Fiber

Overview

Dietary fiber is a general term that refers to a wide variety of compounds from plants that are resistant to the digestive enzymes produced by humans. Because dietary fiber is resistant to digestive enzymes, it is not broken down or absorbed, which means it does not provide calories or energy to the body. In general, dietary fibers are various forms of complex carbohydrates that have varying abilities to swell by absorbing water into their structural matrix. Fibers that can actually dissolve in water, such as pectin, gums, and psyllium, are referred to as soluble fiber. Insoluble fibers or roughage cannot dissolve in water but they can absorb water. This causes them to swell, making them good bulking agents, which speeds up transit time and improves elimination. Examples of insoluble fibers are cellulose, hemicelluloses, and lignins.

Soluble fiber mixes with water, turning into a gel-like substance in the process as it passes through the gastrointestinal tract. Soluble fibers have a moderate cholesterol-lowering effect (1) and they also slow the absorption of glucose from the intestines and help regulate blood sugar levels. (2) The results of numerous studies indicate that people and/or cultures with high fiber diets reduce their risk of colorectal cancer by more than 30%. (3) , (4)

When the non-digestible fibers reach the colon, anaerobic bacteria degrade them in a process called fermentation. This process produces byproducts known as short-chain fatty acids, which help maintain proper acid/base balance in the colon and may also play a role in the prevention of colorectal cancer. (5)

In general, high fiber diets are associated with significantly reduced risks of cardiovascular disease, (6) cancer, and all cause mortality. (7) , (8) , (9) It is generally recommended that Americans should strive to achieve a total dietary fiber intake of 25 to 30 grams/day, which should preferentially come from foods, not supplements. However, dietary surveys indicate that dietary fiber intake among adults in the United States averages about 15 grams/day, or approximately half the recommended amount. (10)

Dosage Info

Dosage Range

The variety of different kinds of fiber supplements available makes it difficult to suggest dosages.

Most Common Dosage

The variety of different kinds of fiber supplements available makes it difficult to suggest dosages.

Dosage Forms

Tablets, capsules, and bulk powder.

Adult RDI

None established

Adult ODA

None established

Active Forms

Soluble fibers such as pectin, gums, and psyllium; insoluble fibers such as cellulose, hemicelluloses, and lignins.

Absorption

In general, dietary fiber and fiber supplements are not digested or absorbed by humans.

Toxicities & Precautions

General

There are no known toxicities associated with taking fiber supplements.

Side Effects

Ingesting large amounts of fiber within a short period of time can cause some individuals to experience minor side effects such as gas, bloating and intestinal cramps. These symptoms are almost always alleviated by initially backing off, and then gradually increasing the amount of fiber.

Functions in the Body

Dietary fiber

Dietary fiber contributes bulk to the intestinal content (both wet weight and volume) and helps speed up fecal transit time. (11)

Soluble types of dietary fiber

Soluble types of dietary fiber are more capable of binding to carcinogens, bile acids, and other toxic substances, which decreases the interaction of these compounds with the colonic tissues. (12) , (13)

Fiber-rich diets

Fiber-rich diets generally help to improve glycemic control and the regulation of blood sugar. (14)

Soluble fibers

Soluble fibers alter and help regulate the metabolism of lipoproteins and cholesterol, which helps to lower LDL-cholesterol levels. (15)

Clinical Applications

Diabetes, Type 2

Dietary fiber intake has been associated with a lower risk of type 2 diabetes. (16) Studies involving patients with type 2 diabetes reported that increased fiber in their diet improved blood glucose and lipid values. (17) , (18)

Diabetes, Type 1

High fiber diets can help improve glycemic control and reduce the number of hypoglycemic events experienced by patients with type 1 diabetes. (19)

Diverticulosis

Low fiber diets increase the risk of developing diverticular disease. (20) One of the most important aspects of treatment for patients with asymptomatic diverticulosis is education regarding the importance of increasing dietary fiber intake. (21)

Constipation

Consumption of low-fiber diets are associated with constipation in children (22) and the elderly. (23) Additional fiber is one of the most important natural treatment recommendations along with extra hydration and exercise. (24)

