Dietary fiber, found in all plant-based foods, plays an essential role in human health. Most whole foods contain a combination of the two types of fiber, soluble and insoluble. Both types of fiber help maintain the health of your digestive system and promote regular bowel movements.
Soluble fiber pulls in water to form a gel in the digestive tract. This slows digestion, so your stomach and intestine do not absorb as much of some nutrients, like starch and sugar. As a result, cholesterol levels go down over time, which may help prevent heart disease and stroke. Consuming soluble fiber may also improve glucose tolerance in people with diabetes. This type of fiber is a common ingredient in many over-the-counter laxatives. Psyllium husk (which contains both soluble and insoluble fiber), pectin, and the soft parts of fruits, dried beans, and peas are examples of soluble fiber.
Insoluble fiber, on the other hand, can be found in the peels of fruit, such as apples, blueberries, and grapes. It acts as a natural laxative that speeds the passage of foods through the stomach. It also gives stool its bulk and helps it move quickly through the gastrointestinal tract.
Studies suggest that getting more fiber in your diet may play a role in the treatment of conditions such as gastrointestinal disease, constipation, hemorrhoids, high cholesterol, heart disease, stroke, diabetes, and some forms of cancer. Most Americans do not get the recommended amount of fiber (25 to 35 g. per day) in their daily diet.
Many studies show that fiber relieves constipation. Researchers think fiber relieves constipation by adding bulk to stool and helping it move faster through the intestines. If you have impacted stool, which is a complication of constipation, DO NOT take fiber supplements without talking to your doctor first.
Fiber can be used to relieve mild-to-moderate diarrhea. Soluble fiber soaks up water in the digestive tract, which makes stool firmer and slower to pass.
Irritable bowel syndrome (IBS)
Several studies show that soluble fiber helps regulate stool frequency and consistency in people with IBS. Psyllium and bran are the best studied soluble fiber sources in the treatment of IBS.
Your doctor may recommend soluble fiber to help soften stool and reduce the pain associated with hemorrhoids.
Inflammatory bowel disease (IBD)
A clinical study of people with ulcerative colitis (a type of IBD) found that psyllium seeds were as effective as the prescription drug mesalamine (Rowasa) in reducing recurrences of the disease. Speak to your doctor about the right form and dosage of fiber.
People with diverticulosis often take fiber supplements to prevent constipation and stop the condition from progressing. The National Academy of Nutrition and Dietetics recommends 25 to 30 g. of fiber per day. Your doctor may recommend more. Some researchers think that people with diverticulosis should avoid foods such as nuts and pumpkin, caraway, and sesame seeds. They believe these small particles may get lodged in the diverticula (pouches in the colon) and cause infection and irritation.
Soluble fibers, such as those in psyllium husk (which contains both soluble and insoluble fiber), guar gum, flaxseed, and oat bran, can help lower cholesterol when added to a low saturated fat, low cholesterol diet. Clinical studies show that psyllium in particular is effective in lowering total cholesterol levels as well as LDL (bad) cholesterol levels.
Studies show that a high fiber diet may help prevent type 2 diabetes, lower insulin and blood sugar levels, and improve cholesterol and triglyceride (fats in the blood) levels in people with diabetes. In addition, one well-designed clinical study suggests that pregnant women with type 1 diabetes may be able to reduce the amount of insulin they use if they eat a high-fiber diet.
A clinical study compared people with type 2 diabetes, who were eating 50 g. of fiber daily, with people getting the recommended 24 g. of fiber daily. After 6 weeks, people on the higher-fiber diet had better control of blood glucose, insulin, and blood lipids. In another clinical study, a group of men with type 2 diabetes, who took psyllium twice daily, lowered blood glucose and lipid values compared to a control group taking a placebo.
Clinical studies and human case reports suggest that soluble fiber (such as psyllium, pectin, and guar gum) may make you feel more satisfied, so you eat less and lose weight. Research also suggests that high intakes of dietary fiber may help prevent weight gain in the waist circumference.
Eating more high-fiber foods (such as oatmeal, oat bran, psyllium, and legumes) may help lower heart disease risk.
There are conflicting results from studies examining whether a high-fiber diet can help prevent colon cancer. Some studies suggest fiber protects against the development of colorectal cancer. Most large, well-designed clinical studies, however, show only a small association between how much fiber people eat and their risk of colorectal cancer. In addition, fiber does not seem to protect against the recurrence of colorectal cancer in people who have already been treated for the condition.
