Prebiotics
Prebiotic fibres in powder and capsules: chicory inulin, FOS, GOS, acacia and partially hydrolysed guar gum. We explain which fibre suits a sensitive gut, which dose does something and how to build up slowly.Read more →
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Prebiotic fibre: which type, which dose, and how your gut reacts
Prebiotics are fibres your body cannot digest. They pass through the small intestine unchanged and reach the colon, where your gut bacteria ferment them. That fermentation is the whole point, and it is also why the first week can feel gassy. Not every fibre is a prebiotic. Psyllium mainly adds bulk and holds water, while inulin, FOS and GOS are actively eaten by bacteria such as bifidobacteria.
UK guidance puts adult fibre intake at 30 grams a day, and average intake sits far below that. A supplement is a top-up on food, not a swap for vegetables, pulses and wholegrains. Most people land here after reading about the bacteria living in the gut and wanting one measurable thing to add to breakfast.
The fibres differ more than the labels suggest
Almost every product on this page uses one of five fibre families:
- Chicory inulin: long chains, ferments slowly and deep in the colon.
- FOS (oligofructose): shorter chains from the same source, ferments faster, so gas shows up sooner.
- GOS (galacto-oligosaccharides): milk-sugar based chains, often used in small daily doses.
- Acacia fibre and partially hydrolysed guar gum: slow, mild fermenters, the usual pick for a sensitive gut.
- Resistant starch: from green banana or potato, works low in the colon.
Dose decides what you actually notice. Chicory inulin carries the one authorised European claim in this category: it contributes to normal bowel function by increasing stool frequency, at 12 grams a day. Plenty of capsule products deliver one or two grams, which is nowhere near that figure. Powders let you weigh your way up gram by gram. Note too that many supplements with live bacteria already carry a gram of FOS, so check the label before you stack two products.
How we choose the prebiotics we stock
We judge three things: the fibre itself, the grams per serving, and whether a combination adds anything. We prefer products that print the fibre name and the dose on the front, because "prebiotic blend" tells you nothing about what you are taking. Powders earn a place when you need to build up slowly, capsules when a small fixed dose is enough. We buy directly from the brands, every product passes our compliance team before it goes live, and we test products ourselves while independent labs spot-check batches. You can read how we select brands and products.
Who this suits, and who should go carefully
Prebiotic fibre fits people whose diet is short on plants, who travel often, or who want a fixed daily amount instead of guessing. Give it two to three weeks of consistent use before you judge it, and start at roughly a third of the serving on the tub. Inulin and FOS are fructans, a group many people with IBS are advised to limit, so acacia fibre or partially hydrolysed guar gum is usually the calmer starting point. If wind is your main complaint rather than regularity, a bulking fibre such as psyllium husk may suit you better than a fast-fermenting one. Drink enough water either way: fibre draws water into the bowel and works poorly without it.
Frequently asked questions
Prebiotics are fibres your own enzymes cannot break down. They reach the colon intact, where your gut bacteria ferment them. Probiotics are something else entirely: live bacteria that you swallow. The short version is that prebiotics are food and probiotics are the residents. That difference matters when you shop, because a prebiotic product is judged on the type of fibre and the grams per serving, while a live bacteria product is judged on strains and counts.
Food first. UK guidance sets a daily fibre target that most people do not reach, and vegetables, pulses, oats and fruit give you a wider mix of fibres than any single supplement. A prebiotic is useful as a top-up when your diet is narrow or your routine is unpredictable. Compare your usual day against the reference figures below before deciding.
| Age group | Fibre per day |
|---|---|
| Adults | 30 g |
| Secondary school age | 25 g |
| Primary school age | 20 g |
| From age two | 15 g |
Pick on tolerance first, then on convenience. Fast-fermenting fibres act higher in the gut and produce gas sooner, slow fermenters are gentler but less noticeable at first.
| Fibre | Source | Fermentation | Suits |
|---|---|---|---|
| Chicory inulin | Chicory root | Slow, long chain | Regularity, higher doses |
| FOS | Chicory, fruit | Fast | Small doses, sturdy gut |
| GOS | Lactose based | Moderate | Low daily amounts |
| Acacia fibre | Gum arabic | Slow, mild | Sensitive digestion |
| Guar gum (PHGG) | Guar bean | Slow, mild | Building up gradually |
Powder gives you control over grams, capsules give you a fixed small dose.
Start at roughly a third of the serving on the pack for the first week, then increase in small steps. For chicory inulin specifically, the authorised European claim on bowel function applies at 12 grams a day, which you can split across servings. That is more than most capsules provide, so read the label rather than the front of the tub. Building up slowly is not caution for its own sake: your gut bacteria adapt over days, not hours.
With a meal is the practical choice for most people. Fibre mixed into food tends to sit better than a concentrated dose on an empty stomach, and tying it to breakfast makes it easier to stay consistent. Timing is far less important than doing it every day. Drink a full glass of water with it, because fibre pulls water into the bowel and does its job poorly when you are short on fluid.
Gas is the by-product of fermentation, so some wind means the fibre is being used. It is most noticeable when you start too high or jump the dose quickly, and it usually settles once your gut bacteria adjust over a couple of weeks. If it does not settle, the fibre type is the thing to change, not just the amount. Acacia and partially hydrolysed guar gum ferment more slowly than inulin or FOS and are generally easier to live with.
Yes, and many products already combine them. Check the ingredient list first: live bacteria capsules often include a gram of FOS as a carrier, which counts towards your daily fibre and can explain unexpected wind. If you take them separately and notice bloating, try them at different meals. Both work on the same area, so browse our supplements for digestion if you want the full picture before combining.
Inulin and FOS are fructans, one of the fermentable carbohydrate groups a low FODMAP diet restricts, so they are often the wrong starting point during an elimination phase. Reactions are individual: some people manage a few grams, others react to less. If you are working with a dietitian, follow their plan rather than a product label. When you do want fibre, the slow, mildly fermenting options such as acacia fibre or partially hydrolysed guar gum are the ones usually tolerated best.
