Sources

Last updated: October 4, 2026

Formulas & recommendations

• Institute of Medicine (2005). Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. National Academies Press. The Adequate Intake values and the 14 g per 1,000 kcal basis.
• U.S. Dietary Guidelines for Americans 2020-2025, which adopt the IOM values.
• FDA Daily Value for dietary fiber (28 g), used on Nutrition Facts labels. Set in the Daily Reference Value table at 21 CFR 101.9(c)(9).
• 21 CFR 101.81, Health claims: soluble fiber from certain foods and risk of coronary heart disease. Sets the daily intake levels behind the claim: 7 g or more of soluble fiber from psyllium seed husk, 3 g or more of beta-glucan from whole oats or barley.
• National Cholesterol Education Program Expert Panel (2002). Third Report on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III), Final Report. Circulation 106(25):3143-3421. The therapeutic lifestyle change diet, which lists 10 to 25 g a day of viscous (soluble) fiber and 2 g a day of plant stanols and sterols as options for lowering LDL cholesterol alongside saturated fat below 7% of calories. The source of the 10 to 25 g figure on our soluble fiber calculator.
• Evert AB, Dennison M, Gardner CD, Garvey WT, Lau KHK, MacLeod J, Mitri J, Pereira RF, Rawlings K, Robinson S, Saslow L, Uelmen S, Urbanski PB, Yancy WS (2019). “Nutrition Therapy for Adults With Diabetes or Prediabetes: A Consensus Report.” Diabetes Care 42(5):731-754. The American Diabetes Association position behind our fiber for diabetes page: a floor of at least 14 g of fiber per 1,000 kcal with at least half of grain intake as whole intact grains, the A1C reduction of 0.2 to 0.3 percentage points reported at intakes above 50 g a day along with the flatulence, bloating and diarrhea that accompany them, the preference for meeting intake through naturally high-fiber foods rather than supplements, and the finding from two systematic reviews that glycemic index and glycemic load had no significant effect on A1C.
• NGSP, the National Glycohemoglobin Standardization Program master equation relating IFCC units to DCCT/NGSP units (NGSP% = 0.09148 x IFCC mmol/mol + 2.152). The basis for converting a difference of 2.00 mmol/mol in HbA1c into about 0.18 percentage points.

Label rules

• 21 CFR 101.54, Nutrient content claims for “good source,” “high,” “more.” A food may say high, rich in or excellent source of fiber at 20% or more of the Daily Value per reference amount (5.6 g), and good source, contains or provides at 10 to 19% (2.8 to 5.5 g). A fiber claim on a food that is not low in total fat must disclose the fat level next to it.
• 21 CFR 101.9(c)(6), Carbohydrate, total. Total carbohydrate on a US Nutrition Facts label is calculated by subtracting the sum of crude protein, total fat, moisture and ash from the total weight of the food, which means dietary fiber is already inside the total. There is no federal definition of “net carbohydrate”. The basis for the net carb method on our fiber for diabetes page.
• 21 CFR 101.9(c)(6)(i), the definition of dietary fiber. Covers fiber intrinsic and intact in plants plus seven named isolated or synthetic non-digestible carbohydrates: beta-glucan soluble fiber, psyllium husk, cellulose, guar gum, pectin, locust bean gum and hydroxypropylmethylcellulose.
• FDA (2018). The Declaration of Certain Isolated or Synthetic Non-Digestible Carbohydrates as Dietary Fiber on Nutrition and Supplement Facts Labels; Guidance for Industry. 83 FR 27793, June 15 2018. Names the eight FDA intends to add to that definition, among them inulin and inulin-type fructans, polydextrose, and mixed plant cell wall fibers such as sugar cane fiber.
• 21 CFR 101.4(a)(1). Ingredients are listed in descending order of predominance by weight, which is what lets an ingredient list rank the fiber sources in a packaged snack.
• 21 CFR 101.12, Table 2, Reference amounts customarily consumed per eating occasion. The breakfast cereal rows set the serving basis used on our high-fiber cereal ranking: 15 g for ready-to-eat cereals weighing under 20 g per cup, 40 g at 20 to 43 g per cup and for cereals carrying 28 g or more of fiber per 100 g, 60 g at 43 g or more per cup and for biscuit types, and 40 g of plain dry hot cereal. The same table sets the grain rows used on our high-fiber whole grains ranking: 140 g prepared or 45 g dry for plain grains such as rice and barley, 140 g prepared or 55 g dry for plain pasta, 50 g for breads and rolls, and 15 g for bran or wheat germ.