Other types of cancer
Preliminary clinical evidence suggests that a diet high in fiber (in conjunction with lifestyle changes and conventional medication) may help protect against certain types of cancer such as prostate, breast, and uterine. More research is needed.
Preliminary evidence suggest that high dietary fiber intake is associated with reduced inflammation and a lower risk of death. These associations are more pronounced among people who have kidney disease.
Soluble fiber is found in dried beans and peas, oats, barley, legumes, fruits, flax, and psyllium seed husks.
Insoluble fiber is found primarily in fruits and vegetables, whole grain products, and wheat and corn bran.
Fiber is available as a supplement in several forms, including fiber tablets, capsules, and powders. Fiber is also available as bulk fiber laxatives, including psyllium.
How to Take It
The following are daily fiber recommendations from the National Academy of Sciences' Institute of Medicine:
For infants and children under 18 years of age, there is no daily fiber recommendation. Children with specific fiber needs should increase the amount of foods in their diets with fiber that they eat slowly over a period of days. DO NOT give fiber supplements to a child without first asking your doctor or pediatrician.
The National Academy of Nutrition and Dietetics recommends 20 to 35 g. per day from a variety of fiber-rich foods. If you are not getting enough fiber, you may need to add more fiber-rich foods to your diet. Choose whole grain products, raw or cooked fruits and vegetables, dried beans, and dried peas. Refined or processed foods, including fruit juices, white breads, pastas, rice, and non whole grain cereals, are lower in fiber. The grain refining process removes the outer coat (bran) from the grain, which lowers its fiber content. Peeling fruits and vegetables also decreases their fiber content.
Because supplements may have side effects, or interact with medications, you should take them only under the supervision of a knowledgeable health care provider.
In general, fiber supplements may reduce or delay your body's absorption of certain medications. Try to take medications at least 1 hour before or 2 to 4 hours after taking fiber.
You should always drink an 8 oz. glass of water with fiber supplements. It is also important to drink at least 6 to 8 full glasses of water throughout the day to avoid constipation. Taking fiber supplements without enough water may cause the supplement to swell and could cause choking. DO NOT take this product if you have difficulty swallowing. People with esophageal stricture (narrowing of the esophagus), or any other narrowing or obstruction of the gastrointestinal tract should not take fiber supplements.
If you have chest pain, vomiting, or difficulty swallowing or breathing after taking fiber supplements, seek immediate medical attention.
Fiber can cause gas and bloating.
If you have impacted stool, which is a complication of constipation, DO NOT take fiber supplements without first seeking the approval of your doctor.
It is rare, but people who take soluble fiber supplements for a long time may develop allergic reactions (even anaphylaxis).
If you are currently being treated with any of the following medications, you should not take fiber supplements without first talking to your doctor.
Antidepressant medications (tricyclic antidepressants): Dietary fiber may lower the blood levels and effectiveness of tricyclic antidepressant medications. If you take tricyclic medications, talk to your doctor before taking fiber supplements or adding more fiber to your diet. Tricyclic antidepressants include:
- Amitriptyline (Elavil)
- Doxepin (Sinequan)
- Imipramine (Tofranil)
Diabetes medications: Fiber supplements may help regulate blood sugar levels. But they can also reduce the absorption of some medications, such as glyburide (Diabeta) and metformin (Glucophage). Talk to your doctor before taking fiber supplements if you have diabetes. DO NOT take fiber supplements at the same time as your medications. Wait a few hours in between.
Carbamazepine: Taking soluble fiber such as psyllium with carbamazepine (Tegretol), a medication used to treat seizures, may decrease the absorption and effectiveness of carbamazepine. A doctor should monitor blood levels of anyone taking both soluble fiber and carbamazepine.
Cholesterol-lowering medications: Combining psyllium or other soluble fibers with cholesterol-lowering medications (known as bile acid sequestrants) may help lower cholesterol levels. If you take these medications, talk to your doctor to see whether psyllium is safe and right for you. These drugs include:
- Cholestyramine (Questran)
- Colestipol (Colestid)
One study found that when people taking simvastatin (Zocor) added psyllium supplements to their regimen, they lowered cholesterol levels as much as if they had been taking a double dose of simvastatin.
