Dietary fiber is defined as a kind of non-starch polysaccharide and lignin that can not be digested and absorbed by digestive enzymes in human intestine, but can be partially decomposed and utilized by some microorganisms in large intestine. Structurally, dietary fiber is mainly composed of the following parts: cellulose, hemicellulose, pectin, gum, lignin, resistant starch and so on.

Second, the classification of dietary fiber

Soluble dietary fiber (SDF): It includes hydrocolloid substances, such as gelatin and part of hemicellulose. Gum, pectin, alginate, bean gum, agar, carboxymethyl cellulose, etc.

B) Insoluble dietary fiber (IDF): including cellulose, lignin and part of hemicellulose. Cellulose, hemicellulose, lignin, pectin and a small amount of gum. Composition of plant cell wall

Third, dietary fiber and nutrition

Although the research on dietary fiber was carried out earlier in the field of nutrition, the previous data mainly focused on the adverse effects of this food component on the absorption of other nutrients and the damage of crude fiber to the digestive system. In recent years, the research on dietary fiber not only affirmed its health care function beneficial to human health, but also put forward the recommended intake on the basis of dietary surveys in some countries.

Before 1970, there was no word "dietary fiber" in nutrition, only "crude fiber". Crude fiber was once considered as a non-nutritional component that had no nutritional effect on human body. Nutritionists believe that excessive intake of crude fiber will affect the absorption of nutrients in food, especially trace elements. However, through nearly 20 years of investigation and study, it is found and recognized that this "non-nutrient" is closely related to human health and plays an important role in the prevention of some diseases in human body. At the same time, it is also recognized that this concept of "non-nutrition" is no longer applicable, so the word "crude fiber" was abandoned and replaced by "dietary fiber". Due to the progress of analysis and detection methods, dietary fiber can be divided into two categories: one is soluble and the other is insoluble, and the sum of them is total dietary fiber. These two types of dietary fiber play a preventive and health care role in some chronic non-communicable diseases of human body. Therefore, it can also be said that "dietary fiber" is a "functional component" with health care function in food.