Dietary fiber, found in the walls of plant cells, cannot be digested by enzymes in the human digestive tract but plays an essential role in human health. It is found in all plant-based foods, with most whole foods containing a combination of the two types of fiber, including soluble and insoluble fiber. Both types of fiber help maintain the health of the intestinal tract and promote regular elimination of stool.

Soluble fiber attracts water and forms a gel in the digestive tract. This slows digestion and lowers the rate of nutrient absorption (such as starch and sugars) from the stomach and intestine. The result is a significant reduction in cholesterol levels over time, which may help prevent heart disease and stroke. Intake of soluble fiber may also improve glucose tolerance in people with diabetes. Psyllium husk, pectin, and the soft parts of fruits, dried beans, and peas are examples of soluble fiber.

Insoluble fiber, on the other hand, is the portion of plant cells that gives the wall its structural integrity. Insoluble fiber 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.

Dietary fiber has been shown to play a role in the treatment of conditions such as gastrointestinal disease, constipation, hemorrhoids, high cholesterol, heart disease, and diabetes. However, most Americans consume only 11 - 13 grams of dietary fiber per day -- less than half the amount recommended by health care professionals. It has been recommended that Americans should strive to achieve a total dietary fiber intake of 25 - 30 grams daily, preferably from foods and not supplements.

Constipation

Many well-designed clinical studies have concluded that fiber relieves constipation. Clinical studies have used wheat bran and psyllium primarily. Fiber is believed to relieve constipation by adding bulk to stool and speeding its transit through the gastrointestinal tract.

Diarrhea

When recommended by a health care provider, fiber can be used to relieve mild-to-moderate diarrhea. Soluble fiber soaks up a significant amount of water in the digestive tract, thereby making stool firmer and slower to pass.

Irritable bowel syndrome (IBS)

Several well-designed clinical studies have found that soluble fiber helps regulate stool frequency and consistency in people with IBS.

Hemorrhoids

Soluble fiber may be recommended by a doctor to help soften stool and reduce the pain associated with hemorrhoids.

Inflammatory bowel disease (IBD)

In a clinical study of people with ulcerative colitis (a type of IBD), psyllium seeds were as effective as the prescription drug mesalamine in reducing recurrences of the disease. In addition, a doctor may recommend the use of fiber as a bulking agent for mild-to-moderate cases of diarrhea from either ulcerative colitis or Crohn's disease (another important type of IBD).

Diverticulosis

Patients with diverticulosis are often given fiber supplements to increase the tone of their digestive tract. The American Dietetic Association (ADA) recommends 25 - 30 grams per day. Some nutritionally-oriented doctors may recommend even more. Care should be taken to discuss the appropriate type of fiber for each individual patient as certain types of fiber may actually aggravate diverticulosis. In particular, avoidance of nuts, pumpkin, caraway, and sesame seeds is recommend out of concern that the small particles may get lodged in the diverticula and cause infection and irritation.

High cholesterol

Soluble fibers, such as those in psyllium husk, guar gum, and oat bran, have a cholesterol-lowering effect when added to a low-fat, low-cholesterol diet. Clinical studies have shown psyllium, in particular, to be quite effective in lowering total as well as low density lipoprotein (LDL or "bad") cholesterol levels.

Diabetes

Clinical studies suggest that a high-fiber diet may help prevent type 2 diabetes, lower insulin and blood sugar levels, and improve cholesterol and triglyceride levels in people with diabetes. In addition, one well-designed clinical study suggests that pregnant women with type 1 diabetes are able to lower the amount of insulin they use if they eat a high fiber diet.

A clinical study compared patients with type 2 diabetes who were consuming 50 grams of fiber daily with patients following the American Diabetes Association’s recommendation of 24 grams of fiber daily. After 6 weeks, patients on the higher fiber diet had substantially 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 experienced significant improvements in blood glucose and lipid values compared to a control group taking a placebo.

Obesity

Clinical studies and human case reports suggest that soluble fiber (such as psyllium, pectin, and guar gum) may enhance the sensation of fullness and reduce hunger cravings. For these reasons, incorporating soluble fiber into the diet may aid weight loss.

High blood pressure

Although not entirely conclusive, the addition of fiber (namely, 12 grams of soluble fiber per day) may help lower blood pressure (also called hypertension).

Heart disease

Incorporating high-fiber foods (such as oatmeal, oat bran, psyllium, and legumes) into the diet may help lower heart disease risk.

