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Probiotics vs Prebiotics: What's the Difference?

By Claire Hartley  ·  Updated June 13, 2025

By Claire Hartley · · 8 min read
Quick answer Probiotics are beneficial live bacteria (found in fermented foods like yoghurt, kefir, and unpasteurised sauerkraut). Prebiotics are dietary fibres that feed your existing gut bacteria (found in garlic, onion, oats, and slightly green bananas). They work together — and for most healthy adults, food provides both without the need for supplements.
Quick answer: Probiotics are beneficial bacteria; prebiotics are the fibre that feeds them. Get probiotics from live-culture yoghurt, kefir, and unpasteurised fermented vegetables; get prebiotics from garlic, onion, oats, bananas, legumes, and wholegrains. They work together, and a bowl of yoghurt with oats and banana provides both — supplements aren't necessary for most healthy adults.

Probiotics and prebiotics sound almost identical, get marketed interchangeably, and confuse almost everyone. But they're fundamentally different things — and understanding the difference is genuinely useful when you're trying to support your gut through food.

This guide explains what each one is, how they work together, which foods provide them, and whether you actually need supplements.

The simple distinction

Here's the difference in one sentence: probiotics are the beneficial bacteria themselves; prebiotics are the food that feeds them.

Think of your gut as a garden. Probiotics are like planting new seeds — adding beneficial bacteria. Prebiotics are the fertiliser — the fibres that nourish the bacteria already living there. Both matter, and they work best together.

The key principle
You don't have to choose between them. A varied diet naturally provides both. The goal isn't to chase one or the other — it's to eat in a way that both introduces beneficial bacteria and feeds the ones you already have.

Probiotics: the beneficial bacteria

Probiotics are live microorganisms that, in adequate amounts, may confer a health benefit. You get them primarily through fermented foods that contain live cultures.

Food sources of probiotics

Live-culture yoghurt and kefir

The most accessible sources. Kefir typically has a higher diversity of cultures than yoghurt.

Unpasteurised sauerkraut and kimchi

Fermented vegetables with live cultures — as long as they're refrigerated and not heat-treated.

Miso, tempeh, and some other fermented foods

Fermented soy products that contribute beneficial cultures (though miso is high in salt).

Our beginner's guide to fermented foods covers how to introduce these without upsetting your system.

Prebiotics: the food for your bacteria

Prebiotics are types of dietary fibre that human digestion can't break down — but that your gut bacteria ferment and thrive on. In other words, they feed the beneficial bacteria already in your gut. The Harvard Health guidance notes that feeding existing gut bacteria with prebiotic fibre is at least as important as adding new bacteria through probiotics.

Food sources of prebiotics

Garlic, onion, and leeks

High in inulin and fructooligosaccharides (FOS), two of the best-studied prebiotic fibres. They form the flavour base of countless meals.

Slightly green bananas

Higher in resistant starch, which acts as a prebiotic. Less ripe bananas have more than fully ripe ones.

Oats

Contain beta-glucan, a soluble fibre with prebiotic properties — and one of the most affordable gut-friendly foods.

Asparagus, legumes, and wholegrains

All provide prebiotic fibres. Variety is key — different fibres feed different bacterial populations.

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How they work together

Probiotics and prebiotics are complementary. Adding beneficial bacteria (probiotics) is more effective when those bacteria have something to eat (prebiotics). This is why products that combine both are sometimes called "synbiotics."

But you don't need a special product to get the combination. A breakfast of live-culture yoghurt (probiotic) with oats and a slightly green banana (prebiotics) delivers both in one bowl. That's the food-first approach in action: real food, doing two jobs at once.

Do you need supplements?

This is where marketing gets ahead of the evidence. You'll see probiotic capsules and prebiotic powders marketed as essential gut-health solutions. For most generally healthy adults, they're not.

For most people starting from a general dietary baseline, food-first sources produce more consistent results than supplements — and you get the additional benefits of whole foods (fibre variety, nutrients, lower cost) at the same time. Supplements can have a role in specific circumstances, particularly under professional guidance, but they're best seen as a complement to good dietary habits rather than a replacement.

A balanced takeaway
Don't overthink the probiotic-versus-prebiotic question. Eat a variety of plant foods (prebiotics) and include some fermented foods with live cultures (probiotics). That covers both, affordably, without needing to decode supplement labels.

The Supplement Education Guide included in the 21-Day Gut Reset covers probiotic and prebiotic supplements in plain English — explaining what the evidence does and doesn't support, without pushing any specific product.

Frequently asked questions

What's the difference between probiotics and prebiotics?
Probiotics are beneficial live bacteria, found mainly in fermented foods with live cultures. Prebiotics are types of dietary fibre that feed the bacteria already in your gut, found in foods like garlic, onion, oats, and slightly green bananas. Probiotics add bacteria; prebiotics feed them.
Which is more important, probiotics or prebiotics?
Neither is more important — they work together and complement each other. Adding beneficial bacteria works better when those bacteria have prebiotic fibre to feed on. A varied diet naturally provides both, so there's no need to prioritise one over the other.
Can I get probiotics and prebiotics from food?
Yes, and for most healthy adults food is the best source. Probiotics come from live-culture yoghurt, kefir, and unpasteurised fermented vegetables; prebiotics come from garlic, onion, oats, bananas, legumes, and wholegrains. A bowl of yoghurt with oats and banana provides both.
Do I need to take probiotic or prebiotic supplements?
For most generally healthy adults, no. Food-first sources produce more consistent results than supplements and provide additional benefits like fibre variety and nutrients. Supplements can have a role in specific circumstances under professional guidance, but they're a complement to good diet, not a replacement.
What are synbiotics?
Synbiotics are products that combine both probiotics and prebiotics, on the principle that beneficial bacteria work better when supplied with food. You don't need a special product to get the combination, though — pairing fermented foods with prebiotic-rich foods does the same thing.
Claire Hartley

Written by Claire Hartley

Wellness writer and food-first digestive health researcher based in Melbourne, Australia. Author of the 21-Day Gut Reset. Read more about Claire →