Prebiotics vs probiotics – what's the difference?

You've heard the words. They're on yoghurt pots, supplement bottles and wellness podcasts. But if someone asked you to explain the difference between a prebiotic and a probiotic — could you?

You're not alone if the answer is "not really." The terms sound similar, they're often mentioned together, and the marketing around both is so loud that the actual science can be hard to find.

Let's clear it up. Here's what prebiotics and probiotics are, how they work, why both matter for gut health, and when to be cautious.

What Are Probiotics?

Probiotics are live microorganisms — mainly bacteria and some yeasts — that, when taken in adequate amounts, can offer health benefits.

Think of them as the "friendly" residents of your gut. They're part of a vast community called the gut microbiome, which lives mainly in your large intestine and influences everything from digestion to immune function to mood.

Common probiotic types you'll see on labels include:

• Lactobacillus — found in yoghurt and fermented foods; may help with diarrhoea and lactose digestion
• Bifidobacterium — found in some dairy products; thought to support immune function
• Saccharomyces boulardii — a yeast probiotic studied for antibiotic-associated diarrhoea

Probiotics are found naturally in fermented foods like live yoghurt, kefir, kimchi, sauerkraut, miso and kombucha. They're also available as supplements.

The key thing to understand: probiotics are living organisms. They need to survive stomach acid to do their job. Not every strain works for every person, and effects are strain-specific — a strain that helps with IBS bloating won't necessarily help with something else.

What Are Prebiotics?

If probiotics are the friendly residents, prebiotics are their food.

Prebiotics are types of dietary fibre that your own digestive enzymes cannot break down. They pass through the small intestine largely intact and arrive in the colon, where gut bacteria ferment them. This produces short-chain fatty acids like butyrate, propionate and acetate — compounds that nourish the cells lining your gut, help regulate inflammation and support metabolic health.

Common prebiotic fibres include:

• Inulin — found in chicory root, Jerusalem artichokes, onions, garlic and leeks
• Fructo-oligosaccharides (FOS) — found in bananas, asparagus and some grains
• Galacto-oligosaccharides (GOS) — found in pulses, including lentils and chickpeas
• Resistant starch — found in cooked-and-cooled potatoes and rice, green bananas and oats

Prebiotics aren't alive, so they're stable in heat and on the shelf.

The key thing to understand: prebiotics feed the beneficial bacteria already in your gut. They don't add new species — they support what's already there.

Why Both Matter

Prebiotics and probiotics aren't rivals. They work together — which is why you'll sometimes see products labelled "synbiotic", meaning they combine both.

An easy way to remember it: probiotics are the seeds; prebiotics are the water and fertiliser. You can swallow billions of live bacteria, but if their food isn't there, they may not stick around for long.

Can You Just Get Them From Food?

For most people, yes — and food first is usually the best approach.

A diet rich in different plant foods (vegetables, fruit, pulses, wholegrains, nuts and seeds) naturally provides prebiotic fibres. Adding fermented foods supplies probiotics. Many experts suggest aiming for around 30 different plant foods a week to support a diverse microbiome.

Supplements can help in specific situations — for example, during or after a course of antibiotics, or when managing gut symptoms with professional guidance — but they're not a replacement for a varied diet.

A Simple Day of Pre- and Probiotics

• Breakfast: porridge oats with sliced banana and a spoon of live yoghurt
• Lunch: lentil and vegetable soup with wholegrain bread
• Snack: a small glass of kefir
• Dinner: stir-fry with leeks, onion and garlic, served with cooled-and-reheated rice and a spoon of kimchi

When to Be Cautious

Prebiotics and probiotics are generally safe for most people, but caution matters in some situations:

• IBS and FODMAP sensitivity: many prebiotic fibres are also high-FODMAP, which means they can trigger bloating, gas and discomfort in people with IBS. If you're following a low-FODMAP diet, check whether prebiotic foods or supplements are right for you. See our Low FODMAP Swap Guide.
• A severely weakened immune system: live probiotics may not be suitable for people who are severely immunocompromised. Always ask a medical professional first.
• Small intestinal bacterial overgrowth (SIBO): probiotics can sometimes worsen symptoms in active SIBO. Individual assessment is needed.
• Start low, go slow: if you increase fibre or fermented foods quickly, you may feel more bloated at first. Build up gradually and drink plenty of water.

The Bottom Line

Probiotics add friendly bacteria; prebiotics feed them. Together, they help your gut microbiome thrive. For most people, a varied, plant-rich diet with a little fermented food each day is the simplest place to start.

Want to know how your gut and mood are connected? Read The gut-brain connection – how your gut shapes your mood.

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This article is for educational purposes only and is not medical advice. Speak to your GP, pharmacist or a registered dietitian before starting supplements, especially if you have a health condition, are pregnant or take medication.