Fiber supplements

• U.S. National Institutes of Health, Office of Dietary Supplements. Dietary Supplement Label Database (dsld.od.nih.gov). Supplement Facts panels as filed by manufacturers; the source of every product figure in our supplement comparison.
• McRorie JW Jr, McKeown NM (2017). “Understanding the Physics of Functional Fibers in the Gastrointestinal Tract: An Evidence-Based Approach to Resolving Enduring Misconceptions about Insoluble and Soluble Fiber.” Journal of the Academy of Nutrition and Dietetics 117(2):251-264.
• van der Schoot A, Drysdale C, Whelan K, Dimidi E (2022). “The Effect of Fiber Supplementation on Chronic Constipation in Adults: An Updated Systematic Review and Meta-Analysis of Randomized Controlled Trials.” American Journal of Clinical Nutrition 116(4):953-969.
• 21 CFR 201.319, Water-soluble gums, hydrophilic gums, and hydrophilic mucilloids (including, but not limited to, agar, alginic acid, calcium polycarbophil, carboxymethyl- cellulose sodium, chondrus, glucomannan, guar gum, karaya gum, methylcellulose, plantago seed, polycarbophil, psyllium, and tragacanth) as active ingredients; required warnings and directions. The source of the direction to take each dry-form dose with at least 8 ounces of liquid, and of the choking warning.

Constipation trials

• Yang J, Wang HP, Zhou L, Xu CF (2012). “Effect of dietary fiber on constipation: A meta analysis.” World Journal of Gastroenterology 18(48):7378-7383. Five randomized trials of dietary fiber; the source of the finding that stool frequency improved while consistency, treatment success, laxative use and painful defecation did not.
• Chey SW, Chey WD, Jackson K, Eswaran S (2021). “Exploratory Comparative Effectiveness Trial of Green Kiwifruit, Psyllium, or Prunes in US Patients With Chronic Constipation.” American Journal of Gastroenterology 116(6):1304-1312. The four-week head-to-head trial behind the 2 kiwifruit, 100 g prunes and 12 g psyllium daily doses.
• Attaluri A, Donahoe R, Valestin J, Brown K, Rao SS (2011). “Randomised clinical trial: dried plums (prunes) vs. psyllium for constipation.” Alimentary Pharmacology and Therapeutics 33(7):822-828. The eight-week crossover trial that matched both arms at 6 g of fiber a day.
• Rao SSC, Brenner DM (2021). “Efficacy and Safety of Over-the-Counter Therapies for Chronic Constipation: An Updated Systematic Review.” American Journal of Gastroenterology 116(6):1156-1181. The source of the treatment grades; its funding statement names Bayer US LLC, which sells a polyethylene glycol product.
• Ho KS, Tan CYM, Mohd Daud MA, Seow-Choen F (2012). “Stopping or reducing dietary fiber intake reduces constipation and its associated symptoms.” World Journal of Gastroenterology 18(33):4593-4596. The 63-patient single-arm cohort behind the reducing-fiber figures on our page asking whether fiber makes you poop. It had no control group and no blinding, and every patient was already on a high-fiber diet or supplements at entry.
• Voderholzer WA, Schatke W, Mühldorfer BE, Klauser AG, Birkner B, Müller-Lissner SA (1997). “Clinical response to dietary fiber treatment of chronic constipation.” American Journal of Gastroenterology 92(1):95-98. One hundred and forty-nine patients with chronic constipation at two Munich gastroenterology departments, treated with Plantago ovata seeds at 15 to 30 g a day for at least six weeks, then classified by colon transit measurement and rectoanal testing. The source of every responder figure on our page asking whether too much fiber can cause constipation: no effect in 84 patients, improved in 33, symptom free in 32, with 80% of slow-transit patients and 63% of patients with a disorder of defecation not responding against 85% of patients with no pathological finding who improved or became symptom free. It had no placebo arm.
• Anti M, Pignataro G, Armuzzi A, Valenti A, Iascone E, Marmo R, Lamazza A, Pretaroli AR, Pace V, Leo P, Castelli A, Gasbarrini G (1998). “Water supplementation enhances the effect of high-fiber diet on stool frequency and laxative consumption in adult patients with functional constipation.” Hepatogastroenterology 45(21):727-732. One hundred and seventeen patients randomized to the same diet of about 25 g of fiber a day for two months with either ad libitum fluid, which averaged 1.1 litres a day, or an instruction to drink 2 litres, which averaged 2.1. The source of the fluid figures on that page. Both arms improved on stool frequency and laxative use, and the higher-fluid arm improved significantly more on both.
• Chung BD, Parekh U, Sellin JH (1999). “Effect of increased fluid intake on stool output in normal healthy volunteers.” Journal of Clinical Gastroenterology 28(1):29-32. Fifteen healthy volunteers given an extra 1 litre and then an extra 2 litres a day over baseline. The source of the finding that extra fluid alone did not significantly change stool output while urine output rose.
• Müller-Lissner SA, Kamm MA, Scarpignato C, Wald A (2005). “Myths and misconceptions about chronic constipation.” American Journal of Gastroenterology 100(1):232-242. The source of two statements we quote: that there is no evidence constipation can be treated by increasing fluid intake unless there is evidence of dehydration, and that many patients with more severe constipation get worse symptoms when increasing dietary fiber.
• Mertz H, Naliboff B, Mayer EA (1999). “Symptoms and physiology in severe chronic constipation.” American Journal of Gastroenterology 94(1):131-138. One hundred and eight constipated patients put through colon transit studies, anorectal manometry and rectal sensory testing alongside symptom questionnaires. The source of the finding that pelvic floor symptom scores and straining correlated with no electromyographic or manometric measure of defecatory function, and that patients with pelvic floor dysfunction and those with no abnormality found had no specific symptoms.
• White N (2020). “A Guide to Recommending Fiber Supplements for Self-Care.” American Journal of Lifestyle Medicine 14(6):589-591. Summarises the physiochemical framework of solubility, viscosity, gel formation and degree of fermentation, and states which fiber types produce laxation and which do not. The source of the fermentation split on that same page. It declares no funding and no conflicts of interest, and it also gives the 17 g a day average US adult fiber intake, citing Reicks et al. 2014 on NHANES 2009 to 2010.
• University Hospitals (2024). “Constipated? Why More Fiber Might Not Be the Answer,” quoting gastroenterologist Vu Nguyen. The source of the fermentable-fiber, irritable bowel syndrome and Crohn’s disease cautions quoted on our fiber for constipation page.

