Interest in gut health and the human microbiome is booming, but the jargon can be confusing. In simple terms, probiotics are the live beneficial microbes we consume; prebiotics are the foods (mostly fibres) that feed those microbes; and postbiotics are the helpful by-products the microbes produce.

Think of making a sourdough starter: you add flour (the prebiotic food) and water to a jar. Wild yeasts and bacteria (the probiotics) begin to grow. Over days they ferment the flour, producing acids (the postbiotics like lactic acid) that make the starter sour. These acids help sustain a balanced microbial community. In your gut, a similar process happens – you eat plant fibres and polyphenols (prebiotics), which fuel beneficial microbes (probiotics). The microbes then produce short-chain fatty acids and other molecules (postbiotics) that support your health. A scientific consensus defines probiotics as “live microorganisms that… confer a health benefit” when eaten, prebiotics as “substrates that are selectively utilized by host microorganisms conferring a health benefit,” and postbiotics as preparations of non-living microbes or their components that benefit the host. 

Prebiotics – the “Fuel” for Beneficial Gut Bacteria

Prebiotics are typically plant-derived fibres and compounds that resist our own digestion but are fermented by gut microbes. They act like selective fertiliser for good bacteria such as Lactobacillus, Bifidobacterium and Akkermansia. Feeding these microbes helps them flourish, producing metabolites (like short-chain fatty acids) that reduce inflammation and nourish the gut lining. A broad range of prebiotic compounds exist, including inulin, fructo-oligosaccharides (FOS) and galacto-oligosaccharides (GOS). In practice, a diet high in varied plant fibres promotes microbial diversity, which is generally linked to better health. In contrast, low diversity (microbial “dysbiosis”) is associated with conditions like obesity, type 2 diabetes, inflammatory bowel disease and even mood disorders. 

Common sources of prebiotics include many whole plant foods. For example, inulin and related fructans in onions, garlic, leeks, asparagus or Jerusalem artichokes feed gut bacteria. Resistant starch found in cooked-and-cooled potatoes, rice and grains also arrives in the colon for microbes to ferment. Many pulses and legumes (beans, chickpeas, lentils), whole grains (oats, barley, wheat) and fibrous fruits (like green banana) are rich in prebiotic fibres. Even certain plant polyphenols (found in berries, tea, grapes, coffee, cacao and similar) can act like prebiotics: they survive digestion, reach the colon, and selectively boost helpful species (e.g. Akkermansia, Faecalibacterium, Bifidobacterium and Lactobacillus). Including these foods helps maintain a healthy, resilient gut ecosystem and supports immune and metabolic health. 

• Prebiotic Foods: Whole grains (oats, wheat, barley, rye), pulses and legumes (beans, lentils, chickpeas), vegetables like onions, garlic, leeks, asparagus, and chicory, bananas and other fruits.
• Polyphenol-rich Foods: Berries (blueberry, cranberry), red grapes, green tea/oolong, coffee, and cacao – plant compounds in these can feed and modulate gut bacteria.
• Fibre Targets: Aim to eat a variety of plants (leafy greens, nuts, seeds, herbs and spices) and at least 25–35 g of fibre daily. Western diets often fall short (around 15–20 g), so gradually increasing fibre (whole foods or added prebiotics) can boost diversity and bowel health. 

Probiotics - the "Live Cultures"

Probiotics are the living microbes (bacteria or yeasts) that can benefit our gut when we eat them in sufficient amounts. By occupying space and consuming nutrients, probiotics help crowd out pathogens and prevent infections. Many also produce lactic or other acids, which naturally inhibit harmful microbes and support the gut barrier. Importantly, probiotics aren’t generic – each strain has specific effects. For example, some Lactobacillus strains help relieve constipation or irritable bowel symptoms, others boost immune responses, and yet others have been linked to improved mood and blood sugar control. In short, probiotics are “team players” that add useful functions to your microbiome.

Clinically, dozens of trials show that probiotics can strengthen intestinal barrier function and reduce inflammation. A 2023 meta-analysis of 26 trials found that probiotic supplements significantly improved gut barrier measures (like tight-junction integrity) and lowered inflammatory proteins (CRP, TNF-α) in the blood. In the probiotic groups, beneficial bacteria (Bifidobacterium, Lactobacillus) also increased. This suggests everyday probiotics can calm gut inflammation and support immune balance. In practice, the easiest sources of probiotics are fermented foods. A ten-week study in healthy adults showed that eating more fermented foods (yogurt, kefir, kombucha, kimchi, sauerkraut, etc.) steadily increased gut microbial diversity and decreased blood inflammation. By contrast, a high-fibre-but-not-fermented diet did not change diversity in that short trial. In other words, regularly consuming fermented foods can “seed” your gut with a variety of friendly strains and their useful metabolic activities.

