Postbiotic

What is a postbiotic?

For years, products derived from non-living microbes went by several labels: paraprobiotics, heat-killed probiotics, bacterial lysates, metabolites. In 2021 an ISAPP panel (Salminen et al., Nat Rev Gastroenterol Hepatol) proposed a shared definition: a preparation of inanimate microorganisms and/or their components that confers a health benefit on the host.

The panel deliberately chose “inanimate” over “dead” or “inert”, because those words imply a lack of biological activity, which may not be the case.

What it includes and what it does not

Under the consensus, a postbiotic:

• starts from well-characterised microorganisms that are deliberately inactivated (by heat, pressure or other methods);
• may contain whole cells, cell fragments and, optionally, metabolites;
• must have shown a health benefit in the target host.

Excluded are purified metabolites (for example isolated short-chain fatty acids, proteins or exopolysaccharides), cell-free filtrates and vaccines. Nor does a probiotic that has lost viability in the packet count: the inactivated preparation must be defined and tested as such.

How it works

Proposed mechanisms resemble those of some probiotics without requiring the organism to be alive: cell-wall components interacting with the immune system, effects on the epithelial barrier, or metabolites with local activity. Because they are not viable, postbiotics tend to be more stable and do not need refrigeration, which is useful in foods and in settings where cold storage is difficult.

What the evidence says

The evidence is emerging. There are trials of certain inactivated preparations, for instance fermented infant formulas and specific heat-treated strains, but studies are heterogeneous and results for one preparation cannot be applied to another. Part of the research base comes from cell and animal models. The consensus itself calls for more controlled human trials and for thorough characterisation of each product.

Example

A nutrition researcher designing a trial wants to compare a live strain with its heat-inactivated counterpart. Following the ISAPP criteria, she documents the parent strain, the inactivation method and how she confirmed that no viable cells remain, and she pre-specifies the clinical outcome. Only if the inactivated preparation shows a benefit in that trial could it be described as a postbiotic for that use.

Postbiotics in clinical practice

Xenogene neither makes nor recommends postbiotics. What it can provide is context about the gut ecosystem: a gut microbiota analysis describes its composition, and metabolomics measures faecal metabolites such as butyrate. These results do not indicate which postbiotic to use; that decision rests with the healthcare professional, as outlined on the professionals page.