Fiber: Official Intake Amounts, Food Sources and Side Effects
Official daily fiber amounts from US, UK and WHO sources, which foods supply fiber, what large reviews found, and why adding fiber too fast can cause gas and bloating.
Content last updated . This page has not been medically reviewed.
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Dietary fiber is the part of plant foods that people do not fully digest. Official bodies give different daily amounts, and most adults eat less than they suggest. The US Dietary Guidelines for Americans 2020-2025 report that more than 90 percent of women and 97 percent of men do not meet recommended fiber intakes. [1] The NHS says most UK adults eat an average of about 20 g a day. [2]
A practical caution first. Increasing fiber too quickly can lead to gas, bloating and cramps. [3] The US National Institute of Diabetes and Digestive and Kidney Diseases advises adding fiber a little at a time and drinking enough liquids to help it work. [4] If you have a bowel condition or unexplained bowel changes, ask a clinician or dietitian before changing how you eat; special conditions are not described in detail in the sources we read.
Official amounts
| Body, country, year | Amount for adults | Children |
|---|---|---|
| US Dietary Guidelines for Americans, 2020-2025 | Goal of 14 g per 1,000 kcal, based on levels observed to reduce coronary heart disease risk [1] | Adequate intake of 19 g for ages 12 to 23 months [1] |
| NIDDK (US), reviewed 2018 | 22 to 34 g a day, depending on age and sex [4] | Not given on that page |
| NHS (UK), reviewed 2026 | 30 g a day, as set by government guidelines [2] | About 15 g (ages 2 to 5), 20 g (5 to 11), 25 g (11 to 16) [2] |
| WHO fact sheet, 2026 | At least 25 g a day of naturally occurring fiber for everyone older than 10 [5] | At least 15 g (ages 2 to 5) and 21 g (6 to 9) [5] |
These are population guidance values. A clinician or dietitian decides what is right for a person.
Types and food sources
MedlinePlus describes two types. Soluble fiber attracts water and turns to gel during digestion, and is found in oat bran, barley, nuts, seeds, beans, lentils, peas and some fruits and vegetables. Insoluble fiber adds bulk to stool and is found in wheat bran, vegetables and whole grains. [6] NIDDK lists these example sources: [4]| Group | Examples named by NIDDK |
|---|---|
| Whole grains | Whole wheat bread and pasta, oatmeal, bran flake cereals |
| Legumes | Lentils, black beans, kidney beans, soybeans, chickpeas |
| Fruits | Berries, apples with the skin on, oranges, pears |
| Vegetables | Carrots, broccoli, green peas, collard greens |
| Nuts | Almonds, peanuts, pecans |
The NHS says foods labeled "high-fibre" have 6 g or more of fiber per 100 g. [2] The Dietary Guidelines add that replacing processed meats with beans, peas and lentils would increase dietary fiber. [1] See also legumes, whole grains and fiber claims on packages.
What research shows
| Question | What the source found | Strength of evidence |
|---|---|---|
| Heart disease, diabetes, cancer and death | A 2019 Lancet series (185 prospective studies, 58 trials) found 15 to 30% lower rates for the highest fiber eaters in observational data, with the greatest risk reduction at 25 to 29 g a day. [7] | Promising but limited for causation; authors graded certainty as moderate |
| Weight, blood pressure, cholesterol | In the same series, trials showed lower body weight, systolic blood pressure and total cholesterol with higher fiber intake. [7] | Promising but limited |
| People with diabetes | A meta-analysis of 42 trials found higher fiber lowered HbA1c, fasting glucose and LDL cholesterol; all trial analyses had high heterogeneity. [8] | Mixed (heterogeneous) |
| Whole foods versus isolated fiber | A review notes population benefits come from unrefined whole foods, while trials often tested isolated fibers; dose and type questions remain open. [9] | Limits stated by authors |
| Constipation | A meta-analysis of 16 trials of fiber supplements found a response in 66% versus 41% on control, with psyllium and pectin effective, and more flatulence. [10] | Promising but limited (supplements) |
Fiber supplements are a different product from food: see psyllium and fiber supplements. For constipation, British Dietetic Association guidelines (2025) made food recommendations only for kiwifruit, prunes and rye bread, and none for whole-diet approaches because evidence was lacking. [11]
Side effects and who needs extra care
- Gas, bloating, cramps: a review of 103 trials of non-digestible carbohydrates found overconsumption can cause undesirable gastrointestinal effects. [12]
- Irritable bowel syndrome: fructans in some high-fiber foods count as FODMAPs, and a guideline endorses a limited low-FODMAP trial. [13] See prebiotic foods.
