For years, the word “postbiotic” meant different things in different publications. Some authors used it for inactivated bacterial cells. Others used it for the liquid left after growing bacteria. Others still used it for a single compound taken from fermentation. So two papers with the same word did not always describe the same thing. In 2021, ISAPP published a consensus statement to solve this problem.
What ISAPP is
ISAPP stands for the International Scientific Association for Probiotics and Prebiotics. It is an international scientific association that works on probiotics and related terms. Its members are researchers from universities and research centres, for example in microbiology, gastroenterology and food technology.
The association is not a regulator and does not make legally binding decisions. It publishes consensus statements. Expert panels prepare these documents, and other scientists review them. The statements have become a point of reference for the literature in this area.
By 2021, ISAPP had published statements on probiotics (2014), prebiotics (2017) and synbiotics (2020). Postbiotic was the last term in this group without an agreed definition.
Read more: Probiotic, prebiotic, synbiotic, postbiotic – four terms that people often confuse
How confusing the terms were before 2021
People used at least a dozen names for preparations without live cells: parabiotic, metabiotic, ghostbiotic, biogenic, “inactivated probiotic”, “tyndallised bacteria”, “bacterial lysate” and “postbiotic”. None of these terms had a definition that the scientific community accepted.
This was a practical problem, not only a language problem. An author of a literature review could not be sure that the papers they compared were about the same kind of preparation. A manufacturer who described a product had no point of reference.
The research itself also started to look at things differently. Some observations from work on probiotics also appeared with preparations without live cells. This made researchers look at the structure of the cell and at the compounds it produces. As the number of such publications grew, it became clear that the terms needed order.
Read more: Postbiotics in scientific research – what we already know and what we do not know yet
What the official definition says
According to the ISAPP statement from 2021, a postbiotic 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.
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 must follow the list of claims permitted by Regulation (EU) No 432/2012.
Three key parts of the definition
The expert panel set conditions that must all be met together. We can put them into three groups.
- An identified starting material. The source microorganism must be described at the level of the strain. The preparation must contain inanimate cells or their components, with or without metabolites.
- A described and repeatable process. The inactivation method must be documented. Inactivation means that the cells lose the ability to multiply. The growth medium and the production conditions must also be documented.
- Confirmed safety and effect in the target group. The preparation must be safe for its stated use. The benefit must be shown for this specific preparation and this group.
People sometimes leave out the last condition. Data for one strain and one inactivation method do not automatically apply to another preparation, even if both have the same name.
What the definition excludes on purpose
The authors of the statement also said what the term should not cover. These exclusions set the limits of the category.
| What people sometimes call a postbiotic | Why it does not fit the ISAPP definition |
|---|---|
| A single purified compound from a culture | It is a chemical substance with a known structure, not a microbiological preparation |
| Vaccines | A separate category that works in a different way and has different legal requirements |
| A preparation with live cells | It contains microorganisms that can multiply, so it matches the definition of a probiotic |
| A preparation without strain identification | It does not meet the condition that the starting material must be described |
One point of disagreement is the cell-free fraction, which means only the liquid left after growing the bacteria, with its metabolites. According to the consensus, the preparation should contain inanimate cells or their components. So a material made only of metabolites does not fit the definition.
Why a shared definition matters in practice
For scientists
A shared definition makes it possible to compare publications about similar preparations. It also sets the minimum information a paper should give: the strain designation, the inactivation method and a description of what the preparation contains. Without this, systematic reviews and meta-analyses are based on mixed material. These are studies that collect the results of many other studies.
It also helps with planning studies, because it shows what to document so that other teams can compare the results with their own work.
For consumers
An agreed term leads to a clearer label. If a product is described as a postbiotic, you can check the label for three things: the full strain designation, information that there are no live bacterial cultures, and the content in units of mass per portion.
However, it does not guarantee that every product that uses this word meets the conditions. Nobody checks a trade name in the same way as a scientific category. What the label says is still the thing to check.
Read more: Postbiotics – what they are and how they differ from probiotics and prebiotics
Is the definition widely accepted?
Not fully. Soon after the statement came out, the same journal published a critical letter. The authors of the consensus answered it in a separate text.
The main criticism is about the requirement for cells or their components. The critics say that it excludes preparations made only of metabolites, which many papers study as the same kind of material. So some teams use a wider interpretation that also includes cell-free fractions.
This discussion is not settled. So when you read a scientific paper or a product description, check which definition the author uses. Do not assume that everyone uses the word in exactly the same way.
Summary
A separate term was necessary because a dozen competing names made it impossible to compare studies and to describe products reliably. The ISAPP statement from 2021 gave one definition, together with conditions that a preparation must meet.
The definition covers inanimate microorganisms or their components. It requires strain identification, a documented process and data for the specific preparation. Not everyone agrees with it, and it is still under discussion. Keep this in mind when you read publications and labels.
FAQ
Is the ISAPP definition legally binding?
No. ISAPP is a scientific association, not a regulator, so its statements bring order to the work of researchers. The rules on labelling food and food supplements in the European Union come from separate legal acts.
Does every product called a postbiotic meet this definition?
There is no such guarantee, because nobody checks the word on a package against scientific criteria. The label is still the practical test: the full strain designation, information that there are no live bacterial cultures, and how the content is given.
Why was the definition only created in 2021?
The number of publications about preparations without live cells grew slowly. For a long time, it was too small to make an agreement on the terms necessary. ISAPP wrote its statements in the order in which each research area became mature, and postbiotics were the newest area.
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.
- Aguilar-Toalá J.E., Arioli S., Behare P. et al., Postbiotics – when simplification fails to clarify, Nature Reviews Gastroenterology & Hepatology, 2021, vol. 18, no. 11, pp. 825-826.
- Salminen S., Collado M.C., Endo A. et al., Reply to: Postbiotics – when simplification fails to clarify, Nature Reviews Gastroenterology & Hepatology, 2021, vol. 18, no. 11, pp. 827-828.