Hemorrhoid evidence

• Alonso-Coello P, Guyatt G, Heels-Ansdell D, Johanson JF, Lopez-Yarto M, Mills E, Zhou Q (2005). “Laxatives for the treatment of hemorrhoids.” Cochrane Database of Systematic Reviews 2005(4):CD004649. The seven randomized trials in 378 patients behind every figure on our fiber for hemorrhoids page, including the per-trial fiber types, doses and durations, and the outcome-by-outcome relative risks.
• Alonso-Coello P, Mills E, Heels-Ansdell D, Lopez-Yarto M, Zhou Q, Johanson JF, Guyatt G (2006). “Fiber for the treatment of hemorrhoids complications: a systematic review and meta-analysis.” American Journal of Gastroenterology 101(1):181-188. The journal publication of the same review, reporting overall symptoms at RR 0.53 (95% CI 0.38 to 0.73) where the Cochrane version reports RR 0.47 (95% CI 0.32 to 0.68).
• Jensen SL, Harling H, Tange G, Shokouh-Amiri MH, Nielsen OV (1988). “Maintenance bran therapy for prevention of symptoms after rubber band ligation of third-degree haemorrhoids.” Acta Chirurgica Scandinavica 154(5-6):395-398. The 18-month trial of 20 grams of unprocessed bran a day, read through the Cochrane review.
• Peery AF, Sandler RS, Galanko JA, Bresalier RS, Figueiredo JC, Ahnen DJ, Barry EL, Baron JA (2015). “Risk Factors for Hemorrhoids on Screening Colonoscopy.” PLOS ONE 10(9):e0139100. The 2,813-participant cross-sectional study behind the straining, constipation and fiber-subtype odds ratios. Adjusted for age and sex.
• Kalkdijk J, Broens P, Ten Broek R, van der Heijden J, Trzpis M, Pierie JP, Klarenbeek B (2022). “Functional constipation in patients with hemorrhoids: a systematic review and meta-analysis.” European Journal of Gastroenterology and Hepatology 34(8):813-822. The source of the constipation coprevalence odds ratio of 2.09.
• Johannsson HO, Graf W, Pahlman L (2005). “Bowel habits in hemorrhoid patients and normal subjects.” American Journal of Gastroenterology 100(2):401-406. The comparison of 100 patients with grade 3 to 4 hemorrhoids against two control groups.
• American Gastroenterological Association (2026). “AGA Clinical Practice Update on Diagnosis and Treatment of Hemorrhoids: Expert Review.” Clinical Gastroenterology and Hepatology 24(7):1773-1781. The current best practice advice statements, including the first-line fiber and straining recommendation and the note that hemorrhoids cause significant pain only when acutely thrombosed.
• Hawkins AT, Davis BR, Bhama AR, et al. (2024). “The American Society of Colon and Rectal Surgeons Clinical Practice Guidelines for the Management of Hemorrhoids.” Diseases of the Colon and Rectum 67(5):614-623.
• National Institute of Diabetes and Digestive and Kidney Diseases. “Eating, Diet, and Nutrition for Hemorrhoids.” Last reviewed October 2016. The federal patient page, and the source of the 14 grams per 1,000 calories figure quoted across this topic.

