Most people know they should eat more fibre. But the type of fibre matters as much as the amount — and specifically, whether it’s prebiotic: meaning fermentable by your gut bacteria to produce compounds that support gut health.
Here’s a complete guide to prebiotic foods, how they work, and how to get more of them without upsetting your digestive system.
How prebiotics work
Prebiotic compounds — primarily certain fibres and resistant starches — pass undigested through the small intestine and reach the colon, where they’re fermented by resident bacteria. This fermentation produces short-chain fatty acids (SCFAs) — particularly butyrate, propionate, and acetate.
Butyrate is the primary fuel source for colonocytes (the cells lining the colon). It also has anti-inflammatory properties, supports gut barrier integrity, and has been linked to reduced colon cancer risk. Propionate and acetate enter the circulation and affect metabolism, immune function, and even brain function through the gut-brain axis.
The more diverse your prebiotic intake, the more diverse the bacterial species that thrive — and microbiome diversity is consistently associated with better metabolic, immune, and mental health outcomes.
The best prebiotic foods
1. Jerusalem artichokes (sunchokes)
The highest inulin content of any common food (14–19g per 100g). Inulin specifically feeds Bifidobacterium, one of the most beneficial bacterial genera. Note: the high inulin concentration can cause significant gas in those unaccustomed. Start with very small amounts (30–50g) and build up.
2. Chicory root
Chicory is the richest source of inulin after Jerusalem artichoke, and inulin supplements are typically derived from chicory. Roasted chicory root is a common coffee substitute. Fresh chicory leaves have a lower concentration but are more palatable.
3. Garlic
One of the most prebiotic-dense foods gram for gram — high in fructooligosaccharides (FOS) and inulin. However, garlic is also one of the highest-FODMAP foods. If you have IBS, use garlic-infused oil (the FOS doesn’t transfer to oil, only the flavour compounds) as your source.
4. Onions
High in FOS. Same FODMAP caveat as garlic — the green tops of spring onions are low-FODMAP and still provide some prebiotic benefit.
5. Leeks
Rich in FOS and inulin. The green tops are lower in FODMAPs than the white bulb. A good mid-FODMAP prebiotic option.
6. Asparagus
Contains inulin, vitamin K, folate, and chromium. Low-FODMAP at 4–5 spears per serving. One of the gentler ways to increase prebiotic intake if you have IBS.
7. Oats
Beta-glucan in oats is the best-studied prebiotic after inulin/FOS. It specifically feeds Lactobacillus and Bifidobacterium, slows glucose absorption, and has the most robust evidence of any dietary fibre for cardiovascular benefits. Low-FODMAP at around 50g (dry) per serving.
8. Bananas (unripe)
A ripe banana is mostly simple sugars. An underripe (slightly green) banana contains significant resistant starch — which is fermented more slowly than inulin, producing butyrate over a longer timeframe. Low-FODMAP. One of the most gut-friendly prebiotic foods for people with IBS.
9. Cooked and cooled potatoes, rice, and pasta
When starchy foods are cooked and then cooled (in the fridge for at least 12 hours), some starch crystallises into a form resistant to amylase digestion. This retrograde resistant starch reaches the colon intact and feeds butyrate-producing bacteria. Reheating partially reduces the effect, so cold potato salad and rice salads maximise resistant starch content.
10. Legumes (beans, lentils, chickpeas)
Galactooligosaccharides (GOS) in legumes are highly prebiotic. They specifically support Bifidobacterium and Lactobacillus. The main limitation for people with IBS: legumes are high-FODMAP at large servings. Canned legumes, thoroughly rinsed, are lower in GOS and better tolerated in small portions (¼ cup).
11. Flaxseeds (ground)
Rich in soluble fibre and lignans (which beneficial bacteria convert into bioactive compounds). Ground flaxseed is more bioavailable than whole seeds. Low-FODMAP. Easy to add to yoghurt, smoothies, or porridge.
