What is the difference between probiotics and postbiotics?
Postbiotics appear to work just as well as live probiotics for irritable bowel syndrome and are safer in people with a weakened immune system, but for most other complaints there is still too little evidence to say that either genuinely helps.
Probiotics are live bacteria, such as Lactobacillus and Bifidobacterium species, that need to be taken in sufficient quantities to have an effect. They work, among other things, by altering the composition of your gut bacteria and inhibiting pathogens, including outside the gut, for example in the oral cavity.
Postbiotics are non-living substances derived from those same bacteria. Think of heat-treated bacteria or the compounds that bacteria secrete, such as certain fatty acids. They are inactive, yet retain a biological effect on the body. A concrete example from research is a heat-treated variant of Bifidobacterium longum.
A practical advantage of postbiotics is safety: because they contain no live bacteria, there is no risk of them causing an infection in people with a weakened immune system. They are also easier to store and transport than live probiotics.
Whether you take live probiotics or the heat-treated postbiotic appears to make little difference in terms of effect. In a randomised study involving 200 participants with irritable bowel syndrome (with diarrhoea as the main complaint), symptom scores after 84 days fell by approximately 174 points with the live bacterium and 178 points with the heat-treated postbiotic. With placebo, the reduction was only around 60 points. This suggests that the bacterium does not necessarily have to be alive in order to work.
That said, this finding should not be generalised too broadly. For most conditions, such as obesity or inflammatory bowel diseases, there is still too little evidence that probiotics or postbiotics genuinely help. Only faecal transplantation has proven benefit at this point, and specifically for recurrent Clostridioides difficile infection. The indications that these agents improve sleep or stress are also contradictory and not yet convincing.
Claims based on multiple studies, including one randomised double-blind study (n=200, PMID 38630015), a definition study (PMID 36968114), a safety perspective (PMID 37513229) and multiple reviews. Evidence is strongest for IBS-D; for other conditions it is predominantly observational or insufficient.