Irritable bowel syndrome evidence

• Bijkerk CJ, de Wit NJ, Muris JW, Whorwell PJ, Knottnerus JA, Hoes AW (2009). “Soluble or insoluble fibre in irritable bowel syndrome in primary care? Randomised placebo controlled trial.” BMJ 339:b3154. The trial behind almost every soluble-over-insoluble recommendation: 275 primary care patients on 10 g a day of psyllium, wheat bran or rice-flour placebo for 12 weeks. The source of every responder rate, relative risk, dropout count and intake figure on our fiber for IBS page, including the 57 against 35 percent result in month one, the loss of significance by month three, the 18 of 97 bran patients who stopped for intolerance, and the 26.9 grams a day the group was already eating at baseline.
• Vasant DH, Paine PA, Black CJ, Houghton LA, Everitt HA, Corsetti M, Agrawal A, Aziz I, Farmer AD, Eugenicos MP, Moss-Morris R, Yiannakou Y, Ford AC (2021). “British Society of Gastroenterology guidelines on the management of irritable bowel syndrome.” Gut 70(7):1214-1240. The source of the recommendation-strength and evidence-quality grading we print for every first-line and second-line IBS treatment, the 3 to 4 gram starting dose and 20 to 30 gram target for soluble fibre, the updated pooled fiber estimate (RR 0.87, 95% CI 0.80 to 0.94, across 15 trials in 946 patients), the low FODMAP diet estimates (RR 0.71, 0.61 to 0.83, falling to 0.82, 0.67 to 1.01 against standard dietary advice), the peppermint oil estimate (RR 0.58, 0.34 to 0.98) and the three-month review point in its treatment algorithm.
• National Institute for Health and Care Excellence (2008, updated 2017). “Irritable bowel syndrome in adults: diagnosis and management.” NICE clinical guideline CG61. The source of recommendation 1.2.1.5, that clinicians should review fibre intake “adjusting (usually reducing) it” while monitoring symptoms, and of the dietary advice specifics we list: limiting high-fibre foods, three portions of fresh fruit a day at about 80 grams, three cups of tea or coffee, avoiding sorbitol with diarrhoea, and oats plus up to one tablespoon of linseed a day for wind and bloating.
• El-Salhy M, Ystad SO, Mazzawi T, Gundersen D (2017). “Dietary fiber in irritable bowel syndrome (Review).” International Journal of Molecular Medicine 40(3):607-613. The source of the fermentation-speed classification we use to separate soluble fibers from one another, including why short-chain highly fermentable fibers produce gas faster than the gut can clear it while psyllium does not, the 20 to 35 grams a day typically advised in primary care, and the ramp rate of no more than 5 grams a day each week.
• Varney J, Muir J, edited by Eswaran S. “Fiber in Irritable Bowel Syndrome.” International Foundation for Gastrointestinal Disorders, publication 129. The patient guide from the Monash group, and our source for inulin, fructo-oligosaccharides and pectin being classed as readily fermentable fibers.

