How Much Fibre Do You Need a Day? The UK Answer by Age

Adults in the UK need 30 g of fibre a day, a figure set by the Scientific Advisory Committee on Nutrition (SACN) in 2015 and used by the NHS; children need about 15 g from age 2, 20 g from 5 and 25 g from 11. Most people are well short: the 2019 to 2023 National Diet and Nutrition Survey found adults averaging 16.4 g a day (men 17.3 g, women 15.5 g), and only 4% reached 30 g, including just 2% of women aged 19 to 64.^{1, 2} The 2016 to 2019 survey put adults at 19.7 g, the source of the NHS's "about 20 g"; the method changed in between, so the two figures sit side by side rather than as a trend.^{3, 4} The gap of about 14 g closes fastest with pulses, wholegrains, vegetables and fruit added over two to three weeks with more fluid, because a sudden jump brings wind before benefit.

How much fibre do you need by age and sex?

SACN scaled the children's figures from the adult 30 g by energy need, rounded to 5 g; the NHS uses the same bands.^{1, 4} Averages are from the 2019 to 2023 survey.²

Women of every age eat less fibre than men, and intake rises with income.² There is no separate figure for pregnancy or older age. On spelling, the British word is fibre; the American spelling ends in -er, and the nutrient is the same.

Where does the 30 g figure come from, and why did it rise?

SACN chose 30 g because, in the prospective studies it reviewed, intakes of 30 g and above were most consistently associated with lower rates of cardiovascular disease, type 2 diabetes and colorectal cancer, with the confidence intervals widening beyond that.¹ The previous figure of 18 g measured non-starch polysaccharide; SACN moved to the AOAC method, which counts more of what is in food, including resistant starch, so part of the rise is a change of ruler, not of advice.¹ The 2019 Lancet review of 185 prospective studies and 58 trials then found 15 to 30% lower all-cause and cardiovascular mortality, coronary disease, stroke, type 2 diabetes and colorectal cancer in the highest fibre consumers, greatest at 25 to 29 g a day, with the curves suggesting more benefit above that.⁷ These numbers describe fibre-rich diets in populations, not any supplement.

Gel, bulk or ferment: what are the three jobs a fibre does?

Most pages sort fibre into soluble and insoluble, but inulin and psyllium are both soluble and behave nothing alike. What predicts a fibre's effect is whether it forms a viscous gel in the small bowel, and whether it survives fermentation in the large bowel while holding water.⁵ Gel-formers slow glucose and bile-acid absorption, which is where the cholesterol and post-meal glucose effects come from; psyllium, a gel that resists fermentation, reaches the stool intact and softens hard stools while firming loose ones. Coarse wheat bran adds mass and speeds transit. Fully fermented fibres such as inulin feed bifidobacteria and make gas, and are weak laxatives, with one counterweight: short-chain fructans raised stool frequency by about 0.36 a day across 47 publications, which is why the register sets chicory inulin's claim at 12 g.^{5, 6}

What does fibre do? The outcomes, in numbers

Bowel habit. In 16 trials of 1,251 adults with chronic constipation, 66% responded to a fibre supplement against 41% on control; the benefit was clear only above 10 g a day and after four weeks or more, and psyllium was the best supported.⁸ Cholesterol. Three grams or more of oat beta-glucan a day lowered LDL by about 0.25 mmol/L across 28 trials, and psyllium at about 10 g a day by 0.33 mmol/L across another 28.^{9, 10} Blood sugar. Viscous fibre at about 13 g a day lowered HbA1c by 0.58 percentage points in people with type 2 diabetes on usual care; psyllium's effect scales with how far glucose has drifted and is absent at normal glucose.¹¹ Weight. Viscous fibre inside a calorie-restricted diet reduced body weight by a further 0.81 kg in 15 trials; psyllium before meals at about 11 g a day for five months reduced it by about 2.1 kg across six small trials, a pooling authored by employees of a psyllium manufacturer, and by 0.28 kg, not significantly, across all 22 psyllium trials.^{12, 13, 14}

What is a food allowed to say about fibre in Great Britain?

The GB register authorises wording for specific fibres at specific doses, and the conditions double as a dose guide.¹⁵ "Beta-glucans contribute to the maintenance of normal blood cholesterol levels" needs 3 g a day. "Chicory inulin contributes to normal bowel function by increasing stool frequency" needs 12 g a day, the dose that raised weekly stools from three to four in 44 constipated adults.¹⁶ "Wheat bran fibre contributes to an acceleration of intestinal transit" needs 10 g a day. "Dried plums/prunes contribute to normal bowel function" needs 100 g of dried plums a day; prune juice has no claim. Psyllium has no authorised GB claim at any dose; its evidence is the trial record above. Every generic "fibre" claim has been rejected, and "high fibre" on a label means 6 g or more per 100 g or 3 g per 100 kcal.^{4, 15}

What does 30 g of fibre look like in a UK day?