Digoxin: Fiber supplements may reduce the body's ability to absorb digoxin (Lanoxin), a medication used to regulate heart function. DO NOT take fiber supplements at the same time as digoxin.
Lithium: Clinical reports suggest that psyllium or other soluble fibers may lower lithium levels in the blood, making lithium less effective. Lithium levels should be monitored very closely by a doctor, especially if there is a big change in fiber intake.
Alberts DS, Martínez ME, Roe DJ, et al. Lack of effect of a high-fiber cereal supplement on the recurrence of colorectal adenomas. N Eng J Med. 2000;342(16):1156-1162.
Anderson JW, Allgood LD, Lawrence A, et al. Cholesterol-lowering effects of psyllium intake adjunctive to diet therapy in men and women with hypercholesterolemia: meta-analysis of 8 controlled trials. Am J Clin Nutr. 2000;71:472-479.
Anderson JW, Baird P, Davis RH, et al. Health benefits of dietary fiber. Nutr Rev. 2009;67(4):188-205.
Bazzano LA. Effects of soluble dietary fiber on low-density lipoprotein cholesterol and coronary heart disease risk. Curr Atheroscler Rep. 2008 Dec;10(6):473-7. Review.
Bazzano LA, He J, Ogden LG, Loria C, Vupputuri S, Myers L, Whelton PK. Legume consumption and risk of coronary heart disease in US men and women: NHANES epidemiologic follow-up study. Arch Intern Med. 2001;161(21):2573-2578.
Bonithon-Kopp C, Kronborg O, Giacosa A, Rath U, Faivre J. Calcium and fibre supplementation in prevention of colorectal adenoma recurrence: a randomised intervention trial. European Cancer Prevention Organisation Study Group. Lancet. 2000;356(9238):1286-1287.
Botterweck AA, van den Brandt PA, Goldbohm RA. Vitamins, carotenoids, dietary fiber, and the risk of gastric carcinoma: results from a prospective study after 6.3 years of follow up. Cancer. 2000;88(4):737-748.
Burke V, Hodgson JM, Beilin LJ, Giangiulioi N, Rogers P, Puddey IB. Dietary protein and soluble fiber reduce ambulatory blood pressure in treated hypertensives. Hypertension. 2001;38(4):821-826.
Chan MY. Sequential effects of a high-fiber diet with psyllium husks on the expression levels of hepatic genes and plasma lipids. Nutrition. 2008;24(1):57-66.
Chandalia M, Garg A, Lutjohann D, von Bergmann K, Grundy SM, Brinkley LJ. Beneficial effect of high dietary fiber intake in patients with type 2 diabetes mellitus. N Eng J Med. 2000;342:1392-1398.
Coleman HG, Murray LJ, Hicks B, et al. Dietary fiber and the risk of precancerous lesions and cancer of the esophagus: a systematic review and meta-analysis. Nutr Rev. 2013;71(7):474-82.
Dahm CC, Keogh RH, Spencer EA, et al. Dietary fiber and colorectal cancer risk: a nested case-control study using food diaries. J Natl Cancer Inst. 2010;102(9):614-26.
Dong J, He K, Wang P, Qin L. Dietary fiber intake and risk of breast cancer; a meta-analysis of prospective cohort studies. Am J Clin Nutr. 2011;94(3):900-5.
Du H, Van der A DL, Boshuizen HC, et al. Dietary fiber and subsequent changes in body weight and waist circumference in European men and women. Am J Clin Nutr. 2010;91(2):329-36.
Grooms KN, Ommerborn MJ, Pham DQ, Djousse L, Clark CR. Dietary fiber intake and cardiometabolic risks among US adults, NHANES 1999-2010. Am J Med. 2013;126(12):1059-67.e1-4.
Hermansen K, Sondergaard M, Hoie L, Carstensen M, Brock B. Beneficial effects of a soy-based dietary supplement on lipid levels and cardiovascular risk markers in type 2 diabetic subjects. Diabetes Care. 2001;24(2):228-233.
Howard BV, Manson JE, Stefanick ML, et al., Low-fat dietary pattern and weight change over 7 years: the Women's Health Initiative Dietary Modification Trial. JAMA. 2006;295(1):39-49.
