What is the difference between probiotics and postbiotics?

Probiotics are live bacteria, such as Lactobacillus and Bifidobacterium species, which you need to take in sufficient quantities to have an effect. They can influence the composition of gut bacteria and help suppress disease-causing bacteria. The key word is 'live': without live bacteria, they are not probiotics.

Postbiotics are derived from those same micro-organisms, but are no longer alive themselves. Think of bacteria that have been heated and thereby killed, or of substances that bacteria produce during their lifetime, such as short-chain fatty acids. Postbiotics are stable, easier to store and transport than live probiotics, and are considered safer for people with a weakened immune system. In those individuals, live bacteria can in rare cases pose risks.

But do postbiotics work just as well as probiotics? A randomised, double-blind, placebo-controlled study of 200 people with irritable bowel syndrome (diarrhoea type) compared a live Bifidobacterium longum strain with the heated, non-live variant of that same strain. After twelve weeks, the symptom score fell by an average of 173 points in the live probiotic group and by 177 points in the postbiotic group, compared with 60 points in the placebo group. Both were comparably effective. This is promising, but it concerns a single study involving one specific strain and one condition.

Beyond this comparison, the evidence for most applications of both probiotics and postbiotics remains limited. For intestinal conditions such as IBD, for obesity, and for sleep problems, results so far have been mixed or insufficient. The only microbiome intervention with a truly proven benefit is faecal transplantation for recurrent Clostridioides difficile infection. For all other conditions, it is still too early for firm recommendations.