The NHS's own example day gets there without a supplement: wholemeal toast with peanut butter and an orange (about 8.3 g), wholemeal spaghetti with a lentil and tomato sauce (about 11 g), and grilled chicken with a skin-on baked potato, carrots and green beans (about 11.2 g), which is 30.5 g before any snack.⁴ The 864-post Mumsnet question, how on earth you reach 30 g on 1,200 to 1,500 calories, has the same answer with the bread and pasta taken out: pulses, vegetables and berries carry the most fibre for the fewest calories, and a kidney-bean chilli alone gives about 9 g per 120 g of beans.²¹ Tracking apps disagree because their databases use different methods; the UK reference is McCance and Widdowson's dataset, CoFID.²¹ And "30 plants a week" is a variety target that says nothing about grams. Which foods are high in fibre has the full UK table per portion and a January day built meal by meal.

What are the signs you are short of fibre, and the signs you have too much?

Too little shows first in the bowel: fewer than three bowel movements a week, hard, dry or lumpy stools, straining, and the feeling of not having finished, which is how the NHS describes constipation.²⁰ The organs that pay over years are the bowel and the heart, and there is no blood test for fibre. Too much, or too much too soon, shows as wind, bloating and cramps, and either loose stools or, when fluid is short, harder ones: in the fibre trials flatulence rose (standardised effect 0.80); up to 10 g of inulin a day was well tolerated, 10 g of oligofructose in one sitting was not.^{8, 17} The practical rule, practice rather than trial evidence, is to add about 5 g a week, spread across meals, with more fluid.

When is more fibre not the answer?

Fibre helps most people, most reliably as gel-forming psyllium above 10 g a day with fluid for a month; some readers eat plenty and are still constipated, and another spoonful makes them worse. In a small uncontrolled Singapore series, 63 clinic patients who cut fibre out went from one motion every 3.75 days to one a day; it cannot overturn the randomised trials, but it names the subgroup: slow transit, or a pelvic-floor problem with emptying, in whom added bulk raises straining without moving anything.¹⁸ Fibre also fails when an impaction has to clear first under a GP, with constipating medicines (iron tablets, opioid painkillers, some antidepressants, aluminium antacids), on a very low-volume diet, in perimenopause, and after a jump from under 10 g to 30 g in a week. The 2025 British Dietetic Association guideline is the UK reference.¹⁹ Our constipation guide sets out the NHS steps; why you are still constipated on lots of fibre covers the other reasons. See a GP for a sudden change in bowel habit, blood in the stool or unexplained weight loss, and never add bulk fibre while vomiting, in pain or backed up for days.²⁰

What is fibremaxxing, and is more than 30 g better?

Fibremaxxing is a social-media word from 2025 for deliberately pushing fibre past 30 g, often to 40 to 70 g. For the 96% of UK adults below 30 g it describes the right direction; the evidence runs out at about 30 to 35 g, where the cohort curves flatten, no trial has tested 50 g or more, and the SACN confidence intervals widen above 30 g.^{1, 7} Jumping from 15 to 50 g in a week brings weeks of wind, harder stools if fluid does not rise with it, and flares in IBS or inflammatory bowel disease; over two to four weeks with fluid, to 30 g, it is simply eating well.

Do supplements count towards 30 g, and where do they fit?

They count by their grams; food should carry most of the day, because the evidence is about fibre-rich diets, and a supplement's grams decide what it can do. A three-gummy serving of a typical inulin fibre gummy gives about 4 g of soluble fibre, about an eighth of the 30 g target and a third of the 12 g a day at which the register says chicory inulin contributes to normal bowel function by increasing stool frequency; what a gummy is for is a daily top-up of a few grams.^{15, 16, 17} A psyllium sachet typically gives 3.5 g of psyllium husk against the 10 to 12 g a day the trials used.⁸ Every bulk fibre comes with the same rules: never dry; at least 150 ml of fluid per 3.5 g, drunk before it thickens; not before sleep; an hour either side of other medicines, and tell your pharmacist what you take; and not at all with difficulty swallowing or a narrowing of the gut, because obstructions have followed dry powder and too little fluid.²²

How much fibre do you need on Mounjaro or another GLP-1 medicine?

The target does not change on tirzepatide or semaglutide, but a smaller plate has to carry more fibre per mouthful and the increase has to be slower. How much fibre you need on Mounjaro has the plan; why Mounjaro causes constipation and diarrhoea covers the bowel side; do GLP-1 supplements work puts the fibre numbers beside the medicines'.

Every guide in this series

This page is the hub. Live now: which foods are high in fibre and the constipation guide. Psyllium: what psyllium husk does, how to take psyllium husk, is psyllium husk safe and psyllium against chia and flaxseed. Prunes: does prune juice help constipation and is prune juice good for you. Also live: what is inulin, do fibre gummies work, why fibre makes you bloated and how much fibre children need. The supplement, weight, cholesterol, blood sugar, glucomannan, resistant starch and IBS pages are linked from here as each goes live.

