What are the dietary fibers? /Importance of dietary fibers

Contents

1. Introduction to dietary fibers
2. The dietary fiber hypothesis
3. Classification of dietary fibers
4. Effects of dietary fibers on gut physiology
5. Interaction of dietary fibers with other nutrients
6. Common food items rich in dietary fibers
7. Other related topics

Introduction to dietary fibers

Although the importance of dietary fibers was recognized only a few decades ago, throughout the history a few perceptible individuals have from time to time drawn attention to the need for fiber in the diet. Hippocrates commented on the laxative effect of coarse flour. The Persian physician Hakim (9^th century AD) wrote: “whet is beneficial. Chappatis containing more bran come out of the digestive tract quicker but less nutritious. Those containing little bran take along time to be excreted”.

The dietary fiber hypothesis

The dietary fiber hypothesis has two primary statements;

1. A diet rich in foods containing plant cell walls (dietary fiber) is protective against a range of diseases prevalent in western communities.
2. In some instances a diet poor in foods containing plant cell walls is a causative factor in the development of the disease and, in others, it provides the conditions where other etiological factors are more active

Classification of dietary fibers

Dietary fiber was initially defined as the skeletal remains of plant cells in the diet that are resistant to hydrolysis by digestive enzymes of humans. The definition was later extended to all polysaccharides and lignin in the diet that are not digested by the endogenous secretions, so as to embrace polysaccharides in some food additives.

Dietary fibers may be classified according to their chemistry or their physical properties such as the water-holding capacity, viscosity and providers of gel filtration or cation exchange absorbent matrix or catalytic surface.

Chemical classification

1. Simple polysaccharides (cellulose)
2. Complex polysaccharides (Lignin, cutin)

Classification according to the physical properties

1. Water soluble Fibers(Cllulose)
2. Non-soluble fibers (Cutin)

The macromolecular constituents of plant cell wall material fall into 3 groups;

1. The fibrillar polysaccharides (cellulose)
2. The matrix polysaccharides ( hemicelluloses, glycoproteins)
3. The encrusting polysaccharides (lignin)

Effects of dietary fibers on gut physiology

The effects of dietary fibers on gut physiology will depend on the;

1. structure and tissue types
2. nature of the intracellular compounds
3. form in which the food is taken (fresh, cooked or processed)
4. food particle size

Dietary fiber acts in the small intestine in three main physical forms: as soluble chains, as insoluble macromolecular assemblies and as swollen, hydrated, sponge like net-work.

Dietary fiber helps to regulate 4 central aspects of the digestive process;

1. Nutrient absorption
2. Sterol metabolism
3. caecal fermentation
4. stool weight

Different fibers affect each of these processes in different ways.

Interaction of dietary fibers with other nutrients

Most, though not all, the results of feeding or administering various preparations of dietary fibers, particularly in the soluble gel forms indicate that dietary fibers modulate the absorption of nutrients in the small intestine. Following dietary components are mainly affected;

1. carbohydrates
2. lipids
3. minerals
4. vitamins

Common food items rich in dietary fibers

1. Vegetables ( leafy vegetables)
2. pulses
3. cereals
4. legumes
5. fruits (banana, mango)

Other related topics

1. Dietary fibers and related diseases
2. How does dietary fiber affect on nutrients absorption?
3. Bacterial flora and dietary fibers
4. Bile acids absorption and dietary fibers