Prebiotics vs Probiotics: What the Difference Is
Probiotics are live micro-organisms dosed in CFU. Prebiotics are non-digestible fibres — inulin, FOS, GOS — dosed in grams, which feed organisms already present. They are not substitutes for one another and cannot be compared on the same units.
Prebiotics and probiotics sit next to each other on shelves and mean different things. One is a live organism; the other is food for organisms already present. They are dosed in different units and are not substitutes for one another.
Probiotics
Live micro-organisms, dosed in CFU — colony forming units, usually stated in billions — and identified by genus, species and strain. Covered in our guides to CFU counts and strains.
Prebiotics
Non-digestible food components, typically fibres, that serve as substrate for micro-organisms in the gut. Dosed in grams. Inulin, fructo-oligosaccharides (FOS) and galacto-oligosaccharides (GOS) are the ones you will most often see named on a label.
Because prebiotics are fibres, they overlap with the fibre category — see our fibre comparison. A product sold as a prebiotic and a product sold as a fibre supplement may contain the same ingredient.
Synbiotics
Products combining both. Reading one means reading two sets of figures: the CFU count and strains for the probiotic part, and the gram dose for the prebiotic part. A synbiotic that states a large CFU number and an unstated or very small prebiotic amount is mostly a probiotic.
Postbiotics
A newer label term describing preparations of inactivated micro-organisms or their components. Because the organisms are not live, CFU is not the relevant measure, and these products state content differently. Treat the term as a signal to read the panel carefully rather than as a familiar category.
Comparing across the three
You cannot compare grams against CFU. When a product carries both, evaluate each part against products of that type — the probiotic part against other probiotics, the fibre part against other fibre supplements.
A note on tolerance
Prebiotic fibres are fermented in the gut, and introducing them quickly is a common cause of bloating and wind. Where a product suggests building up gradually, that instruction is there for a reason.
Our probiotic comparison and fibre comparison filter each category separately.
References
- NIH Office of Dietary Supplements — Probiotics (Health Professional Fact Sheet)
- NCCIH — Probiotics: What You Need To Know