Prebiotics, Probiotics, Synbiotics & Postbiotics: What’s the Difference?
If you’ve been looking into gut health lately, you’ve probably come across the words prebiotics, probiotics, synbiotics and postbiotics. They’re popping up everywhere, from yoghurt tubs and fermented foods to supplements and wellness trends.
But what do they actually mean? How do they work, and do you need to be adding them to your diet?
Let’s break down the science behind these four gut health buzzwords, what they do in your body, and some practical ways to support your gut microbiome through everyday food choices.
First, what is the gut microbiome?
Your gut is home to trillions of microorganisms, including bacteria, fungi and other microbes. Together, these form your gut microbiome: a diverse community that plays an important role in your health.
It’s a two-way relationship: you provide these microbes with nourishment, and they help break down certain types of fibre that your body cannot digest on its own. In doing so, they produce compounds such as short-chain fatty acids (SCFAs), which help support the gut lining, influence immune function and contribute to a healthy gut environment. This beneficial co-existence is also known as a symbiotic relationship (just to make things more confusing).
Your gut microbiome also interacts with your immune system and helps maintain the intestinal barrier. Research is continuing to explore how the microbiome influences other aspects of health, including metabolism and the gut–brain connection.
Your microbiome is unique to you and influenced by factors including:
Diet: food variety and fibre intake
Medications: particularly antibiotics
Early life: birth, infant feeding and early exposures
Lifestyle: sleep, movement and stress
Genetics & environment: your age, genes and surroundings
While you can’t control every factor, your everyday habits can help create an environment where a diverse community of microbes can thrive. The goal isn’t to eliminate every “bad” bacteria or chase a specific bacterial count. Instead, it’s about supporting a diverse, functioning microbial community.
And that’s where prebiotics, probiotics, synbiotics and postbiotics come in.
1. Prebiotics: food for your gut microbes
Think of prebiotics as fuel for certain beneficial microorganisms living in your gut.
Prebiotics are substances, usually specific types of dietary fibre, that are selectively used by microorganisms in the body and provide a health benefit. Your body doesn’t fully digest these fibres, allowing certain gut microbes to use them.
As these microbes ferment prebiotic fibres, they can produce beneficial compounds, including SCFAs.
Why do they matter?
Depending on the type of prebiotic and the microbes involved, they may help support:
A healthy gut environment and intestinal barrier.
Regular bowel movements and stool consistency.
The production of beneficial compounds, such as butyrate.
The growth or activity of specific beneficial gut microbes.
Where can you find prebiotics?
You don’t necessarily need a supplement. Many everyday foods contain prebiotic fibres or other fermentable carbohydrates that your gut microbes can use.
Some examples include:
Oats and barley.
Onions, garlic and leeks.
Asparagus and chicory root.
Slightly green bananas.
Legumes, including chickpeas, lentils and beans.
Cooked and cooled potatoes or rice, which can contain resistant starch.
Different fibres feed different microbes, so variety is helpful.
Dietitian tip: Increase fibre gradually and drink enough fluid. A sudden jump in fibre intake can cause bloating, wind or changes in bowel habits, particularly if you have IBS or a sensitive gut. You don’t need to force yourself to eat every food on this list to support your microbiome.
2. Probiotics: live microorganisms that can offer a health benefit
Probiotics are live microorganisms that, when administered in adequate amounts, provide a health benefit to the person taking them.
You might have heard that probiotics are simply “good bacteria”, but there’s a little more to it. Not every microorganism is a probiotic, and not every product containing live cultures has a proven health benefit.
Why do they matter?
Certain probiotic strains have been studied for specific health outcomes, including:
Helping reduce the risk of antibiotic-associated diarrhoea in some circumstances.
Supporting the management of certain types of diarrhoea.
Improving some symptoms of specific digestive conditions in selected people.
However, the evidence varies considerably. A probiotic that helps with one condition may not help another, and benefits demonstrated for one strain cannot automatically be applied to every product in the same category.
Probiotics also don’t necessarily permanently colonise your gut. Their effects may depend on the strain, dose, duration of use and individual.
Where can you find probiotics?
Some fermented foods contain live microorganisms, including:
Yoghurt with live cultures.
Kefir.
Some fermented vegetables, such as unpasteurised sauerkraut or kimchi.
Certain other fermented foods, depending on how they are produced and processed.
Not all fermented foods contain live microorganisms by the time you eat them, and not all foods containing live cultures meet the scientific definition of a probiotic.
Probiotic supplements are another option, but choosing one should depend on the reason for taking it, the specific strain and the evidence supporting its use.
Dietitian tip: More strains or a higher CFU count (colony-forming units) doesn’t automatically mean a better probiotic. Look for evidence relevant to your particular health concern rather than choosing a supplement based on the biggest number on the label.
