Prebiotics, probiotics and postbiotics: How each may support gut and immune health

Learn what prebiotics, probiotics and postbiotics are, how they differ, and how each may support gut and immune health. Evidence-based guide from Blackmores.

Walk past any pharmacy shelf and you'll see probiotics, prebiotics and postbiotics positioned around gut and immune health. The terms sound similar but describe three different things, each playing a different role in how the gut and its resident microbes interact with the rest of the body. Understanding what each one is can make navigating the category easier.

This guide covers what prebiotics, probiotics and postbiotics actually are, how each interacts with the gut, and how each is being studied in relation to gut and immune health.

What are prebiotics, probiotics and postbiotics?

These three categories sit within the broader field of "biotics", a group of substances that interact with the gut microbiome in different ways. The International Scientific Association for Probiotics and Prebiotics (ISAPP) has issued formal consensus definitions for each.

Prebiotics, probiotics and postbiotics have all been formally defined by the International Scientific Association for Probiotics and Prebiotics (ISAPP) through a series of consensus statements published in Nature Reviews Gastroenterology & Hepatology between 2014 and 2021. Each definition has been refined as the science has matured, with postbiotics the most recent addition to the category.

The link between the gut and the immune system

The gut is more than a digestive organ. A review in Clinical & Experimental Immunology estimated that around 70% of the body's immune cells reside in gut-associated lymphoid tissue. This makes the intestinal lining one of the largest interfaces between the immune system and the outside world.

The trillions of microbes living along this lining, collectively known as the gut microbiota, interact constantly with immune tissue. A review by Nutrients described how a balanced gut microbiota contributes to the maturation of immune cells, supports the integrity of the gut barrier, and plays a role in the body's response to pathogens. When that microbiota is disrupted, this regulatory function can be affected.

This is the reason prebiotics, probiotics and postbiotics have attracted research interest in immune health: each one, in different ways, can influence the make-up or activity of the gut microbiota.

How probiotics may support gut and immune health

Probiotics are live microbes, typically strains of Lactobacillus or Bifidobacterium, that can transiently colonise the gut. Mechanisms by which they may interact with the immune system include competing with potentially harmful bacteria for space and nutrients, producing compounds that lower gut pH, and influencing signalling between immune cells.

A Cochrane systematic review examined 12 randomised trials covering more than 3,700 participants and found that probiotics may be better than placebo at reducing the number of people experiencing acute upper respiratory tract infections. The authors noted the certainty of the evidence as low to moderate, and benefits varied by strain and population, so the findings should be interpreted with this in mind.

Effects of probiotics also depend on dose, duration of use, and the individual's existing microbiota. Strain specificity is one of the most consistent themes in the research, meaning results from one probiotic strain cannot be assumed for another.

How prebiotics may support gut and immune health

Prebiotics are types of dietary fibre that the human body cannot digest, but that resident gut bacteria can ferment. This fermentation feeds beneficial microbes such as bifidobacteria and produces short-chain fatty acids (SCFAs) like butyrate, acetate, and propionate.

A review by Foods described how SCFAs contribute to the integrity of the intestinal barrier and play a role in regulating immune cell activity. Common dietary prebiotics include inulin, fructo-oligosaccharides (FOS), and galacto-oligosaccharides (GOS).

The evidence for prebiotic supplementation directly affecting human immune outcomes is still developing. Results have varied across studies based on prebiotic type, dose, and population. Foods naturally rich in prebiotic fibres include garlic, onion, leek, asparagus, slightly under-ripe banana, oats, legumes, and Jerusalem artichoke.

How postbiotics may support gut and immune health

Postbiotics are the newest category in this space. They include inactivated microbial cells, fragments of microbial cells, and metabolites produced by microbes during fermentation. A familiar example is yeast cell wall extract derived from Saccharomyces cerevisiae, which contains beta-glucan and other cell wall components and is used in some immune-support formulations.

The 2021 ISAPP consensus paper defined postbiotics formally and outlined how, because they don't contain live organisms, they may have practical advantages such as greater stability and a more predictable composition. Examples include heat-treated Lactobacillus preparations and short-chain fatty acids generated through fermentation.

Research on postbiotics for immune health is still emerging. Early-stage evidence suggests postbiotic preparations may interact with gut immune cells in ways comparable to live probiotics, though larger human trials are needed before firm conclusions can be drawn.

Key differences explained simply

A practical way to remember the difference: probiotics are the live workers, prebiotics are the food the workers eat, and postbiotics are the products that result from the work.

Each interacts with the gut microbiota in a different way:

• Probiotics introduce live microbes that may temporarily add to the existing population.
• Prebiotics nourish the microbes already living in the gut.
• Postbiotics provide beneficial substances that microbes would otherwise produce themselves.

This distinction matters because the strength of evidence, the populations studied, and the practical considerations (storage, shelf life, dosing) differ across the three.

How prebiotics, probiotics and postbiotics work together in the gut

Although these are distinct categories, they sit within the same biological loop. Prebiotic fibres are fermented by gut bacteria, including probiotic strains, and that fermentation produces postbiotic compounds such as short-chain fatty acids.