12. Blueberries and other dark berries
The polyphenols in blueberries (and raspberries, blackberries, and strawberries) aren’t technically fibre, but they function as prebiotics — feeding Bifidobacterium and Lactobacillus while inhibiting harmful bacteria. Low-FODMAP at typical serving sizes.
How to increase prebiotic intake without side effects
The main problem with suddenly increasing prebiotic foods is gas and bloating — because you’re dramatically increasing the fermentation substrate available to colonic bacteria. This is not harmful, but it’s uncomfortable.
The rule: increase total prebiotic fibre by no more than 3–5g per week. A tablespoon of ground flaxseed is ~2g. A 40g portion of rolled oats adds ~2g of beta-glucan. A medium banana (slightly unripe) adds ~3–5g of resistant starch.
A practical 4-week build-up:
Week 1: Add 1 tbsp ground flaxseed to breakfast daily.
Week 2: Swap one meal to include oats or cooled rice (resistant starch).
Week 3: Add 50g blueberries to one meal daily.
Week 4: Introduce one serving of asparagus or leek 3× per week.
By week 4, you’ve meaningfully increased prebiotic diversity without a dramatic fermentation overload. Continue expanding from here at your own pace.
Quick prebiotic-rich meal ideas
Overnight oats (cold): 50g rolled oats + 200ml kefir + 1 slightly unripe banana + 1 tbsp flaxseed — refrigerate overnight. Maximises resistant starch (cold oats), inulin (banana), beta-glucan (oats), and probiotics (kefir) in one bowl.
Cold potato salad: cooked, cooled baby potatoes + spring onion greens + capers + Dijon mustard + olive oil. The cooling step is what makes this high in resistant starch.
Asparagus and egg plate: grilled asparagus + 2 poached eggs + sourdough spelt + olive oil. Simple, low-FODMAP, genuinely prebiotic.
Blueberry flaxseed yoghurt: 150g live yoghurt + 80g blueberries + 1 tbsp ground flaxseed + 20g walnuts. A microbiome meal in a bowl.
Feeding your gut bacteria well is one of the highest-leverage dietary interventions available. The diversity and vibrancy of your microbiome depends, more than anything else, on the diversity of plant foods — especially prebiotic fibres — that you consistently eat.
Frequently asked questions
What's the difference between prebiotics and probiotics?
Probiotics are live beneficial bacteria introduced into your gut (via fermented foods or supplements). Prebiotics are the non-digestible compounds — primarily certain types of fibre — that feed and sustain the bacteria already living in your gut. You need both, but prebiotics arguably matter more for long-term microbiome health: without an adequate supply of prebiotic fibre, any bacteria introduced by probiotics won't persist.
Can I eat prebiotic foods if I have IBS?
Many high-prebiotic foods are also high-FODMAP (onion, garlic, legumes, wheat). FODMAPs cause symptoms in IBS partly because they're prebiotic — the fermentation that feeds good bacteria also produces gas. If you have IBS, you can still eat prebiotics, but through low-FODMAP sources: unripe bananas, cooked and cooled potatoes/rice (resistant starch), oats, flaxseed, carrots, and blueberries. Introduce these slowly and build up.
How much prebiotic fibre do I need each day?
Research suggests 5–20g of prebiotic fibre per day supports microbiome health and diversity. The average person in the UK eats 16–18g of total fibre daily but much less specifically prebiotic fibre. Small, consistent increases — adding a banana, a tablespoon of flaxseed, or a portion of legumes daily — make a meaningful difference without overwhelming the gut.
Does cooking destroy prebiotics?
Some cooking reduces prebiotic content, but others are enhanced by it. Cooking and then cooling starchy foods (potatoes, rice, pasta) actually increases resistant starch content as the starch retrogrades. Inulin in asparagus and chicory is relatively heat-stable. The most significant losses occur in high-heat, long cooking — roasting or brief cooking better preserves prebiotic compounds than boiling.