3. Synbiotics: prebiotics and probiotics working together
A synbiotic combines live microorganisms with a substrate that is selectively used by microorganisms in the body and provides a health benefit.
In simple terms, it brings together a probiotic and a prebiotic in one approach.
The idea is that the combination may offer benefits by introducing specific live microorganisms while also providing a substance that supports microbial activity.
There are two broad types:
Complementary synbiotics: A probiotic and a prebiotic are combined to provide their respective benefits, without necessarily needing to work together.
Synergistic synbiotics: The prebiotic component is specifically selected to be used by the co-administered live microorganism.
Where can you find synbiotics?
Breast milk is a natural synbiotic (containing human milk oligosaccharides and Bifidobacteria). Some supplements and formulated foods are designed as synbiotics, with selected probiotic strains and prebiotic ingredients such as inulin or fructooligosaccharides (FOS).
Some products marketed for gut health may contain both ingredients, but that doesn’t automatically mean the combination has been shown to deliver a health benefit.
Do you need a synbiotic supplement?
Not necessarily. A varied diet that includes fibre-rich plant foods can support your existing gut microbes, while particular probiotic products may be useful for specific indications. Combining them isn't automatically better than using either alone.
If you have IBS, be aware that some prebiotic ingredients, including inulin and FOS, can trigger symptoms such as bloating, gas or abdominal discomfort in sensitive individuals.
4. Postbiotics: the products and substances left behind by your microbes that have beneficial effects
Postbiotics are preparations of inanimate microorganisms and/or their components that confer a health benefit.
Put simply, they involve non-living microorganisms or their components in a preparation that has been shown to provide a benefit.
You may also hear about metabolites — substances produced by microbes as they break down food. These include SCFAs such as acetate, propionate and butyrate.
Why do they matter?
Some postbiotics have been investigated for their potential to:
Support the intestinal barrier.
Interact with immune function.
Influence gut function and digestive symptoms.
However, research is still developing, and findings from one product cannot be applied to all postbiotics.
Where can you find postbiotics?
Postbiotics are increasingly appearing in formulated foods and supplements. They may contain inactivated microorganisms or microbial components that have been prepared for a particular purpose.
But… you don’t need to buy a postbiotic supplement to support your gut health. Eating a varied diet with adequate fibre helps your gut microbes produce useful metabolites naturally, although these food-derived compounds are not necessarily classified as postbiotics themselves.
So, what’s the best way to support your gut microbiome?
You don’t need an expensive supplement routine or a perfectly curated gut health pantry.
For most people, start with the basics:
1. Eat a variety of plant foods.
Fruit, vegetables, wholegrains, legumes, nuts and seeds provide different types of fibre and other compounds that help nourish your gut microbes. Variety across the week is a useful goal — and you can build it gradually.
2. Include fibre-rich foods regularly.
Oats at breakfast, lentils in a soup, chickpeas in a salad or vegetables alongside dinner all count. Small additions can make a difference over time.
3. Enjoy fermented foods if you like them.
Yoghurt with live cultures, kefir, kimchi and some fermented vegetables can be enjoyable additions to a balanced diet. They aren't essential, and fermented doesn't always mean probiotic.
4. Increase fibre at a pace that suits your gut.
If you experience bloating, constipation or IBS symptoms, adding lots of fibre or prebiotic supplements all at once may make things worse. Start with manageable amounts and adjust to your tolerance.
5. Be selective with supplements.
Probiotics, synbiotics and postbiotics aren't one-size-fits-all. Before spending money on a supplement, consider what you're hoping to improve and whether there is good evidence for that specific product and outcome. A dietitian or other qualified health professional can help you navigate the options.
The bottom line
Prebiotics help feed specific gut microbes. Probiotics are live microorganisms that provide a health benefit. Synbiotics combine live microorganisms with beneficial substrates, and postbiotics are preparations of inanimate microorganisms and/or their components that provide a health benefit.
They each have a different role, and none is a magic fix for every gut concern.
The good news? You can support your gut microbiome without making food complicated. A varied, fibre-rich diet, tailored to your individual needs and tolerance, is a great place to start.
Want personalised advice for bloating, bowel changes or other digestive symptoms? An Accredited Practising Dietitian can help you work out which dietary strategies are appropriate for you, without unnecessary food restriction.
Further Readings & References:
International Scientific Association for Probiotics and Prebiotics (ISAPP) — consensus definitions for prebiotics, probiotics, synbiotics and postbiotics.
Monash University — practical information about FODMAPs, fibre and IBS, particularly relevant to readers who experience bloating.
National Center for Complementary and Integrative Health — evidence and safety considerations for probiotics.