Colon cancer

Although initial clinical reports were promising, studies investigating the value of a high-fiber diet for colorectal cancer have been conflicting. While some clinical studies evaluating groups of people have suggested that fiber protects against the development of colorectal cancer, most large, better-designed clinical studies have found only a minimal association between fiber intake and colorectal cancer risk. In addition, fiber does not appear 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 the development of certain types of cancer such as prostate, breast, and lining of the uterus. Further studies are needed to confirm these findings, however.

Soluble fiber is found in dried beans and peas, oats, barley, fruits, and psyllium seed husks.

Insoluble fiber is found primarily in fruits and vegetables, whole-grain products, whole grain cereals, and wheat and corn bran.

Dietary 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.

The National Academy of Sciences' Institute of Medicine, which provides science-based advice on matters of medicine and health, gives the following daily fiber recommendations for adults:

Pediatric

Infants and children under 18 years of age: There is no specific dietary amount established for pediatric fiber intake. Children with specific fiber needs should increase the daily intake of fibrous foods slowly over a period of days. Fiber supplements should only be taken under the guidance of a qualified health care practitioner.

Adults

For adult males ages 19 - 50: The recommended daily fiber intake amount is 38 grams.

For adult females ages 19 – 50: The recommended daily fiber intake amount is 25 grams.

For adult males ages 51 and older: The recommended daily fiber intake amount is 30 grams.

For adult females ages 51 and older: The recommended daily fiber intake amount is 21 grams.

If you are not getting enough fiber each day, you may need to boost your fiber intake in the 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, and rice, and non-whole-grain cereals, are lower in fiber content. The grain-refining process removes the outer coat (bran) from the grain, which lowers its fiber content. Similarly, removing the skin from fruits and vegetables decreases their fiber content.

Because supplements may have side effects or interact with medications, they should be taken only under the supervision of a knowledgeable health care provider.

In general, fiber supplements may reduce or delay the absorption of certain medications. For this reason, it is best to refrain from taking fiber supplements at the same time as other medications. Instead, medications should be taken at least 1 hour before or between 2 - 4 hours after taking fiber.

Fiber should always be taken with a full 8 oz glass of water. It is also important to drink at least 6 - 8 full glasses of water throughout the day or constipation may develop. Taking fiber supplements without adequate liquids may cause it to swell and, in extreme cases, 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 experience chest pain, vomiting, or difficulty swallowing or breathing after taking fiber supplements, seek immediate medical attention.

A potential side effect from any fiber product is gas and bloating.

Although very uncommon, allergic reactions (even anaphylaxis) to soluble fiber may develop in people who consume these types of supplements over a long period of time.

If you are currently being treated with any of the following medications, you should not use fiber supplements without first talking to your health care provider.

Antidepressant medications (Tricyclic antidepressants) -- Dietary fiber has been reported to lower the blood levels and effectiveness of tricyclic antidepressant medications, such as amitriptyline (Elavil), doxepin (Sinequan), and imipramine (Tofranil), in several patients. Reduced dietary fiber intake increased the blood levels and improved symptoms in these patients. Individuals currently taking tricyclic medications should consult a health care provider before increasing fiber intake.

Diabetes medications -- While fiber supplements may help to regulate blood sugar levels, they may also interfere with the absorption of anti-diabetic medications, specifically glyburide (Diabeta) and metformin (Glucophage). Therefore, fiber supplements should not be taken at the same time as these medications.

Carbamazepine -- Taking soluble fiber such as psyllium with carbamazepine (Tegretol), a medication used to treat seizure disorders, may decrease the absorption and effectiveness of carbamazepine. A health care provider should close monitor blood levels of anyone taking both soluble fiber and carbamazepine.

Cholesterol-lowering medications -- Combining psyllium or other soluble fibers with cholestyramine (Questran) or colestipol (Colestid), two types of cholesterol-lowering medications known as bile acid sequestrants, may be beneficial in lowering cholesterol levels. Individuals taking these medications should consult a health care provider to determine whether psyllium is safe and appropriate.

Fiber in the form of pectin (from fruit) and oat bran reportedly reduces the body's ability to absorb cholesterol-lowering medications known as "statins," including lovastatin (Mevacor) and atorvastatin (Lipitor), and could lead to decreased effectiveness of these medications.

Digoxin -- Fiber supplements may reduce the body's ability to absorb digoxin (Lanoxin), a medication used to regulate heart function. Therefore, fiber supplements should not be taken at the same time as this medication.

