Dietary ßber is deßned as that portion of plant material ingested in the diet that is resistant to digestion by gastro intestinal secretions. It consists of cellulose, hemicellulose, pectins, gums and mucilages as well as non-polysaccharide lignin.
Some bacteria in the large intestine can degrade some components of fibre releasing products, that can be absorbed into the body and used as energy source.
a. Cellulose : It is the main constituent of plant cell walls. It is found in all vegetables, fruits and legumes.
b. Hemicellulose: It is the main constituent of cereal fibres.It is also present in all vegetables and hulls of legumes.
c. Pectins: Pectins are formed by the combination of large number of galacturonic acid molecules. In the presence of sucrose and citric acid, pectin forms a gel. It is used in the food industry as an ingredient of jams and jellies
d. Gums and mucilages: They are non-structural components of plant cells that are soluble in hot water. They are used as additives and stabilizers by the food industry.
e. Lignin: They are the tough, woody parts of plants.
Dietary fibers can also be classified as soluble and insoluble fibers based on their solubility in water. Insoluble fibers do not dissolve in water(Cellulose,hemi-cellulose and lignin) and soluble fibres readily dissolve in water(Pectins, gums and mucilages).
The types, sources and action of fibre in the body is summarized in table 9.3
What’s most important is the type of carbohydrate you choose to eat because some sources are healthier than others.
The amount of carbohydrate in the diet – high or low – is less important than the type of carbohydrate in the diet. For example, healthy, whole grains and whole wheat bread, rye and barley are better choices than highly refined white bread or french fries.
Foods high in carbohydrates are an important part of a healthy diet. Carbohydrates provide the body with glucose, which is converted to energy used to support bodily functions and physical activity. But carbohydrate quality is important; some types of carbohydrate-rich foods are better than others:
· The healthiest sources of carbohydrates—unprocessed or minimally processed whole grains, vegetables, fruits and beans— promote good health by providing vitamins, minerals, fiber, and a host of important phytonutrients.
· Unhealthier sources of carbohydrates include white bread, pastries, sodas, and other highly processed or refined foods. These items contain easily digested carbohydrates that may contribute to weight gain, interfere with weight loss and promote diabetes and heart disease.