Fermented foods such as yogurt, kefir, sauerkraut and kimchi are rich sources of live probiotics. Probiotic effects are strain-specific, so for supplements look for products listing the scientific strain name (e.g. Lactobacillus plantarum Rosell-1012) and evidence-backed doses for your goal (e.g. immunity, mood, constipation).

• Fermented Probiotic Foods: Yogurt (especially with live cultures), kefir, probiotic cheeses; fermented vegetables (sauerkraut, kimchi, pickles); fermented soy (miso, tempeh); sourdough bread.
• Probiotic Supplement: Many multi-strain capsules are available. Choose one with well-studied strains such as Biome Restore and the CFU (colony-forming units) shown in trials. For example, certain strains help ease IBS, prevent traveller’s diarrhoea, or support vaginal health. Always follow product instructions for dosage.

Postbiotics - the "Afterlife" of Probiotics

Postbiotics are the beneficial by-products and components of probiotics, including short-chain fatty acids (SCFAs), peptides, cell wall fragments and even dead microbial cells. The ISAPP consensus defines a postbiotic as inactivated microbial cells (or their components) that still confer health benefits. In practice, this term highlights that probiotics’ metabolites can be as important as the live bacteria themselves.

Many of the best-known postbiotics are SCFAs, such as acetate, propionate and butyrate, which gut bacteria produce by fermenting fibre. These small molecules have powerful effects both locally and systemically. Locally in the gut, SCFAs reinforce the intestinal barrier and feed colon cells. They promote mucus and tight junction proteins, which keeps the gut lining healthy and prevents “leaky gut”. For example, butyrate has potent anti-inflammatory effects and directly strengthens barrier function. SCFAs also serve as an energy source for colon cells (providing up to 70% of their fuel) and modulate immune cells in the gut lining to maintain balance. 

Beyond the gut, postbiotics act as signalling molecules. They enter the bloodstream and can reach other organs, including the brain. Recent research describes SCFAs as key messengers in the gut–brain axis. For instance, acetate and propionate can influence satiety hormones and brain centres that regulate appetite, while butyrate may affect mood by increasing production of neurotrophic factors. In one study, butyrate even showed antidepressant-like effects in animal models. In the vaginal microbiome, lactic acid (a postbiotic of Lactobacilli) maintains an acidic environment that inhibits yeast infections and supports women’s health. In short, these “postbiotic” compounds help coordinate metabolism, immunity and even neurological health.

• How to get Postbiotics: The primary way is indirect – by eating prebiotics and probiotics. Feeding your microbiome a fibre-rich diet causes it to churn out SCFAs and other metabolites. Regularly eating fermented foods also delivers microbial metabolites along with the live cultures. In some cases, specific postbiotic supplements (like butyrate capsules) may be used, for example to help gut inflammation under medical guidance. Overall, a diet high in varied fibre and fermented foods is the best “recipe” to generate healthful postbiotics naturally. 

Biotic Shopping List (Gut-Healthy Diet Tips)

To optimise gut health through the “biotic” triad, aim for a diverse, plant-rich diet plus fermented foods:

• Variety of plants: Eat a rainbow of fruits, vegetables, whole grains, herbs and spices. Aim for many different plants each week (30 or more types) to supply varied fibres. This diversity feeds a diverse microbiome. Try to meet at least 25–35 g of fibre daily (much of it from vegetables, legumes, whole grains).
• Daily fermented foods: Include at least one serving per day of fermented/probiotic foods (yogurt, kefir, kombucha, sauerkraut, etc.). Clinical studies show that higher intake of fermented foods increases microbial diversity and lowers inflammation
• Phytonutrient-rich foods: Berries, greens, nuts, garlic/onion, tea, and cocoa are packed with polyphenols and antioxidants. These compounds have prebiotic-like effects (e.g. boosting Akkermansia and other keystone bacteria)
• Limit processed foods: Diets low in fibre (high in processed sugars/fats) tend to reduce beneficial bacteria. Minimising ultra-processed foods helps maintain a balanced microbiome.
• Mindful supplementation: Consider evidence-based supplements if needed (e.g. a researched probiotic strain for a specific issue, or a prebiotic fibre powder). But priority is food first.

Gut microbiome science is evolving rapidly, but the bottom line for wellness is clear: eating a variety of plant fibres and fermented foods feeds beneficial bacteria (prebiotics & probiotics) and yields valuable metabolites (postbiotics). This triad supports a resilient gut barrier and balanced immunity, which in turn promote overall health from digestion to mood. 

Sources: Authoritative reviews and clinical studies (see citations) outline the definitions and roles of prebiotics, probiotics and postbiotics, and their effects on human health. These sources include recent consensus statements and trials from high-impact journals.

Author: Dr Monika Stuczen, Medical Microbiologist