You’re standing in the health food aisle, surrounded by supplements making big promises. One jar says, “47 billion live cultures.” Another says it will “feed your microbiome.” A third uses a word you’ve never seen - postbiotic - and you’re not sure if it’s a real thing or a typo.
You put them all back and buy biscuits instead. Fair enough. But your gut is genuinely one of the most important systems in your body, and the difference between these three words - prebiotic, probiotic, postbiotic - actually matters. Here’s the simple version.
A quick tour of your gut
Deep in your digestive system lives a huge community of tiny organisms - mostly bacteria, plus some fungi and viruses (the friendly kind) - known as your gut microbiome. There are roughly 38 trillion of them in there. In a real sense, you’re more microbe than human.
These organisms aren’t just along for the ride. They help you digest food, support your immune system, produce vitamins, and even influence your mood - plus a lot of things scientists are still figuring out. Some researchers now call the gut microbiome a “forgotten organ,” which is a dramatic way of saying we’ve been ignoring something that’s been quietly keeping us alive all along.
When your microbiome is doing well, you tend to do well too. When it struggles - from poor diet, stress, antibiotics, or a rough patch involving too much wine and not enough vegetables - the effects can ripple across your whole body. Digestion problems, immune issues, low mood, tiredness, skin problems: many of these connect back to your gut.
That’s where prebiotics, probiotics and postbiotics come in. Think of them as three different ways of supporting the same community.
Probiotics: the new residents
Probiotics are live bacteria that, in the right amount, are good for you. In plain terms: living bugs you eat on purpose because they help.
You’ve probably eaten probiotics for many years without realising it - yoghurt, kefir, kimchi, sauerkraut, miso, kombucha are all full of live bacteria. Modern supplements package billions of specific bacteria strains into a capsule, usually from the Lactobacillus or Bifidobacterium families.
The catch: these bacteria have to survive manufacturing, shipping, storage, and then your stomach acid - which is roughly as acidic as battery acid - before they even reach your gut. Many don’t make it. Some studies suggest less than 1% of the bacteria in certain supplements arrive alive.
There’s also a less flattering truth: most probiotic bacteria don’t move in permanently. They pass through, do some good work, and leave. That’s fine - they can still help while they’re there - but it means you need to keep taking them to keep the benefit. Stop taking them, and the effect fades.
Think of probiotics as tourists visiting your gut. They boost things for a while, then head home. The town itself doesn’t fundamentally change.
Prebiotics: the food supply
If probiotics are the residents, prebiotics are what feeds them.
Prebiotics are types of fibre your body can’t digest - but your gut bacteria can. Your bacteria ferment this fibre and use it as fuel. The more you feed your good bacteria, the more they grow and crowd out the less helpful ones.
Common prebiotics include:
- Inulin - found in chicory root, garlic, onions and leeks
- FOS - found in bananas, asparagus and artichokes
- Beta-glucan - found in oats and barley
- Resistant starch - found in cooked-and-cooled potatoes and unripe bananas
A genuinely good diet, full of vegetables, legumes and wholegrains, already gives you plenty of prebiotic fibre. So if you eat well - properly well, not just now and then - you may not need a supplement. But most people don’t. The average Western diet is low in fibre and high in processed food. The UK recommends 30g of fibre a day; most adults only manage around 18g.
Prebiotics aren’t glamorous. No exciting names, no dramatic marketing. They’re just fibre. But without them, your gut bacteria are trying to run a kitchen with no food in it - no amount of good bacteria will help if there’s nothing for them to eat.
Postbiotics: the plot twist
This is where most people’s knowledge runs out - and where things get interesting.
Postbiotics are what bacteria produce after they’ve done their fermenting. Rather than eating live bacteria and hoping they survive long enough to help, postbiotics give you the results of that bacterial activity directly.
This includes things like:
- Short-chain fatty acids (like butyrate), which feed the cells lining your gut and reduce inflammation
- Enzymes that support digestion
- Peptides that support your immune system
- Vitamins, including B vitamins and vitamin K2
- Transformed plant compounds - where fermentation turns an ingredient into a richer, more absorbable version of itself
The word “postbiotic” is fairly new - officially defined by a scientific association in 2021 - but the idea is ancient. Every jar of miso, every bit of kimchi, every wheel of aged cheese is full of postbiotic compounds. We just didn’t have a name for it. We were doing it right all along without knowing why it worked.
The difference, in one picture
Imagine your gut is a brewery.
Prebiotics are the ingredients - the grain, the hops, the yeast food. No good ingredients, no good beer.
Probiotics are new brewers you bring in - skilled live workers. Some are great. Some don’t survive the journey. Some leave after a few weeks.
Postbiotics are the finished beer. You skip the question of “will the brewer survive?” and go straight to the product that actually does the work.
This is why postbiotics are exciting scientists right now. They’re stable (no living organism to keep alive), precise (you know exactly what’s in them), and often better absorbed - because fermentation has already done the hard work of turning raw ingredients into something your body can use.
Why fermented ingredients matter
When you ferment a plant - say, turmeric, or a mix of ingredients - something remarkable happens. The bacteria don’t just break the plant down. They transform it. Compounds your body couldn’t previously absorb become usable. New, different compounds are created that weren’t in the original plant at all.
Fermented turmeric, for example, doesn’t just give you curcumin. It gives you a whole range of new compounds, including one called tetrahydrocurcumin, which behaves differently - and often more usefully - than the original curcumin molecule. Fermentation essentially does some of your digestion for you, in advance.
This is the direction gut health science is heading: away from “take a probiotic and hope for the best,” and towards stable, well-understood postbiotic products that deliver consistent results.
Do you need all three?
Probably not all three as supplements - but ideally all three in some form.
Get your prebiotics from food. Eat plenty of garlic, onions, leeks, oats, bananas and legumes. If your diet is genuinely varied and plant-rich, you’re covered. If it isn’t - and most people’s aren’t - a supplement or a real effort to eat more fibre is worth it.
Get probiotics from fermented foods regularly, whether or not you also take a supplement. A daily serving of live yoghurt, kefir, or fermented vegetables gives you a broad range of good bacteria, plus naturally occurring postbiotic compounds - a more complex package than anything in a capsule. Probiotic supplements are especially useful after antibiotics (which wipe out good and bad bacteria alike), while travelling, or for specific digestive issues. But they can’t make up for a poor diet.
Postbiotics are where the most interesting supplement innovation is happening. If you’re standing at the shelf wondering what’s actually worth buying, a well-researched postbiotic product - especially one based on fermented ingredients with real clinical evidence - is a genuinely strong option. Stable, consistent, well-absorbed, and not dependent on a tiny organism surviving your stomach acid.
The short version
Prebiotics feed your good bacteria - get them from plants. Probiotics are live bacteria that help while they’re passing through - get them from fermented food or supplements. Postbiotics are the beneficial compounds bacteria produce, and they’re arguably the most exciting area in gut health science right now.
None of these is a magic fix. All of them matter. And none of them will do much if you’re living on processed food and four hours of sleep. Your gut is a system, not a slot machine.
Your microbiome has been quietly running one of the most complex ecosystems on Earth for your entire life, mostly without your help. The least you can do is learn its language - and maybe put the biscuits down. At least some of the time.
By Alastair Jessel, The Postbiotic Company. Adapted from our writings on Substack.
