Four Terms, Clearly Defined
These 'biotic' words get mixed up constantly. Here's how the NIH Office of Dietary Supplements defines them:
- Probiotics are live microorganisms intended to confer a health benefit when consumed.
- Prebiotics are 'typically complex carbohydrates (such as inulin and other fructo-oligosaccharides) that microorganisms in the gastrointestinal tract use as metabolic fuel' [1]. In other words, prebiotics are non-living fibers that feed beneficial bacteria already living in your gut.
- Synbiotics are 'commercial products containing both prebiotics and probiotic microorganisms' [1] — the two combined in one product.
- Postbiotics are 'preparations comprised of dead, intact, or fragmented microorganisms, with or without their metabolites, that confer a health benefit on the host' [1] — a newer category that, notably, contains no live organisms.
The Simple Mental Model
| Term | Living? | What it is |
|---|---|---|
| Probiotic | Yes | Live beneficial microbes |
| Prebiotic | No | Fiber that feeds your gut microbes |
| Synbiotic | Yes (+ fiber) | Probiotic + prebiotic together |
| Postbiotic | No | Non-living microbial preparations (± their byproducts) |
Where the Evidence Stands
For all of these, benefits are specific to the particular strain, fiber, or preparation studied — results don't automatically transfer between products. The NCCIH notes that probiotic effects can be strain-specific and that for many uses, the right dose and who benefits most aren't yet established [2]. Postbiotics are the newest term, with the least consumer research so far.
For more on reading probiotic labels, see CFU Explained and the Probiotics Complete Guide.
Practical Takeaways
- 'Probiotic' = alive; 'prebiotic' = food for microbes; 'postbiotic' = non-living preparation.
- A 'synbiotic' is just both combined.
- Match the specific product to what's actually been studied for your goal, and treat broad category claims cautiously.