Hu FB, Manson JE, Stampfer MJ, Colditz G, Liu S, Solomon CG, et al. Diet, lifestyle, and the risk of type 2 diabetes mellitus in women. N Engl J Med. 2001;345(11):790-797.
Karhunen LJ. A psyllium fiber-enriched meal strongly attenuates postprandial gastrointestinal peptide release in healthy young adults. J Nutr. 2010;140(4):734-44.
Jänne PA, Mayer RJ. Chemoprevention of colorectal cancer. N Engl J Med. 2000;342(26):1960-1968.
Jenkins DJ, Kendall CW, Vuksan V. Viscous fibers, health claims, and strategies to reduce cardiovascular disease risk. Am J Clin Nut. 2001;73(3):653-654.
Kalkwarf HJ, Bell RC, Khoury JC, Gouge AL, Miodovnik M. Dietary fiber intakes and insulin requirements in pregnant women with type 1 diabetes. J Am Diet Assoc. 2001;101(3):305-310.
Krauss RM, Eckel RH, Howard B, Appel LJ, Daniels SR, Deckelbaum RJ, et al. AHA Scientific Statement: AHA Dietary guidelines Revision 2000: A statement for healthcare professionals from the nutrition committee of the American Heart Association. Circulation. 2000;102(18):2284-2299.
Krishnamurthy V, Wei G, Baird B, et al. High dietary fiber intake is associated with decreased inflammation and all-cause mortality in patients with chronic kidney disease. Kidney Int. 2012;81(3):300-6.
Kurtz RC, Zhang ZF. Gastric cardia cancer and dietary fiber. Gastroenterology. 2001;120(2):568-70.
Liu S, Manson JE, Stampfer MJ, Hu FB, Giovannucci E, Colditz GA, et al. A prospective study of whole-grain intake and risk of type-2 diabetes mellitus in women. Am J Pub Health. 2000;90:1409-1415.
Lu LJ, Anderson KE, Grady JJ, Kohen F, Nagamani M. Decreased ovarian hormones during a soya diet: implications for breast cancer prevention. Can Res. 2000;60(15):4112-4121.
Ma Y, Hébert JR, Li W, Bertone-Johnson ER, Olendzki B, Pagoto SL, Tinker L, Rosal MC, Ockene IS, Ockene JK, Griffith JA, Liu S. Association between dietary fiber and markers of systemic inflammation in the Women's Health Initiative Observational Study. Nutrition. 2008 Oct;24(10):941-9.
MacDermott RP. Treatment of irritable bowel syndrome in outpatients with inflammatory bowel disease using a food and beverage intolerance, food and beverage avoidance diet. Inflamm Bowel Dis. 2007 Jan;13(1):91-6. Review.
Mayne ST, Risch HA, Dubrow R, Chow WH, Gammon MD, Vaughan TL, et al. Nutrient intake and risk of subtypes of esophageal and gastric cancer. Cancer Epidemiol Biomarkers Prev. 2001;10(10):1055-1062.
Mellen PB, Liese AD, Tooze JA, Vitolins MZ, Wagenknecht LE, Herrington DM. Whole-grain intake and carotid artery atherosclerosis in a multiethnic cohort: the Insulin Resistance Atherosclerosis Study. Am J Clin Nutr. 2007 Jun;85(6):1495-502.
Michels KB, Giovannucci E, Joshipura KJ, Rosner BA, Stampfer MJ, Fuchs CS, et al. Prospective study of fruit and vegetable consumption and incidence of colon and rectal cancers. J Natl Cancer Inst. 2000;92(21):1740-1752.
Moayyedi P, Quigley EM, Lacy BE, et al. The effect of fiber supplementation on irritable bowel syndrom: a systematic review and meta-analysis. Am J Gastroenterol. 2014;109(9):1367-74.
Mumford SL, Schisterman EF, Siega-Riz AM, et al. Effect of dietary fiber intake on lipoprotein cholesterol levels independent of estradiol in healthy premenopausal women. Am J Epidemiol. 2001;173(3):145-56.
National Cholesterol Education Program. Executive summary of the third report of the National Cholesterol Education Program (NCEP) expert panel on detection, evaluation, and treatment of high blood cholesterol in adults (Adult Treatment Panel III). JAMA. 2001;285(19):2486-2497.
