Between 100 and 500 trillion microorganisms live in your gut – more than there are cells in your entire body. This invisible community governs immunity, mood, metabolism, and the pace of ageing. Prebiotics vs probiotics – these are two different tools for shaping it, and they work in fundamentally different ways. Find out which one your microbiome actually needs.
Key facts about prebiotics and probiotics:
- Prebiotics are food for bacteria – fibre and other compounds you don’t digest, but your bacteria do
- Probiotics are live microorganisms that, when given in adequate amounts, provide a health benefit
- Synbiotics combine both in a single product or meal
- Natural sources often support the microbiome more effectively than capsules
- Microbiome needs change with age – what worked at 30 may be insufficient after 60
What are prebiotics and what are probiotics?
Prebiotics are substances – most often dietary fibre or oligosaccharides – that the human body doesn’t digest, but which are fermented by gut bacteria. The best-studied are inulin and FOS (fructooligosaccharides), found in onions, garlic, chicory, and bananas. When bacteria ferment prebiotics, they produce short-chain fatty acids (SCFAs) – compounds that nourish gut cells and help regulate inflammation.
Probiotics are live bacteria or yeasts that, when given in adequate amounts, provide a health benefit. The most common are strains of Lactobacillus and Bifidobacterium. Unlike prebiotics, probiotics don’t “feed” existing bacteria – they temporarily colonise the gut, supporting microbiome balance for as long as they’re present.
What are synbiotics and how do they support gut flora?
Synbiotics combine prebiotics and probiotics in a single formula or food. The prebiotic acts as fuel for the probiotic bacteria, improving their survival in the digestive tract and aiding colonisation of the large intestine. A natural example is kefir with banana or yoghurt with flaxseed.
The table below summarises the key differences between the two – where to find them and when each one makes more sense.
Prebiotics vs probiotics – key differences:
| Prebiotics | Probiotics | |
| What they are | Fibre and complex sugars – fuel for bacteria | Live bacteria or yeasts |
| How they work | Feed the bacteria you already have | Colonise the gut temporarily |
| Sources | Onion, garlic, bananas, leeks, chicory | Kefir, yoghurt, sauerkraut, kimchi |
| Effect | Long-lasting – strengthens the existing microbiome | Temporary – disappears after you stop consuming them |
| Best for | People with a rich microbiome | People after antibiotics or with depleted flora |
Prebiotics vs probiotics – which are more powerful?
Probiotics add new strains – but work mainly temporarily. Prebiotics nourish existing bacteria. The Sonnenburg lab at Stanford (Cell, 2021) found that fermented food more effectively diversified the microbiome and lowered inflammatory markers than a high-fibre diet in people with depleted microbiota. In those with a rich microbiome, fibre worked better.
If your microbiome has been depleted by antibiotics or stress, probiotics may deliver a faster effect. For long-term maintenance, an adaptive diet rich in prebiotics does more good than capsules. You don’t need to choose.
How do probiotics affect the gut microbiome in older people?
Probiotics in older people improve immune function and reduce the severity of antibiotic-associated diarrhoea – though effects are strain-specific. Claesson and colleagues (Nature, 2012) examined 178 older adults in Ireland and found those in care homes had significantly less diverse microbiota and worse inflammatory markers than peers living independently.
Probiotic supplementation with beneficial strains in people over 60 is linked to improved immunity and reduced antibiotic-associated diarrhoea. Effects are strain-specific though – not every probiotic works the same way.
What are the best natural sources of prebiotics?
Natural prebiotic sources:
- Chicory and chicory root – the highest inulin concentration among widely available foods
- Garlic and onion – FOS and inulin, easily accessible and versatile in cooking
- Leek and asparagus – a milder flavour with a similar prebiotic profile
- Slightly underripe bananas – contain resistant starch, which ferments more slowly than FOS
- Oats and sourdough rye bread – beta-glucan and arabinoxylan (types of prebiotic fibre) supporting lactic acid bacteria
How much fibre does the microbiome need daily?
Recommendations call for 25-30 g of dietary fibre per day – a bowl of porridge, a handful of vegetables, and a slice of rye bread. The average person gets around 15-16 g daily, which is too little. Increasing daily fibre to 30 g over four weeks boosts beneficial gut bacteria. People in Blue Zone longevity regions consume 40-50 g of fibre daily.
Where to get probiotics – Lactobacillus and other strains
The best source of probiotics is fermented food. It delivers live bacteria in a natural food matrix, improving their survival – and adds organic acids, enzymes, and B vitamins. Yoghurt, kefir, buttermilk, sauerkraut, kimchi, and miso are practical, everyday sources of diverse strains.
A practical guide to strains:
- Lactobacillus acidophilus – mainly in yoghurts and fermented dairy drinks
- Bifidobacterium longum – fermented dairy products, supports immune function
- Lactobacillus plantarum – fermented vegetables (sauerkraut, pickles, kimchi)
- Saccharomyces boulardii – fermented products, often used after antibiotics
- Lactobacillus rhamnosus GG – functional yoghurts, one of the best-studied strains
The more types of fermented products you include each week, the broader your natural probiotic supplementation. More on how specific foods affect microbiome composition: fermented products in the diet.
When to supplement prebiotics vs probiotics, and when is diet enough?
A healthy person eating a varied plant-based diet typically doesn’t need supplements. Vegetables, fermented foods, and whole grains are usually enough. Supplements make sense after antibiotics or with irritable bowel syndrome. A longevity diet is built on plant variety, not capsules.
FAQ: Frequently asked questions about prebiotics and probiotics
What is the difference between prebiotics and probiotics?
Prebiotics are indigestible dietary fibre that feeds beneficial gut bacteria, while probiotics are live microorganisms that temporarily colonise the gut and directly influence the microbiome’s composition.
Is yoghurt a sufficient source of probiotics?
Natural yoghurt with live cultures delivers several Lactobacillus and Bifidobacterium strains, which with regular consumption provides meaningful microbiome support, though it won’t replace the broader diversity offered by a range of fermented foods.
Is it better to take prebiotics and probiotics together?
Combining both – synbiotics – can improve probiotic bacteria survival because the prebiotic provides fuel for them, though for people with sensitive guts it’s worth introducing each one gradually.
What does research tell us about seniors?
Studies show that microbiome diversity declines with age, and probiotic supplementation in older adults may improve immune function and reduce antibiotic-associated diarrhoea, though effects are strain-specific and don’t work identically for everyone.
If you have a specific condition or take medication, discuss supplement choices with your doctor.
References:
- Sonnenburg, J. L., et al. (2021). Gut-microbiota-targeted diets modulate human immune status. Cell. https://doi.org/10.1016/j.cell.2021.06.019
- Claesson, M. J., et al. (2012). Gut microbiota composition correlates with diet and health in the elderly. Nature. https://doi.org/10.1038/nature11319
- Dahl, W. J., & Stewart, M. L. (2015). Position of the Academy of Nutrition and Dietetics: Health Implications of Dietary Fiber. Journal of the Academy of Nutrition and Dietetics. https://doi.org/10.1016/j.jand.2015.09.003
