Dietary fibers are the indigestible portion of plant foods that move food through the digestive system, absorbing water. Chemically, dietary fiber consists of non-starch polysaccharides and several other plant components such as cellulose, lignin, waxes, chitins, pectins, beta-glucans, inulin and oligosaccharides.
Sources of dietary fiber are usually divided according to whether they are water-soluble or not. Both types of fiber are present in all plant foods, with varying degrees of each according to a plant’s characteristics. Insoluble fiber possesses passive water-attracting properties that help to increase bulk, soften stool and shorten transit time through the intestinal tract. Soluble fiber undergoes active metabolic processing via fermentation, yielding end-products with broad, significant health effects.
Fibre is required as part of a healthy diet. In addition to keeping your bowel motions "regular", a high intake of fibre, especially soluble fibre, can help lower cholesterol levels. Dietary fibre also has a protective effect against colorectal cancer.
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 (e.g., a 4 year old should consume 9 g/day).
The British Nutrition Foundation has recommended a minimum fiber intake of 12-24 g/day for healthy adults.
Sources of fibre
Sources of Soluble fibre include:
* legumes (peas, soybeans, and other beans) * oats, rye, chia, and barley * some fruits (particularly apples, bananas), and berries * certain vegetables, such as broccoli and carrots * root vegetables, such as potatoes, yams and onions (skins of these vegetables are sources of insoluble fiber) * psyllium seed husk (a mucilage soluble fiber).
Legumes also typically contain shorter-chain carbohydrates indigestible by the human digestive tract but are metabolized by bacterial fermentation in the large intestine (colon), yielding short-chain fatty acids and gases (flatulence).
Sources of insoluble fibre include:
* whole grain foods * bran * nuts and seeds * vegetables such as green beans, cauliflower, zucchini, celery * the skins of some fruits, including tomatoes
There are many types of soluble fiber supplements available to consumers for nutritional purposes, treatment of various gastrointestinal disorders, and for such possible health benefits as lowering cholesterol levels, reducing risk of colon cancer, and losing weight.
Soluble fiber supplements may be beneficial for alleviating symptoms of irritable bowel syndrome, such as diarrhoea and/or constipation and abdominal discomfort.
Prebiotic soluble fiber products, such as those containing inulin or oligosaccharides, may contribute to relief from inflammatory bowel disease, such as Crohn's disease, ulcerative colitis, and Clostridium difficile, due in part to the short-chain fatty acids produced with subsequent anti-inflammatory actions upon the bowel.
Fiber supplements may be effective in an overall dietary plan for managing irritable bowel syndrome by modification of food choices.