Dietary Fiber Information

Dietary Fiber Information….the advantages of consuming fiber are the production of healthy compounds during the fermentation of soluble fiber, and insoluble fiber’s ability to increase bulk, soften stool and shorten transit time through the intestinal tract.

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.

Legumes such as soybeans contain dietary fibers. Some plants contain significant amounts of soluble and insoluble dietary fiber. For example plums (or 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.



Dietary Fiber (sometimes called 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 dietary fiber source, lignin, may alter the metabolism of soluble fibers.

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

A novel position has been adopted by the US Department of Agriculture to include functional fibers as isolated fiber sources that may be included in the diet. The term “fiber” is somewhat of a misnomer, since many types of so-calleddietary fiber are not fibers at all.

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 vegetables such as potatoes, sweet potatoes, and onions (skins of these vegetables 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 such as green beans, cauliflower, zucchini (courgette), celery, and nopal
• some fruits including avocado, and bananas
• the skins of some fruits, including tomatoes

The five most fiber-rich plant foods, according to the Micronutrient Center of the Linus Pauling Institute, are legumes (15–19 grams of fiber per US cup serving, including several types of beans, lentils, and peas), bran (17 grams per cup), prunes (12 grams), Asian pear (10 grams each, 3.6% by weight), and 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 dietary fiber.