Diverticular disease evidence

• Peery AF, Barrett PR, Park D, Rogers AJ, Galanko JA, Martin CF, Sandler RS (2012). “A high-fiber diet does not protect against asymptomatic diverticulosis.” Gastroenterology 142(2):266-272. The colonoscopy-based study of 2,104 patients behind the prevalence ratios for diverticulosis, including the finding that high fiber intake and more frequent bowel movements were associated with a higher rather than a lower prevalence.
• Ma W, Nguyen LH, Song M, Jovani M, Liu PH, Cao Y, Tam I, Wu K, Giovannucci EL, Strate LL, Chan AT (2019). “Intake of dietary fiber, fruits, and vegetables and risk of diverticulitis.” American Journal of Gastroenterology 114(9):1531-1538. The Nurses’ Health Study analysis of 50,019 women and 4,343 incident cases, and the source of every fiber subtype and individual food hazard ratio on our fiber and diverticulitis page, along with the incidence rates of 387 and 376 per 100,000 person-years.
• Ma W, et al. (2025). “Lifestyle factors, genetic susceptibility and risk of incident diverticulitis: an integrated analysis of four prospective cohort studies and electronic health records-linked biobank.” Gut, published online November 2025. The pooled analysis of 179,564 participants and 10,299 cases behind the five-factor lifestyle table and the polygenic risk score figures.
• Strate LL, Liu YL, Syngal S, Aldoori WH, Giovannucci EL (2008). “Nut, corn, and popcorn consumption and the incidence of diverticular disease.” JAMA 300(8):907-914. The Health Professionals Follow-up Study analysis of 47,228 men that tested the avoid-list foods and found no increased risk.
• Peery AF, Shaukat A, Strate LL (2021). “AGA clinical practice update on medical management of colonic diverticulitis: expert review.” Gastroenterology 160(3):906-911. The 14 best practice advice statements, including the clear liquid diet advice and its stated goal of patient comfort, the recurrence prevention list, and the statement that approximately 50% of diverticulitis risk is attributable to genetic factors.
• National Institute of Diabetes and Digestive and Kidney Diseases. “Eating, Diet, and Nutrition for Diverticular Disease.” Last reviewed August 2021. The federal patient page and its fiber-rich food table.

Low-fiber and low-residue diets

• Vanhauwaert E, Matthys C, Verdonck L, De Preter V (2015). “Low-Residue and Low-Fiber Diets in Gastrointestinal Disease Management.” Advances in Nutrition 6(6):820-827. The narrative review behind every definitional figure on our low-fiber diet page: the proposed maximum of 10 grams of fiber a day, the removal of the low-residue diet from the Nutrition Care Manual after 2011 for lack of a definition of residue, the nine bowel preparation studies in its Table 3, the European Society of Gastrointestinal Endoscopy recommendation for the day preceding colonoscopy, the Wu correlation between dietary residue score and the Ottawa bowel preparation scale, the Woolner and Kirby irritable bowel syndrome trial, and the 20 to 30 gram return target after diverticular symptoms resolve.
• Ho KS, Tan CYM, Mohd Daud MA, Seow-Choen F (2012). “Stopping or reducing dietary fiber intake reduces constipation and its associated symptoms.” World Journal of Gastroenterology 18(33):4593-4596. The 63-patient study of idiopathic constipation behind the bowel frequency, bloating and straining figures on our low-fiber diet page. Uncontrolled, with groups at six months formed by patient choice.
• Memorial Sloan Kettering Cancer Center. “Low-Fiber Diet,” patient education. The source of the three ceilings we cite: under 10 grams a day, under 3 grams a meal, under 2 grams a serving.
• MedlinePlus Medical Encyclopedia. “Low-fiber diet,” patient instructions. The source of the 10 to 15 grams a day figure.
• Mayo Clinic. “Low-fiber diet do’s and don’ts.” The source of the one-day sample menu we priced against USDA records, and of the 1 to 2 grams per serving rule. Its own reference list cites the Academy of Nutrition and Dietetics Nutrition Care Manual entry for fiber-restricted nutrition therapy at 13 grams.
• National Cancer Institute. “Low-Fiber Foods.” The federal food list, which carries no gram figures.

