Most people know probiotics are the “good bacteria.” Fewer can explain what prebiotics actually are, or how the two relate to each other. And postbiotics (the compounds your gut bacteria produce when everything is working properly) barely register at all.
Understanding the difference between prebiotics and probiotics changes how you think about gut health. This guide covers what each one does, how they work together, where postbiotics and synbiotics fit in, and whether you need to supplement any of them.
Prebiotics vs Probiotics: The Key Difference
Probiotics are live microorganisms (mostly bacteria, sometimes yeasts) that provide a health benefit when consumed in adequate amounts. That definition comes from the International Scientific Association for Probiotics and Prebiotics (ISAPP), and it still holds (Hill et al., 2014).
Prebiotics are not bacteria. They are non-digestible compounds, mainly fibres and oligosaccharides, that selectively feed beneficial bacteria already in your gut. The ISAPP formalised that definition in a 2017 consensus paper (Gibson et al., 2017), specifying that not all fibre counts as prebiotic. Only substrates that are selectively used by host microorganisms and confer a health benefit qualify.
The simplest way to think about it: probiotics are the workers, prebiotics are the fuel. One without the other is incomplete.
Prebiotics, Probiotics and Postbiotics at a Glance
| Type | What it is | Examples | Food sources |
|---|---|---|---|
| Prebiotics | Non-digestible fibres and compounds that feed beneficial gut bacteria | Inulin, FOS, GOS, pectin, polyphenols | Garlic, onions, oats, leeks, bananas, asparagus, legumes |
| Probiotics | Live microorganisms that confer a health benefit when consumed in adequate amounts | L. rhamnosus GG, S. boulardii, L. plantarum | Live yoghurt, kefir, kimchi, sauerkraut, miso |
| Postbiotics | Bioactive compounds produced by probiotic bacteria during fermentation | SCFAs (butyrate, propionate), bacteriocins, enzymes, peptides | Fermented foods; also produced naturally in the gut |
| Synbiotics | A combination of prebiotics and probiotics designed to work together | L. plantarum + FOS, yoghurt + banana | Functional foods, targeted supplements, some fermented products |
What Are Prebiotics?
Prebiotics are the food that probiotic bacteria eat. More precisely, they are selectively fermented compounds that stimulate the growth and activity of beneficial bacteria in the gut.
They are not bacteria themselves. They are the substrate that allows beneficial bacteria to thrive. The most common dietary prebiotics include inulin and fructooligosaccharides (FOS), found in foods like chicory root, garlic, onions, Jerusalem artichokes, and leeks. Pectin from apples, galactooligosaccharides (GOS) from legumes, and certain polyphenols also have prebiotic properties.
This is where most people’s gut health strategy has a gap. Taking probiotic bacteria without adequate prebiotic substrate is like stocking a kitchen with chefs but no ingredients. The bacteria arrive but don’t have what they need to establish and multiply.
What Are Probiotics?
Probiotics are the live bacteria and yeasts that colonise your gut and contribute to a healthy gut microbiome. You get them from fermented foods like yoghurt, kefir, sauerkraut, and kimchi, or from supplements.
The key word in the definition is live. Probiotic bacteria need to survive the journey through the stomach and small intestine to reach the colon, where they do most of their work. Delivery format and storage conditions matter more than most labels acknowledge.
Not all probiotic strains do the same thing. Lactobacillus rhamnosus GG is one of the most studied for gut barrier function and immune support. Saccharomyces boulardii is a yeast-based probiotic with strong evidence for antibiotic-associated diarrhoea. Lactobacillus plantarum is particularly adaptable and survives well in fermented environments. Strain specificity matters. “Take a probiotic” is too vague to be useful advice.
What Are Postbiotics?
Postbiotics are the bioactive compounds produced by probiotic bacteria when they ferment prebiotic substrates. They include short-chain fatty acids (like butyrate, which fuels the cells lining the gut wall), organic acids, bacteriocins, enzymes, and other metabolic byproducts.
In other words, postbiotics are what you actually get when prebiotics and probiotics work together properly. They are the end product of a functioning gut fermentation process. Increasingly, researchers think postbiotics may account for much of the benefit attributed to probiotics (Salminen et al., 2021).