- Celiac disease: NIDDK warns a gluten-free diet started without advice may not provide enough fiber, iron and calcium. [14]
- Older adults: NIDDK says older adults sometimes eat too little fiber, partly from reduced interest in food. [4]
- Medicines: interactions between fiber foods and medicines are not described in the sources we read for this page. Ask a pharmacist.
Related pages
Foods for gut health and bloating and nutrients and compounds in foods.Frequently asked questions
How much fiber should I eat a day?
Official figures differ: 22 to 34 g (NIDDK), 30 g (NHS) and at least 25 g (WHO). [4] [2] [5]
Which foods are highest in fiber?
NIDDK names whole grains, legumes, fruits, vegetables and nuts; the NHS defines high-fibre foods as 6 g or more per 100 g. [4] [2]
Why does more fiber cause gas?
Going up too fast can cause gas, bloating and cramps. [3]
What is the difference between soluble and insoluble fiber?
Soluble fiber forms a gel; insoluble fiber adds bulk to stool. [6]
Do I need a fiber supplement?
The sources we read for this page name foods as the sources of fiber. [4] Supplements are a separate product, covered on psyllium and fiber supplements; a clinician or pharmacist can advise.
References
- US Department of Agriculture and US Department of Health and Human Services. Dietary Guidelines for Americans, 2020-2025. 9th edition. Read 2026-10-23.
- NHS. How to get more fibre into your diet. Page last reviewed 2 March 2026. Read 2026-10-23.
- MedlinePlus (US National Library of Medicine). Dietary Fiber. Read 2026-10-23.
- NIDDK (US National Institutes of Health). Eating, Diet, & Nutrition for Constipation. Last reviewed May 2018. Read 2026-10-23.
- World Health Organization. Healthy diet fact sheet. Dated 26 January 2026. Read 2026-10-23.
- MedlinePlus (US National Library of Medicine). Soluble vs. insoluble fiber. Review date 8/25/2026. Read 2026-10-23.
- Reynolds A et al. Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. Lancet (London, England) 2019. PMID 30638909. Read 2026-10-23.
- Reynolds AN et al. Dietary fibre and whole grains in diabetes management: Systematic review and meta-analyses. PLoS medicine 2020. PMID 32142510. Read 2026-10-23.
- Gill SK et al. Dietary fibre in gastrointestinal health and disease. Nature reviews. Gastroenterology & hepatology 2021. PMID 33208922. Read 2026-10-23.
- van der Schoot A et al. The Effect of Fiber Supplementation on Chronic Constipation in Adults: An Updated Systematic Review and Meta-Analysis of Randomized Controlled Trials. The American journal of clinical nutrition 2022. PMID 35816465. Read 2026-10-23.
- Dimidi E et al. British Dietetic Association Guidelines for the Dietary Management of Chronic Constipation in Adults. Journal of human nutrition and dietetics : the official journal of the British Dietetic Association 2025. PMID 41081513. Read 2026-10-23.
- Mysonhimer AR et al. Gastrointestinal Effects and Tolerance of Nondigestible Carbohydrate Consumption. Advances in nutrition (Bethesda, Md.) 2022. PMID 36041173. Read 2026-10-23.
- Lacy BE et al. ACG Clinical Guideline: Management of Irritable Bowel Syndrome. The American journal of gastroenterology 2021. PMID 33315591. Read 2026-10-23.
- NIDDK (US National Institutes of Health). Eating, Diet, & Nutrition for Celiac Disease. Last reviewed October 2020. Read 2026-10-23.