Colonoscopy preparation trials

• Taveira F, Areia M, Elvas L, Alves S, Brito D, Saraiva S, Cadime AT (2019). “A 3-day low-fibre diet does not improve colonoscopy preparation results compared to a 1-day diet: A randomized, single-blind, controlled trial.” United European Gastroenterology Journal. Registered as NCT02955901. The 412-patient trial behind every duration figure on our colonoscopy prep page: the 91.7 percent against 94.7 percent adequate preparation rates, the Boston Bowel Preparation Scale scores, the difficulty and adherence ratings, and the odds ratios for an inadequate preparation, including split-dose non-adherence at 30. It also reports the guideline position of a one-day diet at moderate evidence, a second randomized trial reaching the same result, and the observational study finding only the day before the procedure carried a significant effect.
• Alvarez-Gonzalez MA, Pantaleon MA, Flores-Le Roux JA, Zaffalon D, Amoros J, Bessa X, Seoane A, Pedro-Botet J (2019). “Randomized Clinical Trial: A Normocaloric Low-Fiber Diet the Day Before Colonoscopy Is the Most Effective Approach to Bowel Preparation in Colorectal Cancer Screening Colonoscopy.” Diseases of the Colon and Rectum 62(4):491-497. Registered as NCT02401802. The 276-participant Barcelona screening trial behind the comparison with a clear-liquid day: 89.1 percent against 95.7 percent adequate preparation, the hunger and fluid-perception scores, the laxative completion figures, and the diet plan built to up to 2,000 calories a day with mean fiber under 10 grams.

Population and condition-wide evidence

• Reynolds A, Mann J, Cummings J, Winter N, Mete E, Te Morenga L (2019). “Carbohydrate quality and human health: a series of systematic reviews and meta-analyses.” The Lancet 393(10170):434-445. Just under 135 million person-years from 185 prospective studies and 58 trials. The source of the 15 to 30% lower rates of all-cause and cardiovascular mortality, coronary heart disease, stroke, type 2 diabetes and colorectal cancer in the highest fiber consumers, and of the finding that risk reduction was greatest between 25 and 29 g a day.
• Reynolds AN, Akerman AP, Mann J (2020). “Dietary fibre and whole grains in diabetes management: Systematic review and meta-analyses.” PLoS Medicine 17(3):e1003053. Two cohorts of 8,300 adults in 22 countries followed a mean of 8.8 years, and 42 trials in 1,789 adults with prediabetes, type 1 or type 2 diabetes. The source of the HbA1c, fasting plasma glucose, body weight and mortality figures on our fiber for conditions page, including the 14 fewer deaths per 1,000 at 35 g a day against the 19 g average intake. It is also the source of every effect size, confidence interval, GRADE grade and meta regression result on our fiber for diabetes page: the per-marker table, the blood pressure null, the split of the HbA1c result by whether trials controlled participants’ weight (-2.67 mmol/mol from 28 trials against +1.26 from 5), the finding that fiber type did not influence any glycemic or lipid outcome, the higher HDL in non-viscous fiber trials, and the trial-base limits (93% of trials ran 6 to 12 weeks, 2 were in type 1 diabetes, none in gestational diabetes, heterogeneity of 90% or more on every pooled trial outcome).
• Moayyedi P, Quigley EM, Lacy BE, Lembo AJ, Saito YA, Schiller LR, Soffer EE, Spiegel BM, Ford AC (2014). “The effect of fiber supplementation on irritable bowel syndrome: a systematic review and meta-analysis.” American Journal of Gastroenterology 109(9):1367-1374. Fourteen randomized trials in 906 patients. The source of the overall relative risk of 0.86 (95% CI 0.80 to 0.94, NNT 10), the soluble fiber figure of 0.83 (0.73 to 0.94, NNT 7) and the null result for bran at 0.90 (0.79 to 1.03).
• Brown L, Rosner B, Willett WW, Sacks FM (1999). “Cholesterol-lowering effects of dietary fiber: a meta-analysis.” American Journal of Clinical Nutrition 69(1):30-42. Sixty-seven controlled trials. The source of the LDL reduction of 0.057 mmol/L per gram of soluble fiber a day (95% CI 0.044 to 0.070), tested across intakes of 2 to 10 g a day, and of the worked example in which 3 g of soluble fiber from oats lowers total and LDL cholesterol by about 0.13 mmol/L.

