Dietary fiber or roughage is a group of food particles which pass through stomach and small intestine, without being digested and reach the large intestine unchanged. Other nutritive substances of food are digested and absorbed before reaching large intestine. Characteristic feature of dietary fiber is that it is

not digestible by digestive enzymes. So it escapes digestion in small intestine and passes to large intestine. It provides substrate for microflora of large intestine and increases the bacterial mass. The anaerobic bacteria in turn, degrade the fermentable components of the fiber. Thus, in large intestine, some of the components of fiber are broken down and absorbed and remaining components are excreted through feces.

Components of Dietary Fiber

Major components of dietary fiber are cellulose, hemicelluloses, Dglucans, pectin, lignin and gums. Cellulose, hemicelluloses and pectin are partially degradable, while other components are indigestible.

Dietary fiber also contains minerals, antioxidants and other chemicals that are useful for health.

 Source of Dietary Fiber

Source of dietary fiber are fruits, vegetables, cereals, bread and wheat grain (particularly its outer layer).

Health Benefits of Dietary Fiber

1. By intake of high dietary fiber food, some diseaseproducing food substances may be decreased in

quantity or completely excluded in diet

2. Dietary fiber helps in weight maintenance because it requires more chewing and promotes hunger satisfaction by delaying the emptying of stomach and by giving the person a sense of fullness of stomach

3. Diet with high fiber content tends to be low in energy and it is also useful in reducing the body weight

4. Dietary fiber increases the formation of bulk and soft feces and eases defecation

5. It contains some useful substances such as antioxidants

6. Some components of dietary fiber also reduce blood cholesterol level and thereby, decrease the risk of

some diseases such as coronary heart disease and gallstones

7. Dietary fiber is also suggested to prevent or to treat some disorders such as constipation, bowel

syndrome, diabetics, ulcer and cancer.


Glucose is transported from the lumen of small intestine into the epithelial cells in the mucus membrane of small intestine, by means of sodium cotransport. Energy for this is obtained by the binding process of sodium ion and glucose molecule to carrier protein. From the epithelial cell, glucose is absorbed into the

portal vein by facilitated diffusion. However, sodium ion moves laterally into the intercellular space. From here, it is transported into blood by active transport, utilizing the energy liberated by breakdown of ATP.


Galactose is also absorbed from the small intestine in the same mechanism as that of glucose.


Fructose is absorbed into blood by means of facilitated diffusion. Some molecules of fructose are converted

into glucose. Glucose is absorbed as described above.


Metabolism is the process in which food substances undergo chemical and energy transformation. After digestion and absorption, food substances must be utilized by the body. The utilization occurs mainly by

oxidative process in which the carbohydrates, proteins and lipids are burnt slowly to release energy. This

process is known as catabolism. Part of the released energy is utilized by tissues for physiological actions and rest of the energy is stored as rich energy phosphate bonds and in the form of proteins, carbohydrates and lipids in the tissues. This process is called anabolism.

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