What we don't know

Whether there is an upper limit, since the UK has set none and the cohort data thin out above about 35 g; the right figure for someone eating 1,300 kcal a day; and whether the bifidobacteria that fermentable fibres raise translate into anything a person can measure, which no human trial has shown.^{5, 7}

Frequently asked questions

Is one banana a day enough fibre?

No. An 80 g portion of banana gives about 1.1 g of fibre, roughly a twentieth of the day; pulses, wholegrains, berries, pears and dried fruit move the total.²¹

How do I get 30 g of fibre a day?

Two or three 5 g additions on top of what you already eat: a tin of beans or lentils in something you were cooking anyway (about 8 g per 120 g), wholegrain bread and pasta in place of white, 80 g of berries or a pear, and a handful of nuts or seeds.²¹ Add one a week, with a glass more water a day.

Does fibre help blood sugar?

The NHS says eating plenty of fibre is associated with a lower risk of type 2 diabetes.⁴ In people who already have it, viscous fibre at about 13 g a day lowered HbA1c by 0.58 percentage points in 28 trials; the register allows a post-meal glucose claim only for named fibres at set doses.^{11, 15}

Do fibre supplements count towards the 30 g?

Yes, by their grams: a serving that gives 4 g of inulin counts 4 g, and a sachet that gives 3.5 g of psyllium counts 3.5 g. The target was built on food, so a supplement is the top-up when a day falls short.

Sources

1. Scientific Advisory Committee on Nutrition. Carbohydrates and Health, 2015. gov.uk.
2. National Diet and Nutrition Survey 2019 to 2023. gov.uk.
3. National Diet and Nutrition Survey: results from years 9 to 11 (2016 to 2019). gov.uk.
4. NHS. How to get more fibre into your diet. nhs.uk.
5. McRorie JW, McKeown NM. Understanding the physics of functional fibers in the gastrointestinal tract. Journal of the Academy of Nutrition and Dietetics, 2017. PubMed 27863994.
6. de Vries J, et al. Effects of β-fructans fiber on bowel function: a systematic review and meta-analysis. Nutrients, 2019. PubMed 30621208.
7. Reynolds A, et al. Carbohydrate quality and human health. Lancet, 2019. PubMed 30638909.
8. van der Schoot A, et al. The effect of fiber supplementation on chronic constipation in adults. American Journal of Clinical Nutrition, 2022. PubMed 35816465.
9. Whitehead A, et al. Cholesterol-lowering effects of oat β-glucan: a meta-analysis of randomized controlled trials. American Journal of Clinical Nutrition, 2014. PubMed 25411276.
10. Jovanovski E, et al. Effect of psyllium (Plantago ovata) fiber on LDL cholesterol and alternative lipid targets. American Journal of Clinical Nutrition, 2018. PubMed 30239559.
11. Jovanovski E, et al. Should viscous fiber supplements be considered in diabetes control? Diabetes Care, 2019. PubMed 30617143.
12. Jovanovski E, et al. Effect of viscous fiber supplementation on obesity indicators in individuals consuming calorie-restricted diets. European Journal of Nutrition, 2021. PubMed 32198674.
13. Gibb RD, et al. Psyllium is a natural nonfermented gel-forming fiber that is effective for weight loss. Journal of the American Association of Nurse Practitioners, 2023. PubMed 37163454.
14. Darooghegi Mofrad M, et al. The effects of psyllium supplementation on body weight in adults. Critical Reviews in Food Science and Nutrition, 2020. PubMed 30880409.
15. Department of Health and Social Care. Great Britain nutrition and health claims (NHC) register. gov.uk.
16. Micka A, et al. Effect of consumption of chicory inulin on bowel function in healthy subjects with constipation. International Journal of Food Sciences and Nutrition, 2017. PubMed 27492975.
17. Bonnema AL, et al. Gastrointestinal tolerance of chicory inulin products. Journal of the American Dietetic Association, 2010. PubMed 20497775.
18. Ho KS, et al. Stopping or reducing dietary fiber intake reduces constipation and its associated symptoms. World Journal of Gastroenterology, 2012. PubMed 22969234.
19. Dimidi E, et al. British Dietetic Association guidelines for the dietary management of chronic constipation in adults. Journal of Human Nutrition and Dietetics, 2025. PubMed 41081513.
20. NHS. Constipation. nhs.uk.
21. Public Health England. McCance and Widdowson's Composition of Foods Integrated Dataset (CoFID), 2021. gov.uk. Portion values are approximate, from the British Nutrition Foundation and British Dietetic Association fibre fact sheets.
22. Shin S, et al. Acute esophageal obstruction after ingestion of psyllium seed husk powder: a case report. World Journal of Clinical Cases, 2022. PubMed 35321163.

This article is general information, not medical advice. See a GP about a sudden change in bowel habit, blood in the stool or unexplained weight loss, and ask a pharmacist before adding a fibre supplement if you take regular medicines, have difficulty swallowing or are pregnant or breastfeeding.