Live microbes act on the substrate, and the metabolic outputs go on to interact with intestinal cells, immune cells, and the broader microbial community. Combinations of probiotics and prebiotics, sometimes called synbiotics, are studied for their potential complementary effects.

Do you need all three for gut support?

Not necessarily. For most people, supporting the gut microbiota starts with diet. A study by mSystems, found that participants who ate more than 30 different plant foods per week had a more diverse gut microbiota than those who ate fewer than 10. Plant diversity provides a range of fibres, polyphenols, and natural prebiotic compounds that feed different microbial groups.

Whether supplementing with one, two, or all three categories suits your needs depends on individual goals, dietary patterns, and any underlying health considerations. There is no single right answer, and a healthcare professional can help assess individual needs.

Food versus supplementation: what to consider

Both food and supplements can play a role in gut health, and they tend to work best together rather than as substitutes.

Food sources of probiotics: yoghurt with live cultures, kefir, kimchi, sauerkraut, miso, tempeh, and some aged cheeses.

Food sources of prebiotics: garlic, onion, leek, asparagus, slightly green banana, oats, barley, legumes, apples, and Jerusalem artichoke.

Sources of postbiotic compounds: fermented foods naturally contain microbial metabolites and inactivated cells, so foods like sauerkraut, kefir, miso, and aged cheeses contribute postbiotic compounds alongside live cultures.

Supplements may be considered when dietary intake is inconsistent, when a specific strain or compound has been studied for a particular use, or when convenience matters. Quality varies between products, so look for clear strain labelling (for probiotics), measured doses (for prebiotics), and transparent ingredient lists (for postbiotics).

Choosing a gut health approach that suits your needs

When considering a supplement in this space, a few practical questions can help guide the decision:

• What is the goal? General gut support, immune support, travel-related digestive support, and post-antibiotic support are different use cases.
• Is the strain or ingredient specified, with a measured dose? Generic "probiotic blend" labels with no strain detail offer less clarity.
• Does the product require refrigeration, or is it shelf-stable? This affects practicality.
• What does the existing diet already provide? Someone already eating fermented foods and a wide range of plants may benefit from a different approach than someone with a more limited diet.

Blackmores Gut Immune Biotic is formulated with Saccharomyces cerevisiae yeast cell wall extract alongside vitamin C and zinc. The yeast cell wall component is an example of a postbiotic-style ingredient (a preparation derived from inactivated microbial cells), while vitamin C and zinc are nutrients with established roles in normal immune function. It is intended for adults and is not to be used in children. Whether a postbiotic-based, probiotic, prebiotic, or combination approach suits an individual depends on context and personal preference.

When to speak with a healthcare professional

Most healthy adults can include probiotic and prebiotic foods as part of a balanced diet without concern. People who are immunocompromised, who have a serious underlying illness, who are pregnant or breastfeeding, or who are managing complex medications may have additional considerations and can benefit from speaking with a healthcare professional before starting supplements in this category. The Therapeutic Goods Administration (TGA) regulates these products in Australia, and labels should always be read carefully.

Frequently asked questions

What is the best probiotic for the immune system?

There is no single "best" probiotic for immune support. The Cochrane review found that benefits for upper respiratory tract infections varied by strain, dose and population. Look for products that specify the strain and dose, and consider speaking with a healthcare professional about what may suit your situation.

Do prebiotics help immunity?

Prebiotics are fermented in the gut to produce short-chain fatty acids, which a review by Foods described as contributing to gut barrier integrity and immune cell regulation. Direct human evidence for immune outcomes is still developing, with results varying by prebiotic type and population.

What are postbiotics and how do they work?

Postbiotics are non-living microbial preparations or their components, defined in the ISAPP consensus paper. They include short-chain fatty acids and heat-treated bacterial cells, and they may interact with gut and immune cells in ways comparable to live probiotics. Larger human trials are needed before firm conclusions can be drawn.

Can you take prebiotics and probiotics together?

Yes. Prebiotic fibres are the substrate that probiotic and resident gut bacteria can ferment, so combining them, sometimes called a symbiotic approach, is recognised in research, though benefits vary by formulation.

Do I need to take all three?

Not necessarily. A varied, plant-rich diet with some fermented foods provides prebiotic fibres, live microbes, and natural postbiotic compounds. Supplementation may be considered when dietary intake is limited or when targeting a specific use case.

Key takeaways

Prebiotics, probiotics and postbiotics are three connected but distinct categories. Probiotics are live microbes, prebiotics are the fibres that feed gut bacteria, and postbiotics are the compounds and inactivated microbial components that result from microbial activity. Each has been studied for its interaction with the gut microbiota and, by extension, with the gut-associated immune tissue.

The strongest gut health foundation comes from a varied diet rich in plants and fermented foods. Supplementation may suit specific goals or dietary gaps, and product quality varies, so labels and strain detail are worth reading carefully.

Always read the label and follow the directions for use.

Disclaimer: This article provides general information only and is not intended to diagnose, treat, cure, or prevent any disease. The information presented is not a substitute for professional medical advice. If you have concerns about your health, please consult your GP or healthcare provider for a personalised assessment and recommendations. Supplements should not replace a balanced diet.