Gut microbiota evidence

• So D, Whelan K, Rossi M, Morrison M, Holtmann G, Kelly JT, Shanahan ER, Staudacher HM, Campbell KL (2018). “Dietary fiber intervention on gut microbiota composition in healthy adults: a systematic review and meta-analysis.” American Journal of Clinical Nutrition 107(6):965-983. Sixty-four studies in 2,099 participants. The source of every effect size on our high-fiber foods for gut health page: Bifidobacterium at SMD 0.64 (95% CI 0.42 to 0.86), Lactobacillus at 0.22 (0.03 to 0.41), fecal butyrate at 0.24 (0.00 to 0.47), the null results for alpha diversity, for the other prespecified bacteria and for the other short-chain fatty acids, and the subgroup finding that fructans and galacto-oligosaccharides produced significantly greater abundance of both genera. Registered at PROSPERO as CRD42016053101.
• Fu J, Zheng Y, Gao Y, Xu W (2022). “Dietary Fiber Intake and Gut Microbiota in Human Health.” Microorganisms 10(12):2507. The narrative review whose Table 2 tabulates the eleven dose-ranging trials behind the threshold table on the same page, along with the trial-level results attributed there to Kolida 2007, Reimer 2020, Calame 2008, Deehan 2020, Bouhnik 1999 and 2006, Tandon 2019, Maki 2012, Francois 2012, Fastinger 2008, Lefranc-Millot 2012 and Burns 2018. Also the source of the account of why viscous soluble fibers resist fermentation while short chains and small particles ferment fastest, and of the finding that alpha diversity fell in several fiber trials in healthy people while beta diversity results are the consistent ones.
• van Loo J, Coussement P, de Leenheer L, Hoebregs H, Smits G (1995). “On the presence of inulin and oligofructose as natural ingredients in the western diet.” Critical Reviews in Food Science and Nutrition 35(6):525-552. The source of the statement that inulin and oligofructose are not measured by classic methods of dietary fiber analysis and are consequently often not mentioned in food tables, and of the estimated western intake of 1 to 10 grams per person per day.
• Moshfegh AJ, Friday JE, Goldman JP, Ahuja JK (1999). “Presence of inulin and oligofructose in the diets of Americans.” Journal of Nutrition 129(7 Suppl):1407S-1411S. The USDA analysis of two 24-hour recalls from more than 15,000 Americans in the 1994-1996 Continuing Survey of Food Intakes by Individuals. The source of the average intakes of 2.6 g of inulin and 2.5 g of oligofructose a day, the range from 1.3 g in young children to 3.5 g in teenage boys and adult men, and the finding that wheat supplied about 70% and onions about 25% of these components.

Intake surveys

• Quagliani D, Felt-Gunderson P (2017). “Closing America’s Fiber Intake Gap: Communication Strategies From a Food and Fiber Summit.” American Journal of Lifestyle Medicine 11(1):80-85. The source of the finding that about 5% of the population meets fiber recommendations.

Food composition data

• USDA FoodData Central (api.nal.usda.gov/fdc): total dietary fiber and household serving values (SR Legacy), as published in standard clinical fiber tables.
• USDA FoodData Central, SR Legacy records read in September 2026 for total carbohydrate, dietary fiber, energy and portion weight. The source of the fiber, net carbohydrate and calorie columns in the ranking on our fiber for diabetes page, where net carbohydrate is total carbohydrate minus dietary fiber and cooked entries are taken without added salt.
• USDA FoodData Central, SR Legacy records read in September 2026 for total carbohydrate, dietary fiber, energy and household portion weights. The source of the 44-row table and every day-total on our high-fiber low-carb foods ranking, where net carbohydrate is total carbohydrate minus dietary fiber, the carb cost column is net carbohydrate divided by fiber scaled to 10 grams, and cooked entries are taken without added salt. The contrast day on that page uses the cooked lentil, cooked oat, cooked whole-wheat pasta and raw apple with skin records from the same release.
• USDA FoodData Central, SR Legacy records read in September 2026 for total dietary fiber and household portion weights. The source of every per-serving gram figure in the food table on our high-fiber foods for gut health page, where each value is the record’s fiber per 100 g multiplied by the portion weight carried on the same record.
• USDA FoodData Central, SR Legacy records read in September 2026 for total dietary fiber and household portion weights. The source of the per-portion table and bar chart on our page on what fiber does, where each value is the record’s fiber per 100 g multiplied by the portion weight on the same record, and the bran and dry cereal rows use the reference amounts at 21 CFR 101.12, Table 2.
• Centers for Disease Control and Prevention, “Fiber: The Carb That Helps You Manage Diabetes”, last reviewed May 15 2024. Quoted on our fiber for diabetes page for the Dietary Guidelines range of 22 to 34 g a day and for the soluble and insoluble description that the pooled trial evidence does not support.
• USDA FoodData Central, SR Legacy records read in October 2026 for total dietary fiber, energy and household portion weights. The source of the 32-row table, every per-ounce figure and the day totals on our high-fiber nuts and seeds ranking, where each value is the record’s fiber per 100 g multiplied by a portion weight carried on the same record, and the in-shell and hulled pumpkin seed rows come from records 170188 and 170557 respectively.
• USDA FoodData Central, Foundation Foods, records published October 2022, April 2023 and read in October 2026. The newer analytical values for almonds, pecans, pistachios, walnuts, brazil nuts, hazelnuts, macadamias, pine nuts, cashews, sunflower kernels and pumpkin seed kernels compared against their SR Legacy counterparts on that same page. Foundation and SR Legacy records are separate analyses of separate samples, not repeat measurements of one sample.
• USDA FoodData Central, Branded Foods. Nutrition Facts values, serving weights, package weights and ingredient lists as filed by manufacturers. The source of every packaged product figure on our high-fiber snacks ranking and every cereal figure on our high-fiber cereal ranking, where the household measure on each record is also what the grams-per-level-cup column is derived from.

