Probiotics vs prebiotics vs postbiotics: what's the difference?
Last updated: August 2026 · Reviewed by the FactoWiki Editorial Team for clarity and source accuracy
Probiotics are live beneficial microbes. Prebiotics are fibres that feed the microbes already living in you. Postbiotics are the beneficial compounds those microbes produce, or inactivated microbes and their fragments — supplied directly, so nothing needs to survive the journey.
Key takeaways
- Probiotics = live organisms. Prebiotics = their food. Postbiotics = their output.
- Postbiotics are shelf-stable and safe for immunocompromised people, unlike live probiotics.
- Prebiotics feed your existing microbiome, which is why they often cause gas at first.
Probiotics: live and strain-specific
Probiotics are live microorganisms that confer a benefit when taken in adequate amounts. The critical point most marketing obscures is that effects are strain-specific, not species-specific. Lactobacillus rhamnosus GG has evidence for particular uses that other L. rhamnosus strains do not share. A label saying only 'Lactobacillus rhamnosus' with no strain code has no research attached to it. They are transient — they generally do not colonise permanently.
Prebiotics: feeding what is already there
Prebiotics are non-digestible fibres — inulin, FOS, GOS, resistant starch, partially hydrolysed guar gum — fermented by gut bacteria into short-chain fatty acids including butyrate. Because they feed an existing population rather than adding one, they can produce more durable change than a transient probiotic. The trade-off is gas and bloating in the first weeks, which is why starting low and building up matters. People with IBS often tolerate inulin and FOS poorly, as both are FODMAPs.
Postbiotics: the newest category
Postbiotics are the useful outputs — short-chain fatty acids like butyrate, bacterial cell wall fragments, or heat-killed bacteria. Because nothing is alive, they are shelf-stable, unaffected by stomach acid and safe in immunocompromised people, who should avoid live probiotics. The most striking example is pasteurised Akkermansia muciniphila, which outperformed the live form in human trials.
Key ingredients to understand
The ingredients most relevant to this question, with what the evidence actually supports:
- Probiotics (Lactobacillus & friends) — Probiotics are live microorganisms that can support digestion — but their effects are strain-specific, so the exact strains and dose matter more…
- Inulin (Prebiotic Fibre) — Inulin is a prebiotic soluble fibre (from chicory root) that feeds beneficial gut bacteria, supports regularity and calcium absorption, and adds…
- Sodium Butyrate — Butyrate is the short-chain fatty acid your colon cells use as their primary fuel, normally produced by fibre-fermenting bacteria. Supplementing…
- Akkermansia muciniphila — Akkermansia is a mucin-degrading gut bacterium strongly and consistently associated with metabolic health. Unusually for a next-generation…
Frequently asked questions
Should I take all three?
Synbiotics combine probiotics and prebiotics and are a reasonable approach. Adding one at a time tells you what actually helps.
Do I need a high CFU count?
Not necessarily. Match the count to the studied dose for the strain — some work at 1–2 billion. Large CFU numbers are largely a marketing device.
What about fermented foods?
Yoghurt, kefir, kimchi and sauerkraut supply live cultures alongside other nutrients, and a trial found increasing fermented foods raised microbiome diversity and reduced inflammatory markers.
Related on FactoWiki
- Gut & Digestive Health supplements — the full category
- All health answers
- Ingredient evidence guides
- Probiotics (Lactobacillus & friends) — ingredient guide
- Inulin (Prebiotic Fibre) — ingredient guide
- How we review
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