Dietary fiber

Dietary fibers are the indigestible portion of plant foods that move food through the digestive system and absorb water.

Uses

There are two principal types of dietary fiber: soluble and insoluble. Insoluble fiber is simply bulk that changes little as it passes through the body. Soluble fiber, on the other hand, forms a soft gelin solution with water. Most foods provide a mixture of both, but are listed as mostly one or the other. Soluble fiber has been shown to be able to bind bile saltswhich may reduce blood cholesterollevels. It also may slow the absorption of glucosefrom the intestine, thereby requiring less insulinsecretion.

Fiber may decrease spasms in the gastrointestinal tract by keeping the lumendistended. The main value of dietary fiber is that it provides bulk to the bolusmoving through the digestive tract. There are two great advantages to this: by bulking up the bolus, eventually increasing the weight of the stool, it's easier for the digestive systemto move it through, and the bulkier stool also tends to retain normal amounts of moistureto make it easier to eliminate with less straining and abrasion. The moisture content of human stool does not change when more fiber is consumed, except marginally from psyllium husk (Eastwood et. al & Prynne et. al). Because the bowel regulation is mostly due to bulking and not to increased water in the stool, it is very unlikely to cause diarrhea unless taken in massive amounts (this is as long as one does not consider synthetic sugars in this category).

Increased fiber consumption appears to lower the risk of developing type II diabetes, heart disease, and diverticulitis. [1]It may also help prevent high cholesteroland help fight obesity. High-fiber foods help move waste through the digestive tract faster and easier, so possibly harmful substances do not have as much contact with the gastrointestinal tract and reduce straining. Many cause blood sugar or cholesterol absorption to decrease in amplitude of the plotted absorption or decrease the amount absorbed by slowing or decreasing the absorption.

Although for years dietary fiber has been said to reduce the risk of colon cancer, one study conducted by researchers at the Harvard School of Medicineof over 88,000 women did not show a statistically significant relationship between higher fiber consumption and lower rates of colorectal cancer or adenomas.^{[{{fullurl:Template:FULLPAGENAME}}#endnote_<1>]}

Harmful effects

Negative effects of dietary fiber include a reduced absorption of vitamins, minerals, proteins, and caloriesfrom the gut. Some insoluble fibers can bind to certain minerals: calcium, magnesium, phosphorus, and iron. This is unlikely to be harmful in the average adult, but guidelines for the US have been established, and fiber users are advised to avoid taking an insoluble fiber supplement with or close to (in time) vitamin or mineral supplements.

Guidelines on fiber intake

The American Dietetic Association(ADA) recommends a minimum of 20-35 g/day for a healthy adult depending on calorie intake (e.g., a 2000 cal/8400 kj diet should include 25 g of fiber per day). The ADA's recommendation for a childwas that intake should equal their age in years plus 5 g/day for children (example a 4 year old should consume 9 g/day). No guidelines have yet been established for the elderly or very ill. Patients with current constipation, vomiting, and abdominal painshould see a physician. Certain bulking agents are not commonly recommended with the prescription of opioidsbecause the slow transit time mixed with larger stools may lead to severe constipation, pain, or obstruction.

The British Nutrition Foundationhas recommended a minimum fiber intake of 12-24 g/day for healthy adults. [2]

Sources of fiber

Current recommendations suggest that adults consume 20-35 grams of dietary fiber per day, but the average American's daily intake of dietary fiber is only 14-15 grams. [3]The ADA recommends trying to get most of your dietary fiber from foods you eat, as an important part of consuming variety, nutrition, synergybetween nutrients, and possibly phytonutrients. Soluble fiber is found in many foods, including:

• legumes, (peas, soybeans, and other beans)
• oats
• some fruits(particularly apples, bananas), and berries
• certain vegetables, such as broccoliand carrots
• root vegetables, such as potatoesand yams(the skins are insoluble fiber)
• psylliumseed (only about 2/3 soluble fiber).

Legumes also typically contain shorter-chain carbohydrates that are indigestible by the human digestive tract but which are digested by bacteria in the small intestine, which is a cause of flatulence.

Sources of insoluble fiber include

• whole grainfoods
• bran
• nutsand seeds
• vegetables such as green beans, cauliflower, zucchini, celery
• the skins of some fruits, including tomatoes

Fiber supplements

There are many types of soluble fiber supplements available to consumers for nutritional purposes, for the treatment of various gastrointestinal disorders, and for such possible health benefits as lowering cholesterollevels, reducing the risk of colon cancer, or losing weight. Soluble fiber supplements are particularly beneficial for Irritable Bowel Syndromesymptoms such as diarrhea and/or constipation, and abdominal pain (Van Vorous, 2000). Prebiotic soluble fiber supplements (acacia, FOS, inulin) are a promising area of treatment for inflammatory bowel disease(Seidner, 2005) such as Crohn's diseaseand ulcerative colitis, and Clostridium difficile (May, 1994), due to the short-chain fatty acids they produce, and subsequent anti-inflammatory actions upon the bowel.

