Types of Dietary Fiber and their Role in the Digestive Process

Fiber is a part of foods of vegetable origin which have no calories but play a very important role in the good health and wellbeing of the human body. Fiber is found in cereal grains, pulses and dhals, nuts, vegetables and fruits. It occurs in two forms soluble or non-fibrous fiber and insoluble or fibrous fiber.

Fiber is a component of the plant that cannot be digested by the enzymes produced in the human digestive tract. The insoluble fibers are mainly found in the cell walls of plants. They are called insoluble fibers because they do not dissolve in water. They however attract water and therefore speed up the elimination of waste products from the intestinal tract.

Their function is to prevent constipation, haemorrhoids and colon and rectal cancer. The chief sources of insoluble fiber are whole grain cereals. When cereals are consumed with their skin i.e. with the bran that covers them, this provides insoluble fiber. Whole wheat broken (dahlia) or whole wheat atta made into rotis or bread is an excellent source of insoluble fiber. Cornflakes and wheat flakes as well as ragi with the skin are also good sources.

The fruits that can be eaten with their skin or peal such as apples and pears, as well as strawberries and black berries are also good sources of insoluble fiber. Insoluble fiber is also present in skin of green pea, channa beans, rajma beans, kidney beans, etc. It is also present in nuts.
The scientific name for insoluble fiber is cellulose, hemicellulose and lignins. This fiber does not dissolve and increases the stool bulk preventing constipation. It speeds the passage of food residues through the large intestine and keeps the intestines in good order and reduces the risk of bowl disorders. This fiber also prevents the build-up of carcinogens which cause cancer.

Soluble fiber when mixed with water forms a gel like substance and swells up. The scientific names for soluble fibers include pectins, gums and mucilages. Good sources of this fiber are oats, oatmeal, barley, green beans, peas and most fruits and vegetables like oranges, apples, bananas, carrots, potatoes, etc. Soluble fiber helps to reduce blood cholesterol levels because it can bind to cholesterol in bile – the yellowish liquid secreted by the liver which helps to break down fats in the small intestine. Some cholesterol may then be removed with the fiber as waste rather than being reabsorbed. In the small intestine, soluble fiber also slows the absorption of glucose into the bloodstream preventing a sudden rise in blood sugar level which is particularly beneficial for diabetics.

While fiber has little or no nutritional value, it forms an essential link in the body’s digestive chain. Soluble and insoluble fibers are both important. Some plant foods provide both sorts – apple peel, for instance, is insoluble cellulose, while the flesh is an excellent source of the soluble fiber, pectin. We don’t need to worry too much about which type of fiber we are consuming but we need to make sure that there is at least 18-20 gms total fiber daily. This can be obtained by eating cereal food like oats, cornflakes, ragi or whole wheat bread, chapathi for breakfast, rice or rotis for lunch and whole wheat rotis for dinner. Dhals and pulses must be eaten for lunch and dinner. Vegetables cooked as well as salads must be eaten with both lunch and dinner and at least 1-2 fruits must be consumed daily.People should eat all 3 meals and see that cereals or carbohydrate food is present in all the meals. Diets which require you to avoid carbohydrate foods or consume only fruits salads or soups in any one meal can be very harmful and dangerous to the body.