Fiber is the general term for those parts of plant food that we are unable to digest; however, bacteria present in the colon partly digests fiber through a process known as fermentation. Fiber is not found in foods of animal origin (meats and dairy products).

Types of Fiber:

Plant foods contain a mixture of different types of fibers. These fibers can be divided into soluble or insoluble, depending on their solubility in water.

1. Insoluble fibers (cellulose, hemicelluloses, and lignin)
   make up the structural parts of the cell walls of plants. These fibers absorb many times their own weight in water, creating a soft bulk to the stool, and hasten the passage of waste products out of the body. These insoluble fibers promote bowel regularity and aid in the prevention and treatment of some forms of constipation, hemorrhoids, and diverticulitis. These fibers also may decrease the risk of colon cancer by diluting potentially harmful substances that are present in the colon.
2. Soluble fibers (gums, pectins, and mucilages) are found within the plant cells. These fibers form a gel, which slows both stomach emptying and absorption of simple sugars from the intestines. This process helps to regulate blood sugar levels, which is particularly helpful in diabetic patients and is helpful in controlling weight In non-diabetics. Many soluble fibers can also assist in lowering blood cholesterol by binding with bile acids and cholesterol and eliminating the cholesterol through the intestinal tract before the cholesterol can be absorbed into the blood stream. Weight control is aided by the slower emptying of the stomach when you ingest soluble fibers. This causes a feeling of fullness and a decrease in hunger, causing fewer calories to be consumed. For example, if you eat an apple, which has a high fiber content, you’ll have a feeling of fullness, as compared to eating a cupcake, which has no fiber, and which is the same weight and size as the apple. In fact, it would take approximately three cupcakes to satisfy your brain’s hunger center before you realized that you were full. Well, by then you would already have consumed 480 calories and 16.5 grams of fat. The best sources of soluble fiber are fruits and vegetables, oat bran, barley, dried peas and beans, flax seed, and psyllium.
3. Resistant starch: Approximately 15% of the starch in foods is tightly bound to fiber and resists the normal digestive processes. Bacteria normally present in the colon ferment this resistant starch and change it into short-chain fatty acids, which are important to normal bowel health and may also help to protect the colon from cancer-causing agents. Foods that contain resistant starch include breads, cereals, pasta, rice, potatoes, and legumes.
4. Dietary fiber is a new measurement and refers to all fiber components of plants, including crude fiber. It is, therefore, a more accurate measurement of the fiber content of foods. The dietary fiber content consequently has a higher numerical reading than grams of crude fiber. Fiber, commonly known as bulk or roughage, is the part of plant foods that cannot be digested completely, so that it passes through the digestive tract intact. Therefore, dietary fiber is the fiber content of food, which is resistant to the human digestive enzymes.

The function of fiber: The most important function of dietary fiber is to bind water in the intestine, in the form of a gel. This gel prevents its over-absorption from the large intestine and ensures that the stool content of the large bowel is both bulky and soft, and, consequently, its passage through the intestine is not delayed. Another important function of fiber is its effect on the metabolism, absorption, and reabsorption of bile acids and cholesterol. Dietary fiber actually binds or attaches to both cholesterol and bile acid, and consequently decreases their absorption from the bowel. It is now recognized that there are a number of deases which are, at least in part, caused by a lack of dietary fiber. This
was first described in 1975 by Burkitt, P.O., and Trowell, H.C., eds. in Refined Carbohydrate Foods and Disease, New York (London). These diet-related diseases can be classified as follows:

1. Gastrointestinal disorders: Constipation, diverticulosis, appendicitis, hiatal hernia, hemorrhoids, cancer of the colon.
2. Metabolic disorders: Obesity, diabetes, gallstones.
3. Cardiovascular disorders: Arteriosclerosis (coronary artery disease), varicose veins, high blood pressure and
   strokes.
4. Degenerative disorders: Breast and prostate cancer, and
   neurological disorders including Alzheimer’s disease.

A recent study has shown that these diseases are now becoming prevalent in non-European communities, which have introduced Western dietary customs. There is almost an inverse relationship between the amount of fiber consumed and the prevalence of the various diseases in different countries. The higher the intake of dietary fiber, the lower the incidence of the above named disorders.

The latest medical report on high fiber foods indicates that there are cancer-protecting substances called phyto-nutrients actually contained in some dark green and dark yellow vegetables and fruits. One substance, known as beta-carotene (a nutrient that the body converts into vitaminA), is found in high concentration in spinach, carrots, broccoli, Brussels sprouts, cauliflower, winter squash, cabbage, oranges, grape-fruit, apricots, and peaches. These high-fiber foods also contain large amounts of vitamin C. Both vitamins may possibly be protective against cancer of the lung, esophagus, stomach, large bowel, and skin.

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