A 2025 meta-review in PMC found that postbiotics increased levels of Akkermansia (associated with metabolic health) while reducing pro-inflammatory bacterial populations, suggesting they may have direct modulatory effects beyond simply being a byproduct.
For a detailed breakdown of what postbiotics are and what the research shows, see our full guide to postbiotics.
How Prebiotics, Probiotics and Postbiotics Work Together
The relationship is sequential, not parallel.
Prebiotics arrive in the colon intact, because the human gut can’t digest them directly. Probiotic bacteria ferment those prebiotics, using them as fuel to grow, multiply, and out-compete less beneficial microbes. As they ferment, they produce postbiotics: the compounds that directly support gut lining integrity, regulate immune responses, and shape the overall gut environment.
Taking probiotics without prebiotics means the bacteria arrive without a reliable food source. Taking prebiotics without the right beneficial bacteria means the substrate is available, but whether it gets used depends on the existing state of your microbiome.
This is why fermented foods tend to support gut health more effectively than isolated probiotic capsules. A traditionally fermented food contains live bacteria, natural prebiotic compounds from the original substrate, and the postbiotic compounds already produced during fermentation. All three, together, in a single food.
What Are Synbiotics?
A synbiotic is a product that combines prebiotics and probiotics in a single preparation. The ISAPP formalised the definition in a 2020 consensus paper (Swanson et al., 2020), distinguishing between two types:
- Complementary synbiotics, where the prebiotic and probiotic are chosen independently, each with evidence of benefit on their own.
- Synergistic synbiotics, where the prebiotic is specifically selected to support the growth of the co-administered probiotic strain.
The synergistic type is more targeted and, when the pairing is well-matched, tends to produce more consistent results. The Swanson et al. review confirmed that synbiotics produce more reliable benefits than probiotics taken without prebiotic support, particularly when the prebiotic substrate is matched to the specific strains included.
A Caution on Probiotics After Antibiotics
A common recommendation is to take probiotics during or after a course of antibiotics to “restore” gut bacteria. The logic seems sound, but the evidence is more nuanced.
Research from the Weizmann Institute (Suez et al., 2018, published in Cell) found that while standard probiotic supplements did colonise the post-antibiotic gut, they actually delayed the return of the native microbiome by up to five months. The control group (who received no probiotics) recovered their original microbiome composition within three weeks.
This doesn’t mean all post-antibiotic probiotic use is harmful. Saccharomyces boulardii has strong evidence for reducing antibiotic-associated diarrhoea specifically. But the blanket advice to “take a probiotic after antibiotics” oversimplifies a more complex picture.
Prebiotics and fermented foods may be a safer default for general post-antibiotic recovery, allowing the native microbiome to re-establish on its own terms. For more on this, see our guide to restoring gut health after antibiotics.
Do You Need Prebiotics and Probiotics, or Both?
For most people, both. But the priority order matters.
If your diet is already rich in prebiotic foods (plenty of vegetables, legumes, whole grains, and fruits), your existing microbiome is getting what it needs. Adding a well-chosen probiotic on top of that foundation makes sense.
If your diet is low in fibre and in prebiotic-rich foods, adding isolated probiotic bacteria to a poorly fed gut is unlikely to produce meaningful results. Improving your prebiotic intake (through food first) will make any probiotic you take more effective.
Most people don’t need a standalone prebiotic capsule if they eat a varied diet of plant foods. Supplements are most useful when the diet has gaps, or when you want to pair a reliable prebiotic substrate with specific probiotic strains.
Getting All Three from Food
The most practical way to support pre-, pro-, and postbiotic activity is through diet rather than supplements.
Prebiotic foods to eat regularly: garlic, onions, leeks, chicory, Jerusalem artichokes, asparagus, slightly underripe bananas, oats, and flaxseed.
Probiotic foods that contain live cultures: plain live yoghurt, kefir, unpasteurised sauerkraut, kimchi, miso, and traditionally fermented cheeses.
Postbiotics are produced when the above are working well, though some traditionally fermented products also contain postbiotic compounds directly, as a result of the fermentation process.