Published figures we compare against

• Mayo Clinic, Chart of high-fiber foods. Quoted on our high-fiber vegetables page where its Brussels sprouts figure (4.5 g per cooked cup) differs from the USDA records.
• Alberta Health Services, Nutrition Services (February 2025). Eat More Soluble Fibre (handout 404276-NFS). The 5 to 10 g a day adult soluble fibre target, the gel-forming versus prebiotic and fermentable classification, and the per-serving soluble figures for legumes, vegetables, fruits, grains and seeds compared on our page about soluble fiber in lentils.
• Henry Ford Health (May 2026). Dish Up Some Berries For Added Fiber, a dietitian blog post. The eight-berry list quoted on our high-fiber berries ranking, where each of its figures is traced back to the USDA record it reproduces and the fresh, frozen and dried records are separated out.
• Soluble and Insoluble Fiber Foods List, the undated one-page handout circulated by the North Ottawa Wellness Foundation. The high published soluble figure for lentils (2.8 g per half cup) on the same page, quoted there alongside its apple and wheat bran values, which disagree with our split table.
• University of Florida IFAS Extension, FSHN13-06/FS229, Beans, Peas, and Lentils: Health Benefits. The description of legume fiber as especially high in the insoluble fraction and highly fermentable in the colon.
• The published soluble and insoluble food lists scored on our soluble vs insoluble fiber comparison, all read in October 2026: Google’s AI Overview for that query, which sources its two lists to Mayo Clinic, Dietary fiber: Essential for a healthy diet; MedlinePlus Medical Encyclopedia, Soluble vs. insoluble fiber (article 002136); Healthline, Soluble vs. Insoluble Fiber: Which One is Best For You?, whose food table is sourced to a 2025 StatPearls chapter; and WebMD, Types of Fiber: Soluble and Insoluble Fiber. The “listed as” column on that page records which side of these lists each food sits on, and the six foods Healthline files under both headings are its apples, pears, broccoli, rye, chia seeds and legumes.

Food safety

• Centers for Disease Control and Prevention (April 6, 1984). “Poisoning from Elderberry Juice, California.” MMWR 33(13):173-4. The outbreak and the editorial note behind the cooking caution on our high-fiber berries ranking: elderberries may be safe to consume, particularly if cooked, and leaves and stems should not be crushed in when making juice.

Soluble and insoluble fiber analyses

• Anderson JW, Bridges SR (1988). “Dietary fiber content of selected foods.” American Journal of Clinical Nutrition 47(3).
• Marlett JA (1992). “Content and composition of dietary fiber in 117 frequently consumed foods.” Journal of the American Dietetic Association 92(2).
• Li BW, Andrews KW, Pehrsson PR (2002). “Individual sugars, soluble, and insoluble dietary fiber contents of 70 high consumption foods.” Journal of Food Composition and Analysis 15(4).