Probiotics vs prebiotics: what's the difference?
Last updated: June 2026 · Reviewed by the FactoWiki Editorial Team for clarity and source accuracy
Probiotics are live beneficial bacteria you add to your gut; prebiotics are the fibres that feed the good bacteria already there. They’re complementary, and products combining both are called synbiotics.
Key takeaways
- Probiotics = live beneficial bacteria (the “seeds”).
- Prebiotics = fibres that feed beneficial bacteria (the “fertiliser”).
- Both can help; prebiotic fibres commonly cause gas at first.
Probiotics: adding good bacteria
Probiotics are live microorganisms — specific strains of beneficial bacteria (and some yeasts) — that you consume in supplements or fermented foods like yoghurt, kefir and sauerkraut. The idea is to add helpful bacteria to your gut, where they may support digestion, the gut lining and the microbiome’s balance. Their effects are strain-specific, and many don’t permanently colonise, so probiotics often work best with ongoing use. Think of them as introducing helpful “seeds.”Prebiotics: feeding good bacteria
Prebiotics are a different thing entirely: they’re types of fibre (such as inulin, FOS and others, found in onions, garlic, bananas, oats and chicory) that humans can’t digest but that beneficial gut bacteria ferment as food. By feeding the good bacteria you already have, prebiotics help them flourish and produce beneficial compounds. If probiotics are the seeds, prebiotics are the fertiliser — they nourish the existing garden rather than planting new ones.Using them together
The two are complementary, and products combining them are called “synbiotics.” For many people, a fibre-rich, varied diet supplies plenty of prebiotics naturally and is the foundation of gut health, while a targeted probiotic may help specific issues. A practical caution: prebiotic fibres are fermentable, so they commonly cause gas and bloating when you ramp up too quickly — and people with IBS may need to go gently. Build up slowly, and let your diet do most of the work.Key ingredients to understand
If you’re weighing up a gut & digestive product, these are two of the ingredients worth knowing about — what they may do, and where the evidence stands:
- 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 than the word 'probiotic'…
- Inulin (Prebiotic Fibre) — Inulin is a prebiotic soluble fibre (from chicory root) that feeds beneficial gut bacteria, supports regularity and calcium absorption, and adds fullness. It's well-supported …
What to check before you buy
Gut formulas depend on strain quality (for probiotics), fibre type and consistency. Check CFU counts and strains, introduce fibre gradually to limit gas, and remember persistent pain, bleeding or major bowel changes need medical assessment, not just a supplement.
Frequently asked questions
What’s the simplest way to remember the difference?
Probiotics are good bacteria (seeds); prebiotics are fibres that feed them (fertiliser).
What’s a synbiotic?
A product combining both probiotics and prebiotics, aiming to add good bacteria and feed them together.
Why do prebiotics cause gas?
They’re fermentable fibres that gut bacteria break down, producing gas — usually easing if you build up slowly.
Related on FactoWiki
- Gut & Digestive supplements — the full category
- Probiotics (Lactobacillus & friends) — ingredient guide
- Inulin (Prebiotic Fibre) — ingredient guide
- PrimeBiome review
- Finessa review
- Compare: finessa vs primebiome
This article is general information, not medical advice. FactoWiki may earn a commission from links on product review pages (never on comparisons). Always check with a qualified healthcare professional about your own situation.