ROUGHAGE

Dietary fiber or Dietary fibre or sometimes roughage is the indigestible portion of plant foods having two main components:

§  Soluble (prebiotic, viscous) fiber that is readily fermented in the colon into gases and physiologically active byproducts, and

§  Insoluble fiber that is metabolically inert, absorbing water throughout the digestive system and easing defecation

It acts by changing the nature of the contents of the gastrointestinal tract, and by changing how other nutrients and chemicals are absorbed.

Soluble fiber absorbs water to become a gelatinous, viscous substance and is fermented by bacteria in the digestive tract.

Insoluble fiber has bulking action and is not fermented, although a major dietary insoluble fiber source, lignin, may alter the fate and metabolism of soluble fibers.

Chemically, dietary fiber consists of non-starch polysaccharides such as arabinoxylans, cellulose and many other plant components such as resistant dextrins, inulin, lignin, waxes, chitins, pectins, beta-glucans and oligosaccharides.

Food sources of dietary fiber are often divided according to whether they provide (predominantly) soluble or insoluble fiber. Plant foods contain both types of fiber in varying degrees, according to the plant's characteristics.

Advantages of consuming fiber are the production of salubrious compounds during the fermentation of soluble fiber, and insoluble fiber's ability (via its passive hydrophilic properties) to increase bulk, soften stool and shorten transit time through the intestinal tract.

SOURCES OF FIBER

Dietary fiber is found in plants. While all plants contain some fiber, plants with high fiber concentrations are generally the most practical source.

Fiber-rich plants can be eaten directly. Or, alternatively, they can be used to make supplements and fiber-rich processed foods.

PLANT SOURCES OF FIBER 

Legumes such as soybeans contain dietary fibers.

Some plants contain significant amounts of soluble and insoluble fiber.

Example   :   Plums (Prunes) have a thick skin covering a juicy pulp. The plum's skin is an example of an insoluble fiber source, whereas soluble fiber sources are inside the pulp.

Soluble Fiber is found in varying quantities in all plant foods, including   :

§  Legumes (peas, soybeans, and other beans)

§  Oats, rye, chia, and barley

§  Some fruits and fruit juices (including prune juice, plums, berries, bananas, and the insides of apples and pears)

§  Certain vegetables such as broccoli, carrots, and Jerusalem artichokes

§  Root tubers and root vegetables such as sweet potatoes and onions (skins of these are sources of insoluble fiber)

§  Psyllium seed husk (a mucilage soluble fiber).

Sources of Insoluble Fiber include   :

§  Whole grain foods

§  Wheat and corn bran

§  Nuts and seeds

§  Potato skins

§  Flax seed

§  Lignans

§  Vegetables - green beans, cauliflower, zucchini, celery

§  Some fruits including avocado, and bananas

§  The skins of some fruits, including tomatoes

The 5 most fiber-rich plant foods, according to the Micronutrient Center of the Linus Pauling Institute, are

1)     Legumes (15–19 grams per US cup serving)

2)     Bran (17 grams per cup)

3)     Prunes (12 grams)

4)     Asian pear (10 grams each, 3.6% by weight)

5)     Quinoa (9 grams)

Rubus fruits such as raspberry (8 grams of fiber per serving) and blackberry (7.4 grams of fiber per serving) are exceptional sources of fiber. 

DIETARY FIBER FUNCTIONS AND BENEFITS

GUIDELINES ON FIBER INTAKE

The United States National Academy of Sciences, Institute of Medicine, suggest that adults should consume 20–35 grams of dietary fiber per day.

The British Nutrition Foundation has recommended a minimum fiber intake of 18 g/day for healthy adults.