The challenge is consistency. Eating adequate prebiotic fibre alongside regular fermented foods is difficult for many people, particularly those with food intolerances, restricted diets, or anyone following a low-FODMAP protocol where many prebiotic foods are temporarily off the table.
Supporting Your Gut with Biome Bliss
Biome Bliss is a naturally fermented gut supplement that delivers all three components in a single product. Six research-supported strains, including Lactobacillus plantarum, Lactobacillus rhamnosus, and Saccharomyces boulardii — are fermented in a base of organic honey, apple juice, and 25 organic herbs including raw ginger.
That base isn’t just a carrier. Honey contains oligosaccharides, apple juice provides pectin, and ginger and the herbs contribute fructooligosaccharides and other prebiotic compounds, so the bacteria are fermented alongside a natural prebiotic substrate, not freeze-dried in isolation.
The fermentation process produces organic acids and postbiotic metabolites, making the end product more closely aligned with a fermented food than with a standard capsule probiotic.
Frequently Asked Questions
What is the difference between prebiotics and probiotics?
Prebiotics are non-digestible fibres and compounds that feed beneficial gut bacteria. Probiotics are the live bacteria themselves. Prebiotics are the food; probiotics are the organisms that eat it. Both are needed for a healthy gut microbiome, and research shows they work most effectively together as a synbiotic combination.
Can you take probiotics and prebiotics together?
Yes, and taking them together tends to be more effective than either alone. This combination is called a synbiotic. Prebiotics provide the substrate that probiotic bacteria need to establish and multiply. If your diet is already rich in prebiotic foods, you may not need a separate prebiotic supplement, but pairing the two consistently improves outcomes (Swanson et al., 2020).
What do prebiotics do?
Prebiotics selectively feed beneficial bacteria in your gut, helping them grow and out-compete harmful microbes. This leads to increased production of short-chain fatty acids (postbiotics), improved mineral absorption, and better immune function. Common prebiotics include inulin, FOS, and GOS, found in foods like garlic, onions, oats, and legumes.
What are postbiotics and do I need to supplement them?
Postbiotics are the bioactive compounds produced when probiotic bacteria ferment prebiotic substrates, including short-chain fatty acids, organic acids, and other metabolites. You don’t generally need to supplement them separately. They are naturally produced when your gut bacteria are well-fed and active, or present in naturally fermented foods and supplements.
Is a synbiotic supplement better than a probiotic alone?
Research suggests yes. A 2020 ISAPP consensus paper confirmed that synbiotics (combining pre- and probiotics) produce more consistent benefits than probiotics taken without prebiotic support. The effect is strongest when the prebiotic is specifically matched to support the bacterial strains included in the product.
Should I take probiotics after antibiotics?
It depends. Research from the Weizmann Institute (Suez et al., 2018) found that standard multi-strain probiotics delayed native microbiome recovery by up to five months post-antibiotics. However, Saccharomyces boulardii has strong evidence for reducing antibiotic-associated diarrhoea specifically. Prebiotics and fermented foods may be a safer general approach to post-antibiotic gut recovery.
References
- Hill C et al. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nature Reviews Gastroenterology & Hepatology. 2014;11(8):506-514. PubMed
- Gibson GR et al. The ISAPP consensus statement on the definition and scope of prebiotics. Nature Reviews Gastroenterology & Hepatology. 2017;14(8):491-502. PubMed
- Suez J et al. Post-antibiotic gut mucosal microbiome reconstitution is impaired by probiotics. Cell. 2018;174(6):1406-1423. PubMed
- Swanson KS et al. The ISAPP consensus statement on the definition and scope of synbiotics. Nature Reviews Gastroenterology & Hepatology. 2020;17(11):687-701. PubMed
- Salminen S et al. The ISAPP consensus statement on the definition and scope of postbiotics. Nature Reviews Gastroenterology & Hepatology. 2021;18(9):649-667. PubMed
- Afzaal M et al. Human gut microbiota in health and disease: unveiling the relationship through probiotics, prebiotics, synbiotics, and postbiotics. Frontiers in Microbiology. 2025;13:999631. PMC
This article is for informational purposes only and does not constitute medical advice. If you have digestive symptoms or a health condition, speak to your GP before starting any new supplement.
