The traditional definition of Dietary Fiber is a substance that can be found in plant cell wall and cells but cannot be dissolved by our digestive enzymes. Though containing the same carbohydrate composition as amylum, dietary fiber can not be digested and absorbed by our body because of its different linking, and will eventually be egested. In consequence, it was regarded previously as useless substance. Fibers in food, in general, can be divided into two groups: Insoluble Dietary Fiber (IDF) and Soluble Dietary Fiber (SDF); and the combination of these two is commonly known as Total Dietary Fiber (TDF).
IDF, known as Crude Fiber in Traditional Nutrients Table, includes:
The biggest difference between IDF and SDF lies in the water-holding capacity. SDF possesses a better capacity to hold water for the formation of normal excrements to be easily egested; therefore, SDF is more helpful for constipation improvement.
In fact, recent nutrition studies reveal that, dietary fiber performs various functionalities in keeping our physical functions well and in disease control. Those functionalities include:
Besides, it is also helpful for maintaining intestinal bacteria balance, preventing malignant bacteria. Researches indicate that, dietary fiber provides a vigorous growth of intestinal lactobacillus.The increase of probiotics with the decrease of malignant bacteria will definitely keep our body healthy. It can be therefore regarded as one prebiotics. Promoting the secretion of intestinal mucus that protects parietal cells from the invasion of harmful obstacles, it delays the absorption of polysaccharides, ease up the rise of blood sugar, reduce the secretion of insulin, and helps controlling and preventing diabetes.
To sum up, the advantages of dietary fiber are:
Excess intake of dietary fiber, however, may result in some side effects, including:
American Dietetic Association (ADA) addresses the positive effects of dietary fiber on health, suggesting the public to intake enough amount dietary fiber from different vegetables and fruits. The suggested daily intake amount is 20 -35 grams for an adult and 25-40 grams for the children according to their age.
The original definition of dietary fiber in the past was made only based on physical functions and analysis methods while it actually allows a much wider range for food components. And with the rapid development of modern technologies and food industry, lots of food components similar to dietary fiber, such as resistant starch, oligosaccharide and inulin, are not included in the definition of dietary fiber. The confinement in the old definition of dietary fiber is becoming clearer. Furthermore, people’s awareness of its important physical functions brings out a plenty of dietary fiber foods. Eventually, American Association of Cereal Chemists (AACC) set up a committee specific for the definition of dietary fiber in 1998. And on June 23rd, 1999, AACC and the International Life Sciences Institute (ILSI) together established an enforcing committee. What is more, a specific seminar for the definition of dietary fiber was held in the annual meeting of the Institute of Food Technologists (IFT) in Chicago on July 26th, 1999, and the same year, a discuss was made in the 84th AACC annual meeting with a final definition of dietary fiber concluded as followed:
Dietary fiber is a vegetable component for diet that cannot be absorbed by small intestines in human body, but can be fermented partly or completely by large intestines. It is a combination of carbohydrate and other similar substances, including polysaccharides, oligosaccharides, Lignin, and related vegetable substances. Dietary fiber provides one and more physical functions, like constipation releasing, blood sugar control, and the decrease of blood fat.
The above description explicitly defines dietary fiber as a edible vegetation composition but not organic composition. And its main components are: celluloses, hemicelluloses, pectin; soluble colloids, like gums and algae polysaccharides; lignin in plant cell wall; indigestible substances, like resistant starch, resistant dextrin, modified celluloses, mucilage, oligosaccharides; and a few related components, like waxes, cutin, and suberin.
Chitin and chitosan are organic aminopolysaccharides, while some scholars insist that they should be defined as dietary fiber because of their special structures. Similar to the fiber, both are constructed with straight chain polymer, a composition of 1000 – 3000 n- Acetyl -d –Glucosamine morphons in a B-1,4 chain. Straight chain polymer is a natural and digestible polymer without toxicity, so as to be regarded as the organic polymer with most potential. In the nature, chitin is the most common aminopolysaccharide next to fiber, and can be generally found on the shell of invertebrates like insects and aquatic crustacean, and also on the cell wall of fungus. Its main functions in organics are to support body structure as skeletons and to provide protection. Chitosa is the product after the deacetylation of chitin. As a rule, a merely 70 % completion of the deacetylation on chitin can turns it into chitosa, soluble in acid.
Introduction on Dietary Fiber
September 29, 2008 by simonbwidjanarko