| Does it contain live bacteria? | Yes, the bacteria must be alive | No, it is a food component, not a microorganism | No, the absence of live cells is part of the definition |
| Storage requirements | Often cold storage or strict control of temperature and humidity; the number of live cells falls over time | Usually room temperature; the ingredients are stable | Usually room temperature; there is no need to keep cells alive; details depend on the form of the product |
There is a fourth term that people also confuse with the others. A synbiotic is a combination of live microorganisms and a substrate that the host’s microorganisms use. ISAPP described it in a separate statement in 2020.
How postbiotics are made
The role of fermentation
The starting point is growing a chosen bacterial strain in controlled conditions, on a defined growth medium. Fermentation is a process without oxygen in which the cells change the substrate. During fermentation, the cells use up the available nutrients and release the products of their metabolism. These include organic acids, such as lactic acid and acetic acid, short-chain fatty acids, peptides and exopolysaccharides. Some strains also produce B vitamins.
The make-up of this mixture is not random, but it is not fixed either. It depends on the strain, the growth medium, the temperature, the pH and how long the process lasts. If any of these conditions changes, the profile of the metabolites also changes. That is why repeatable growing conditions are a basic technical requirement in this category.
Read more: Limosilactobacillus reuteri – the story of a strain that changed its name
What happens to the metabolites after the process ends
After fermentation, the culture is inactivated. This means the cells lose the ability to multiply. Producers use heat treatment for this, including tyndallisation and pasteurisation. They also use high pressure, ultrasound, UV radiation or freeze-drying (lyophilisation). The choice of method matters for the final result. Different techniques damage the structure of the cell and its compounds to different degrees.
The next steps are usually separating the solid fraction, concentrating and standardising. Standardising means bringing each batch to a similar, stated content of a chosen marker. The content is then given in units of mass, for example milligrams per portion. It is not given in CFU, because CFU only refers to live cells.
Read more: A supplement without live bacterial cultures – how it is possible and what it changes
Why having no live bacteria can be a practical feature, not a weakness
Products with live microorganisms need very careful handling along the whole supply chain. The number of live cells falls over time. How fast it falls depends on temperature, humidity and the make-up of the product. The manufacturer must state the number of cells at the end of the shelf life. This usually means adding extra cells at the start.
An inanimate preparation does not have this limit, because there are no live cells to keep alive. This makes it easier to standardise each batch and to transport the product at room temperature. It also makes it easier to combine it with other ingredients, including in liquid forms and at low pH.
This difference is about technology and product design. It does not mean that one category works better than the other. There are few direct comparisons in the literature between live and inanimate preparations from the same source, and their results are not always consistent.
What research on postbiotics says
Scientists study inanimate preparations in several areas. For example, they look at how these preparations interact with cells of the gut lining and of the immune system. They also look at their effect on the make-up of the community of microorganisms that live in the digestive tract.
Read more: Gut microbiota – how it develops and what shapes it throughout life
A large part of the available data comes from in vitro studies, which means studies on cell cultures outside the body, and from animal models. Results from such studies are preliminary. They do not directly apply to the human body. There are fewer studies with people. They often include small groups and use different methods, which makes it hard to compare results (Salminen et al., 2021).
Another area that researchers describe separately is infant formula that is fermented and then inactivated. A systematic review of eleven randomised trials found these products safe and well tolerated. However, it did not reach a clear conclusion that any of these formulas is better than standard formula (Szajewska et al., 2022).
What we do not know yet
There are many open questions in this category, and an honest description should include them:
- there is no standard inactivation method and no standard way to describe what a preparation contains, which makes it hard to compare publications,
- in most cases, we do not know which part of the preparation, the cells or the metabolites, is behind the observations,
- for most available preparations, there are no long-term studies with people,
- there is no widely accepted unit of measurement that works like CFU does for probiotics,
- the list of health claims permitted by Regulation (EU) No 432/2012 has no claims about postbiotics as a category.
How to recognise a postbiotic on a supplement label
The label is the first place where you can check what the product really is.
- Full strain designation. A reliable description gives the genus, the species and the strain designation from a culture collection, for example with the prefix DSM, ATCC, LMG or CNCM. The genus name alone is not enough.
- Words that show the cells are not alive. Terms such as “inanimate”, “inactivated”, “no live bacterial cultures”, “lysate”, “ferment” or “tyndallised” describe a preparation without cells that can multiply.
- Unit of the declared amount. Content given in milligrams per portion fits an inanimate preparation. A declaration in CFU refers to live cells, so in this context it would not fit.
- What the declared amount refers to. Check whether the amount refers to the recommended daily portion or, for example, to 100 g of the product.
- Storage conditions. No need for cold storage fits an inanimate preparation, but on its own it proves nothing.
Warning signs are: no identification of the strain, descriptions that suggest a medical treatment effect, and claims that are not in Regulation (EU) No 432/2012. 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.
Summary
Probiotic, prebiotic and postbiotic are three different categories, not versions of the same idea. A probiotic contains live microorganisms. A prebiotic is a substrate for the host’s microorganisms. A postbiotic is an inanimate preparation made of cells, their components or the metabolites that come with them.
The absence of live bacteria is part of the definition of a postbiotic. It has clear technical results: easier standardisation and simpler storage. However, it is not an argument that one category is better than another.
Knowledge about postbiotics is still at an early stage, and most data comes from in vitro studies and animal models. When you look at a specific preparation, the most practical place to start is still the label: the full strain designation, a clear statement that the cells are not alive, and the declared content per portion.
FAQ
Is a postbiotic just dead bacteria?
That is a simplification. According to the ISAPP definition, a postbiotic is a prepared and described preparation. It can contain whole inactivated cells, parts of cells and metabolites made while the bacteria grew. Bacteria dying in any product does not make that product a postbiotic.
Do you need to keep a postbiotic in the fridge?
Usually not, because there are no live cells to keep alive in an inanimate preparation. However, the requirements depend on the form of the product and what it contains. Always follow the manufacturer’s information on the package.
How is a postbiotic different from a synbiotic?
A synbiotic is a combination of live microorganisms and a substrate that the host’s microorganisms use. ISAPP described it in a statement in 2020. A postbiotic does not contain live cells, so the two categories cannot overlap on this point.
How can you tell that a supplement contains a postbiotic?
The label should give the full strain designation with its collection number and clearly say that there are no live bacterial cultures. The content is then given in units of mass per portion, not in CFU.
Sources
- 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.
- 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.
- Regulation (EC) No 1924/2006 of the European Parliament and of the Council of 20 December 2006 on nutrition and health claims made on foods.
- 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.
- Szajewska H., Kołodziej M., Skórka A., Pieścik-Lech M., Infant Formulas With Postbiotics: An Updated Systematic Review, Journal of Pediatric Gastroenterology and Nutrition, 2022, vol. 74, no. 6, pp. 823-829.