Probiotics vs Prebiotics
Probiotics are live beneficial bacteria — added to foods like yogurt and sold as supplements. Prebiotics are fibres and other compounds those bacteria feed on. Both are part of supporting a healthy gut microbiome, and they work best together: probiotics introduce or supplement helpful microbes, prebiotics give them something to eat.
Last reviewed on 2026-04-27.
Quick Comparison
| Aspect | Probiotics | Prebiotics |
|---|---|---|
| What they are | Live beneficial bacteria | Fibres and compounds gut bacteria feed on |
| Common sources | Yogurt, kefir, sauerkraut, kimchi, kombucha, supplements | Onions, garlic, leeks, asparagus, bananas, oats, legumes |
| Survive cooking? | Often killed by heat | Yes — fibres are stable |
| Survive stomach acid? | Strain-dependent; some don't reach the colon | Yes — they pass through to the colon |
| Effect | Adds or supplements gut bacteria | Feeds existing gut bacteria |
| Best when used | Together — probiotic + prebiotic = synbiotic | Together — and from a varied plant-rich diet |
Key Differences
1. Living organisms versus their food
Probiotics are bacteria — and sometimes yeasts — that, when consumed in adequate amounts, may benefit the host. The most studied are species in the genera Lactobacillus, Bifidobacterium, and Saccharomyces.
Prebiotics are non-digestible fibres and similar compounds that feed beneficial bacteria already in your gut. Common prebiotics include inulin, fructo-oligosaccharides (FOS), and galacto-oligosaccharides (GOS).
2. Where you find them
Probiotics: fermented foods like yogurt with live cultures, kefir, sauerkraut, kimchi, miso, kombucha, traditional pickles. Also widely sold as capsules and powders.
Prebiotics: high-fibre plant foods. Onions, garlic, leeks, asparagus, artichokes, bananas (especially slightly underripe), oats, barley, legumes, chicory root. The Mediterranean diet is rich in them.
3. Stability
Probiotics are living organisms. Heat, time, and stomach acid can kill them. That's why supplements often use enteric coatings to survive transit, and why fermented foods that are pasteurised may have inactive cultures.
Prebiotics are stable fibres. Cooking, freezing, and stomach acid don't destroy them. They reach the colon intact, which is exactly where you want them.
4. How they work
Probiotics may add or supplement specific bacterial populations, produce beneficial compounds, support the gut barrier, and modulate the immune system. Specific effects are strain-dependent — saying "probiotics help" in general is too broad.
Prebiotics are fermented by colonic bacteria, producing short-chain fatty acids (especially butyrate) that nourish colon cells, lower colon pH, and create a less hospitable environment for some pathogens.
5. Evidence for specific benefits
Probiotic evidence is strongest for: preventing antibiotic-associated diarrhoea, treating acute infectious diarrhoea, and supporting some IBS subtypes. Many other claims are less well-supported.
Prebiotic evidence is strongest for: improving stool regularity, supporting growth of beneficial bacteria, and (for some types) modest improvements in metabolic markers.
6. Together: synbiotics
Probiotics + prebiotics together are sometimes called synbiotics. The probiotic supplies the bacteria; the prebiotic supplies the food.
A diverse diet rich in plants provides both — fermented foods and abundant fibre. That's usually a better long-term approach than supplements.
When to Choose Each
Choose Probiotics if:
- After a course of antibiotics that disrupted your gut.
- For specific conditions where evidence supports a specific strain (talk to a clinician).
- As part of a varied diet rich in fermented foods.
- When you tolerate fermented foods and like them — they fit naturally into many cuisines.
Choose Prebiotics if:
- As the everyday foundation of gut health — they feed the bacteria already there.
- For improving stool regularity and bowel habit.
- As part of any high-fibre, plant-rich eating pattern.
- In situations where you don't tolerate fermented foods, but can eat plenty of plant fibres.
Worked example
Someone recovering from a course of antibiotics drinks kefir daily for a couple of weeks (probiotic) while also eating oats, onions, garlic, and beans (prebiotic) as part of regular meals. The combination supports the recovery of a varied gut microbiome better than either alone. Long term, the dietary fibre habit matters more than the supplement; the gut bacteria need food every day.
Common Mistakes
- "All probiotics are equivalent." Different strains have different effects. The label matters; "contains probiotics" without strain detail is hard to evaluate.
- "Probiotics colonise your gut permanently." Most don't. They pass through, sometimes producing benefits during transit. Daily intake is often needed for sustained effect.
- "Prebiotics are just fibre." All prebiotics are fibres or fibre-like, but not all fibres are prebiotics. The distinguishing feature is being selectively fermented by beneficial gut bacteria.
- "Yogurt always contains live probiotics." Pasteurised yogurts and most fruit yogurts may have inactive cultures. Look for "live and active cultures" on the label.
This is general educational information, not personalised advice. See the disclaimer for the full note.