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 hydrolyzed 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, D-glucans, 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.

Sources of Dietary Fiber

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

Significance of Dietary Fiber

Diet with high dietary fiber has health benefits since dietary fiber:

1. Delays emptying of stomach

2. Increases formation of bulk and soft feces and eases defecation

3. Contains substances such as antioxidants and other useful substances.

When high dietary fiber food is taken, other foods, which may cause some diseases may be decreased in

quantity or completely excluded from diet. Diet with high fiber content tends to be low in energy and it may be useful in reducing the body weight. Some components of dietary fiber also reduce blood cholesterol level and thereby decrease the risk for coronary heart disease and gallstones. Dietary fiber is suggested for treating or to prevent constipation and bowel syndrome. It is also useful in treatment of some disorders such as diabetics, cancer, ulcer, etc.



Diarrhea is the frequent and profuse discharge of intestinal contents in loose and fluid form. It occurs due

to the increased movement of intestine. It may be acute or chronic.


Normally, when digested food passes through colon, large portion of fluid is absorbed and only a semisolid stool remains. In diarrhea, the fluid is not absorbed sufficiently, resulting in watery bowel discharge. Acute diarrhea may be caused by temporary problems like infection and chronic diarrhea may be due to disorders of intestinal mucosa. Thus, the general causes of diarrhea are:

1. Dietary abuse: Diarrhea is caused by intake of contaminated water or food, artificial sweeteners

found in food, spicy food, etc.

2. Food intolerance: Acute diarrhea is caused mainly by indigestion of food substances, particularly

lactose, a sugar present in milk and milk products may not be digested easily

3. Infections by:

i. Bacteria such as Escherichia coli, Salmonella, Shigella, etc.

ii. Viruses like rotavirus, hepatitis virus, etc.

iii. Parasites like Entamoeba histolytica, Giardia lamblia, etc.

4. Reaction to medicines such as:

i. Antibiotics

ii. Antihypertensive drugs

iii. Antacids containing magnesium

iv. Laxatives

5. Intestinal diseases: Chronic diarrhea occurs during inflammation of intestine, irritable bowel syndrome

and abnormal motility of the intestine.


Severe diarrhea results in loss of excess water and electrolytes. This leads to dehydration and electrolyte

imbalance. Chronic diarrhea results in hypokalemia and metabolic acidosis. Other features of diarrhea are abdominal pain, nausea and bloating (a condition in which the subject feels the abdomen full and tight due to excess intestinal gas).


Failure of voiding of feces, which produces discomfort is known as constipation. It is due to the lack of movements necessary for defecation. Due to the absence of mass movement in colon, feces remain in

the large intestine for a long time, resulting in absorption of fluid. So the feces become hard and dry.


1. Dietary causes

Lack of fiber or lack of liquids in diet causes constipation.

2. Irregular bowel habit

Irregular bowel habit is most common cause for constipation. It causes constipation by inhibiting the

normal defecation reflexes.

3. Spasm of sigmoid colon

Spasm in the sigmoid colon (spastic colon) prevents its motility, resulting in constipation.

4. Diseases

Constipation is common in many types of diseases.

5. Dysfunction of myenteric plexus in large intestine – megacolon

Megacolon is the condition characterized by distension and hypertrophy of colon, associated with constipation. It is caused by the absence or damage of ganglionic cells in myenteric plexus, which causes dysfunction of myenteric plexus. It leads to accumulation of large quantity of feces in colon. The colon is distended to a diameter of 4 to 5 inch. It also results in hypertrophy of colon. Congenital development of megacolon is called

Hirschsprung disease.

6. Drugs

The drugs like diuretics, pain relievers (narcotics), antihypertensive drugs (calcium channel blockers),

anti parkinson drugs, antidepressants and the anticonvulsants cause constipation.

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