Elevated Cholesterol

Various types of soluble fiber results in relatively small but significant lowering of total cholesterol and LDL-cholesterol. (25) Results from a meta-analysis of 10 trials reported that the addition of 3 grams or more of soluble fiber to the daily diet enabled individuals with hypercholesterolemia to achieve a modest lowering of plasma cholesterol levels. (26) In a larger meta-analysis, 68 of 77 human studies reviewed (88%) reported that soluble fiber results in a lowering of total cholesterol and 41 of 49 studies (84%) reported significant reductions in LDL-cholesterol. (27)

Hemorrhoids

Increasing the intake of dietary fiber is one of the primary life style recommendations for the patients with hemorrhoids. (28) In one study, patients with internal bleeding hemorrhoids who were treated with a commercially available fiber supplement for 15 days experienced a substantial reduction in the frequency of bleeding episodes and the number of congested hemorrhoids present compared to controls. Also, additional improvements were noted at an evaluation 15 days after the fiber supplementation ended. (29)

Weight Management

High fiber diets may help protect against obesity according to the results of a study that followed young adults for a period of ten years. Individuals who consumed the least dietary fiber gained 8 pounds more over the 10-year period compared to individuals who consumed at least 21 grams of fiber daily. (30)

Symptoms and Causes of Deficiency

A lack of fiber is usually the result of poor food choices, which results in a diet that is deficient in fiber-containing foods. Consuming a diet lacking in fiber increases the risk of developing gastrointestinal problems such as constipation, diverticular disorders, and alterations in glycemic control.

Dietary Sources

Foods that are rich in soluble fiber include apples, citrus fruits, pears, carrots, onions, sweet potatoes, squash, legumes, and grains such as barley, oats, oat bran and oatmeal.

Foods high in insoluble fiber include whole-wheat breads, wheat cereals, wheat bran, rye, rice, barley, most other grains, potatoes, flaxseeds, and vegetables such as cabbage, beets, carrots, Brussels sprouts, turnips, and cauliflower.