Lithium -- Clinical reports suggest that psyllium or other soluble fibers may lower lithium levels in the blood, reducing the effectiveness of this medication. Lithium levels should be monitored very closely by a health care provider, particularly if there is any significant change in fiber intake.

Penicillin -- In one clinical study, the fiber supplement guar gum reduced blood levels of penicillin. Therefore, it would be best not to take penicillin at the same time as fiber supplements.

Alabaster O, Tang ZC, Frost A, Sivapurkar N. Potential synergism between wheat brain and psyllium: enhanced inhibition of colon cancer. Cancer Lett. 1993;75:53–58.

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.

American Diabetes Association. Nutrition recommendations and principles for people with diabetes mellitus. Diabetes Care. 1999;22(1):S42-S45.

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, Allgood LD, Turner J, Oeltgen PR, Daggy BP. Effects of psyllium on glucose and serum lipid responses in men with type 2 diabetes and hypercholesterolemia. Am J Clin Nutr. 1999;70:466-473.

Appel LJ. Nonpharmacologic therapies that reduce blood pressure: a fresh perspective. Clin Cardiol. 1999;22(Suppl. III):III1-III5.

Ashraf W, Park F, Lof J, Quigley EM. Effects of psyllium therapy on stool characteristics, colon transit and anorectal function in chronic idiopathic constipation. Aliment Pharmacol Ther. 1995;9:639–647.

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.

Brown L, Rosner B, Willett WW, Sacks FM. Cholesterol-lowering effects of dietary fiber: a meta-analysis. Am J Clin Nut. 1999;69(1):30-42.

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.

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.

Cohen LA. Dietary fiber and breast cancer. Anticancer Res. 1999;19(5A):3685-3688.

Compher CW, Frankel WL, Tazelaar J, Lawson JA, McKinney S, Segall S, et al. Wheat bran decreases aberrant crypt foci, preserves normal proliferation, and increases intraluminal butyrate levels in experimental colon cancer. JPEN: J Paren Enteral Nutr. Sep-Oct 1999;23(5):269-277.

Etman MA. Effect of a bulk forming laxative on the bioavailability of carbamazepine in man. Drug Dev Ind Pharm. 1995;21(16):1901-1906.

Ettinger AB, Shinnar S, Sinnett MJ, Moshe SL. Carbamazepine-induced constipation. J Epilepsy. 1992;5(3):191-193.

Fernandez-Banares F, Hinojosa J, Sanchez-Lombrana JL, et al. Randomized clinical trials of Platago ovata seeds (dietary fiber) as compared with mesalamine in maintaining remission in ulcerative colitis. Am J Gastroenterol. 1999;94:427–433.

Gallaher DD, Schneeman BO. Dietary fiber. In: Ziegler EE, Filer LJ, eds. Present Knowledge in Nutrition. 7th ed. Washington, DC: International Life Sciences Institute; 1996:87-94.

Gin H, Orgerie MB, Aubertin J. The influence of guar gum on absorption of metformin from the gut in healthy volunteers. Horm Metab Res. 1989;21(2):81-83.

Goodman MT, Wilkens LR, Hankin JH, Lyu LC, Wu AH, Kolonel LN. Association of soy and fiber consumption with the risk of endometrial cancer. Am J Epidemiol. 1997;146(4):294-306.

Gray DS. The clinical uses of dietary fiber. Am Fam Physician. 1995;51(2):419-426.

Hayes RB, Ziegler RG, Gridley G, et al. Dietary factors and risks for prostate cancer among blacks and whites in the United States. Cancer Epidemiol Biomarkers Prev. 1999;8(1):25-34.

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.

Hillemeier C. An overview of the effects of dietary fiber on gastrointestinal transit. Pediatr. 1995:997-999.

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.

Huupponen R, Seppala P, Iisalo E. Effect of guar gum, a fibre preparation, on digoxin and penicillin absorption in man. Eur J Clin Pharmacol. 1984;26(2):279-281.

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.

Jenkins DJ, Popovich DG, Kendall CW, Vidgen E, Tariq N, Ransom TP, et al. Effect of a diet high in vegetables, fruit, and nuts on serum lipids. Metabol. 1997;46(5):530-537.

Johnson BF, Rodin SM, Hoch K, Shakar V. The effect of dietary fiber on the bioavailability of digoxin in capsules. J Clin Pharmacol. 1987;27(7):487-490.