Psylliumhusk

Psyllium husk (best known under the brand Metamucilfrom Procter & Gamble, but also available generically) is a good source of both soluble and insoluble fiber. It is low in calories, is available in powders and in capsules, and must be taken with water to avoid a risk of choking. Psyllium husk may reduce the risk of heart disease by lowering cholesterol levels, and is known to help alleviate the symptoms of irritable bowel syndrome, though it often causes uncomfortable bloating. Psyllium husk is often labeled a "bulk-forming laxative," which is misleading, because it can also help diarrhea and it does not cause bowel dependency.

Because bacteriathat occur naturally in the intestinal tract can digest the fiber in psyllium husk and cause it to ferment, psyllium husk fiber supplements can cause gas.

The FDAallows foods containing 0.75 g or 1.7 g of psyllium husk fiber or oat fiber to claim that they may be able to reduce the risk of heart disease(J Am Diet Assoc 2002).

Methylcellulose

Methylcellulose is created from the cell wall of plants. Sold as a powder, it is undigestible, unfermentable, and doesn't have calories that humans can use. Citrucel (by GlaxoSmithKline), and Celevac (Shire) are popular brands of methylcellulose.

Polycarbophil

Polycarbophil is also plant based and is similar to methylcellulose. It causes less bloatingthan psyllium husk and is effective for treating constipation, diarrhea, and Irritable Bowel Syndrome(Danhof, 1982). Polycarbophil is found in a large number of consumer brands, including WyethCorporation's Fibercon and Numark's Equalactin. It is also typically labeled a "bulk-forming laxative."

Vegetable gums

Vegetable gum fiber supplements are relatively new to the market. Often sold as a powder, vegetable gum fibers dissolve easily with no aftertaste. They are effective for the treatment of Irritable Bowel Syndrome(Parisi, 2002). Examples of vegetable gum fibers are guar gum (brand name Benefiber) or acacia (brand name Heather's Tummy Fiber).

Further reading

• Marlett JA. Dietary fiber and cardiovascular disease. In: Cho SS, Dreher ML, eds. Handbook of Dietary Fiber. New York: Marcel Dekker, Inc; 2001:17-30.
• US Food and Drug Administration. Health Claims: Soluble fiber from certain foods and risk of heart diseases. Code of Federal Regulations. 2001;21:101.81.
• Eastwood MA, Brydon WG. Tadesse K. Effect of fiber on colon function. In: Spiller GA, Kay RM, eds. Medical Aspects of Dietary Fiber. New York, NY: Plenum Press; 1980:1-26.
• Prynne CJ, Southgate DAT. The effects of a supplement of dietary fibre on faecal excretion by human subjects. Br J Nutr. 1979;41:495-503.

References

1. ^ Fuchs, CS, et al. "Dietary fiber and the risk of colorectal cancer and adenoma in women." New England Journal of Medicine, 21 Jan 1999:223-4.

• Mayo Clinic Health Letter , March 1998, copyrighted material
• Danhof, J., "Pharmacology, Toxicology, Clinical Efficacy and Adverse Effects of Calcium Polycarbophil, An External Hydrosorptive Agent," Pharmacotherapy Vol.2, No.1, Jan/Feb 1982.
• Donatelle, Rebecca J. Health: The Basics. 6th ed. San Francisco: Pearson Education, Inc. 2005.
• Parisi GC. High-fiber diet supplementation in patients with irritable bowel syndrome (IBS): a multicenter, randomized, open trial comparison. Dig Dis Sci. 2002 Aug;47(8):1697-704.
• Van Vorous, Heather. Eating for IBS. 2000. ISBN 1569246009. Copyrighted dietary fiber and Irritable Bowel Syndrome information excerpted with author's permission at Help for Irritable Bowel Syndrome - the IBS Diet
• ADA website
• ADA position paper - J Am Diet Assoc 2002;102:993-1000, copyrighted material

External links

• Database of Fiber-Containing Foods
• Alternative health site - Fiber & Diverticulosis
• ADA Position paper - J Am Diet Assoc 2002;102:993-1000de:Ballaststoff

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It uses material from the http://en.wikipedia.org/wiki/Dietary+fiber Wikipedia article Dietary fiber.