Ning H, Van Horn L, Shay CM, Lloyd-Jones DM. Associations of dietary fiber intake with long-term predicted cardiovascular disease risk and C-reactive protein levels (from the National Health and Nutrition Examination Survey Data [2005-2010]). Am J Cardiol. 2014;113(2):287-91.
North CJ, Venter CS, Jerling JC. The effects of dietary fibre on C-reactive protein, an inflammation marker predicting cardiovascular disease. Eur J Clin Nutr. 2009 Feb 18.
Park Y, Brinton LA, Subar AF, Hollenbeck A, Schatzkin A. Dietary fiber intake and risk of breast cancer in postmenopausal women: the national Institutes of Health-AARP Diet and Health Study. Am J Clin Nutr. 2009;90(3):664-71.
Park Y, Subar A, Hollenbeck A, Schatzkin A. Dietary fiber intake and mortality in the NIH-AARP diet and health study. Arch Intern Med. 2011;171(12):1061-8.
Post R, Mainous A, King D, Simpson K. Dietary fiber for the treatment of type 2 diabestes mellitus; a meta-analysis. J Am Board Fam Med. 2012;25(1):16-23.
Rakel. Integrative Medicine. 3rd ed. Philadelphia, PA: Elsevier Saunders; 2012.
Saad R. Peripherally Acting Therapies for the Treatment of Irritable Bowel Syndrome. Gastroenterology Clinics. Philadelphia, PA: Elsevier Saunders; 2011:40(1).
Sawada N, Iwasaki M, Yamaji T, et al. Fiber intake and risk of subsequent prostate cancer in Japanese men. Am J Clin Nutr. 2015; 101(1):118-25.
Schatzkin A, Lanza E, Corle D, Lance P, Iber F, Caan B, et al. Lack of effect of a low-fat, high-fiber diet on the recurrence of colorectal adenomas. N Engl J Med. 2000;342(16):1149-1155.
Sola R, Godas G, Ribalta J, et al., Effects of soluble fiber (Plantago ovata husk) on plasma lipids, lipoproteins, and apolipoproteins in men with ischemic heart disease. Am J Clin Nutr. 2007;85(4):1157-63.
Soler M, Bosetti C, Franceschi S, Negri E, Zambon P, Talamini R, et al. Fiber intake and the risk of oral, pharyngeal, and esophageal cancer. Int J Cancer. 2001;91(3):283-287.
Stampfer MJ, Hu FB, Manson JE, Rimm EB, Willett WC. Primary prevention of coronary heart disease in women through diet and lifestyle. N Engl J Med. 2000;343(1):16-22.
Tariq N, Jenkins D, Vidgen E, Fleshner N, Kendall CW, Story JA, et al. Effect of soluble and insoluble fiber diets on serum prostate specific antigen in men. J Urol. 2000;163:114-118.
Terry P, Lagergren J, Ye W, Wolk A, Nyren O. Inverse association between intake of cereal fiber and risk of gastric cardia cancer. Gastroenterology. 2001;120(2):387-391.
Threapleton DE, Greenwood DC, Evans CE, et al. Dietary fiber intake and risk of first stroke: a systematic review and meta-analysis. Stroke. 2013;44(5):1360-8.
Tuomilehto J, Lindstrom J, Eriksson JG, Valle TT, Hamalainen H, Ilanne-Parikka P, et al. Prevention of type 2 diabetes mellitus by changes in lifestyle among subjects with impaired glucose tolerance. N Engl J Med. 2001;344(18):1343-1350.
Wei ZH, Wang H, Chen XY, Wang BS, Rong ZX, Wang BS, Su BH, Chen HZ. Time- and dose-dependent effect of psyllium on serum lipids in mild-to-moderate hypercholesterolemia: a meta-analysis of controlled clinical trials. Eur J Clin Nutr. 2008 Nov 5.
Yao B, Fang H, Xu W, et al. Dietary fiber intake and risk of type 2 diabetes: a dose-response analysis of prospective studies. Eur J Epidemiol. 2014;2992:79-88.
Zhang C, Liu S, Solomon CG, Hu FB. Dietary fiber intake, dietary glycemic load, and the risk for gestational diabetes mellitus. Diabetes Care. 2006;29(10):2223-30.
Zhang Z, Xu G, Ma M, Yang J, Liu X. Dietary fiber intake reduces risk for gastric cancer: a meta-analysis. Gastroenterology. 2013; 145(1):113-120.e3.