References

  1. View Abstract: Fernandez ML. Soluble fiber and nondigestible carbohydrate effects on plasma lipids and cardiovascular risk. Curr Opin Lipidol. Feb2001;12(1):35-40.
  2. View Abstract: Ou S, Kwok K, Li Y, Fu L. In vitro study of possible role of dietary fiber in lowering postprandial serum glucose. J Agric Food Chem. Feb2001;49(2):1026-9.
  3. View Abstract: Jansen MC, Bueno-de-Mesquita HB, Buzina R, et al. Dietary fiber and plant foods in relation to colorectal cancer mortality: the Seven Countries Study. Int J Cancer. Apr1999;81(2):174-9.
  4. View Abstract: Howe GR, Benito E, Castelleto R, et al. Dietary intake of fiber and decreased risk of cancers of the colon and rectum: evidence from the combined analysis of 13 case-control studies. J Natl Cancer Inst. 1992;84:1887-1896.
  5. View Abstract: Scheppach W, Luehrs H, Menzel T. Beneficial health effects of low-digestible carbohydrate consumption. Br J Nutr. Mar2001;85(Suppl 1):S23-30.
  6. View Abstract: Negri E, La Vecchia C, Pelucchi C, Bertuzzi M, Tavani A. Fiber intake and risk of nonfatal acute myocardial infarction. Eur J Clin Nutr. Mar2003;57(3):464-70.
  7. View Abstract: Kromhout D, Bosschieter EB, de Lezenne Coulander C. Dietary fibre and 10-year mortality from coronary heart disease, cancer, and all causes: the Zutphen Study. Lancet. 1982;1:518-522.
  8. View Abstract: Mattisson I. Intakes of plant foods, fibre and fat and risk of breast cancer--a prospective study in the Malmo Diet and Cancer cohort. Br J Cancer. Jan2004;90(1):122-7.
  9. View Abstract: Slattery ML. Plant foods, fiber, and rectal cancer. Am J Clin Nutr. Feb2004;79(2):274-81.
  10. View Abstract: Alaimo K, McDowell M, Briefel R, Bischof A, Caughman C, Loria C, Johnson C. Dietary intake: vitamins, minerals and fiber of persons age two months and over in the United States: third National Health and Nutrition Examination Survey: phase 1, 1988-91. Advance Data. 1994;258:1-28.
  11. View Abstract: Saito T, Hayakawa T, Nakamura K, et al. Fecal output, gastrointestinal transit time, frequency of evacuation and apparent excretion rate of dietary fiber in young men given diets containing different levels of dietary fiber. J Nutr Sci Vitaminol. Oct1991;37(5):493-508.
  12. View Abstract: Ferguson LR, Roberton AM, Watson ME, et al. The adsorption of a range of dietary carcinogens by alpha-cellulose, a model insoluble dietary fiber. Mutat Res. Dec1993;319(4):257-66.
  13. View Abstract: Jacobs LR. Modification of experimental colon carcinogenesis by dietary fibers. Adv Exp Med Biol. 1986;206:105-18.
  14. View Abstract: Jenkins DJ, Jenkins AL. Dietary fiber and the glycemic response. Proc Soc Exp Biol Med. Dec1985;180(3):422-31.
  15. View Abstract: Fernandez ML. Soluble fiber and nondigestible carbohydrate effects on plasma lipids and cardiovascular risk. Curr Opin Lipidol. Feb2001;12(1):35-40.
  16. View Abstract: Schulze MB, Liu S, Rimm EB, Manson JE, Willett WC, Hu FB. Glycemic index, glycemic load, and dietary fiber intake and incidence of type 2 diabetes in younger and middle-aged women. Am J Clin Nutr. Aug2004;80(2):348-56.
  17. View Abstract: Chandalia M, Garg A, Lutjohann D, et al. Beneficial effects of high dietary fiber intake in patients with type 2 diabetes mellitus. N Engl J Med. May2000;342(19):1392-8.
  18. View Abstract: Anderson JW, Allgood LD, Turner J, et al. Effects of psyllium on glucose and serum lipid responses in men with type 2 diabetes and hypercholesterolemia. Am J Clin Nutr. Oct1999;70(4):466-73.
  19. View Abstract: Giacco R, Parillo M, Rivellese AA, et al. Long-term dietary treatment with increased amounts of fiber-rich low-glycemic index natural foods improves blood glucose control and reduces the number of hypoglycemic events in type 1 diabetic patients. Diabetes Care. Oct2000;23(10):1461-6.
  20. View Abstract: Halphen M, Blain A. Natural history of colonic diverticulosis. Rev Prat. Apr1995;45(8):952-8.
  21. View Abstract: Eggenberger JC. Diverticular Disease. Current treatment options in gastroenterology. Dec1999;2(6):507-516.
  22. View Abstract: Roma E, Adamidis D, Nikolara R, et al. Diet and chronic constipation in children: the role of fiber. J Pediatr Gastroenterol Nutr. Feb1999;28(2):169-74.
  23. View Abstract: Kovach T. Managing geriatric chronic constipation. Home Healthc Nurse. Sep1992;10(5):57-8.
  24. View Abstract: Soffer EE. Constipation: an approach to diagnosis, treatment, referral. Cleve Clin J Med. Jan1999;66(1):41-6.
  25. View Abstract: Brown L, Rosner B, Willett WW, Sacks FM. Cholesterol-lowering effects of dietary fiber: a meta-analysis. Am J Clin Nutr. Jan1999;69(1):30-42.
  26. View Abstract: Ripsin CM, Keenan JM, Jacobs DR, et al. Oat products and lipid lowering. A meta-analysis. JAMA. Jun1992;267(24):3317-25.
  27. View Abstract: Glore SR, Van Treeck D, Knehans AW, Guild M. Soluble fiber and serum lipids: a literature review. J Am Diet Assoc. Apr1994;94(4):425-36.
  28. View Abstract: Otto P, Otto JU. Hemorrhoidal diseases. Schweiz Rundsch Med Prax. Nov1994;83(44):1225-8.
  29. View Abstract: Perez-Miranda M, Gomez-Cedenilla A, Leon-Colombo T, et al. Effect of fiber supplements on internal bleeding hemorrhoids. Hepatogastroenterology. Nov1996;43(12):1504-7.
  30. View Abstract: Ludwig DS, Pereira MA, Kroenke CH, et al. Dietary fiber, weight gain, and cardiovascular disease risk factors in young adults. JAMA. Oct1999;282(16):1539-46.