Dietary fiber

From Free net encyclopedia

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

Contents 1 Uses 2 Harmful effects 3 Guidelines on fiber intake 4 Sources of fiber 5 Fiber supplements 5.1 Psyllium husk 5.2 Methylcellulose 5.3 Polycarbophil 5.4 Vegetable gums 6 See also 7 Further reading 8 References 9 External links

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 gel in 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 salts which may reduce blood cholesterol levels. It also may slow the absorption of glucose from the intestine, thereby requiring less insulin secretion.

Fiber may decrease spasms in the gastrointestinal tract by keeping the lumen distended. The main value of dietary fiber is that it provides bulk to the bolus moving 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 system to move it through, and the bulkier stool also tends to retain normal amounts of moisture to 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 cholesterol and 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 Medicine of over 88,000 women did not show a statistically significant relationship between higher fiber consumption and lower rates of colorectal cancer or adenomas.Template:Ref

Harmful effects

Negative effects of dietary fiber include a reduced absorption of vitamins, minerals, proteins, and calories from 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 at the same time as, or soon before or after, taking vitamin or mineral supplements.

Sometimes the excess of coarse dietary fiber causes the ileocecal valve to be stuck open or closed.

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 child was that intake should equal (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 pain should see a physician. Certain bulking agents are not commonly recommended with the prescription of opioids because the slow transit time mixed with larger stools may lead to severe constipation, pain, or obstruction.

The British Nutrition Foundation has 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, synergy between 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 broccoli and carrots
• root vegetables, such as potatoes and yams (the skins are insoluble fiber)
• psyllium seed (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 grain foods
• bran
• nuts and 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 cholesterol levels, reducing the risk of colon cancer, or losing weight. Soluble fiber supplements are particularly beneficial for Irritable Bowel Syndrome symptoms 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 disease and ulcerative colitis, and Clostridium difficile (May, 1994), due to the short-chain fatty acids they produce, and subsequent anti-inflammatory actions upon the bowel.

Psyllium husk

Psyllium seed husk (best known under the brand Metamucil). 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 can be misleading, because it can also help diarrhea and it does not cause bowel dependency.

Because bacteria that 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 FDA allows foods containing 0.75 g of psyllium husk fiber or 1.7 g of 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 bloating than 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 Wyeth Corporation'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).

See also

• Prebiotic - indigestible matter which encourages growth of gut flora

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. Template:NoteFuchs, 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, I., "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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