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.

Kritchevsky D. Dietary fibre and cancer. Eur J Cancer Prev. 1997;6:435-441.

Kurtz RC, Zhang ZF. Gastric cardia cancer and dietary fiber. Gastroenterology. 2001;120(2):568-70

Lantner RR, Espiritu BR, Zumerchik P, Tobin MC. Anaphylaxis following ingestion of a psyllium-containing cereal. JAMA. 1990;264(19):2534-2536.

Le Marchand L, Wilkens LR, Hankin JH, Kolonel LN, Lyu LC. Independent and joint effects of family history and lifestyle on colorectal cancer risk: Implications for prevention. Cancer Epidemiol Biomarkers Prevent. 1999;8:45-51.

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.

Ludwig DS, Pereira MA, Kroenke CH, Hilner JE, Van Horn L, Slattery ML, Jacobs DR Jr. Dietary fiber, weight gain, and cardiovascular disease risk factors in young adults. JAMA.1999:282(16):1529-1546.

Marlett JA, et al. Mechanism of serum cholesterol reduction by oat bran. Hepatology. 1994;20:1450-1457.

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.

McGuffin M, ed. American Herbal Products Association's Botanical Safety Handbook. Boca Raton, FL: CRC Press, 1997.

McRorie JW, Daggy BP, Morel JG, Diersing PS, Miner PB, Robinson M. Psyllium is superior to docusate sodium for treatment of chronic constipation. Aliment Pharmacol Ther. 1998;12:491–497.

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.

Murray MT, Pizzorno JE. Role of dietary fiber in health and disease. In: Pizzorno JE, Murray MT, eds. Textbook of Natural Medicine. Vol 1. 2nd ed. Edinburgh: Churchill Livingstone; 1999:507-516.

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.

Perlman BB. Interaction between lithium salts and ispaghula husk [letter]. Lancet. 1990;355:416.

Persson PG, Ahlbom A, Hellers G. Diet and inflammatory bowel disease: a case-control study. Epidemiol. 1992;3(1):47-52.

Potischman N, Swanson CA, Coates RJ, Gammon MD, Brogan DR, Curtin J, et al. Intake of food groups and associated micronutrients in relation to risk of early-stage breast cancer. Int J Cancer. 1999;82(3):315-321.

Richter WO, Jacob BG, Schwandt P. Interaction between fibre and lovastatin. Lancet. 1991;338;706.

Rodrigues-Moran M, Guerrero-Romero F, Lazcano-Burciaga G. Lipid- and glucose-lowering efficacy of Plantago Psyllium in type II diabetes. J Diabetes Complications. 1998;12:273–278.

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.

Shils ME, Olson JA, Shike M, eds. Modern Nutrition in Health and Disease. 9th ed. Media, Pa: Williams & Wilkins; 1999.

Soffer EE. Constipation: an approach to diagnosis, treatment, referral. Cleve Clin J Med. 1999;66(1):41-46.

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.

Spence JD, Huff MW, Heidenheim P et al. Combination therapy with colestipol and psyllium mucilloid in patients with hyperlipidemia. Ann Intern Med. 1995;123:493-499.

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.

Stewart DE. High-fiber diet and serum tricyclic antidepressant levels. J Clin Psychopharmacol. 1992;12:438-440.

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.

Toutoungi M, Schulz P, Widmer J, et al. Probable interaction of psyllium and lithium. Therapie. 1990;45(4):358-360.

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.

Turley SD, Daggy BP, Dietschy JM. Effect of feeding psyllium and cholestyramine in combination on low density lipoprotein metabolism and fecal bile acid excretion in hamsters with dietary-induced hypercholesterolemia. J Cardiovasc Pharmacol. 1996;27:71-79.

Turnbull WH, Thomas HG. The effect of a Plantago ovata seed containing preparation on appetite variables, nutrient and energy intake. Int J Obes Relat Metab Disord. 1995;19:338-342.

Vaswani SK, Hamilton RG, Valentine MD, Adkinson NF Jr. Psyllium laxative-induced anaphylaxis, asthma, and rhinitis. Allergy. 1996;51(4):266-268.

Wald A. Constipation. Med Clin North America. 2000;84(5):1231-1246.

Wursch P, Pi-Sunyer FX. The role of viscous soluble fiber in the metabolic control of diabetes. A review with special emphasis on cereals rich in beta-glucan. Diabetes Care. 1997; 20:1774-1780.

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.