I. Definition Since the components included in dietary fiber are very complex, and the detection methods used have not been standardized so far, its exact definition has not been determined, and its general definition is as follows. Dietary fiber is mainly polysaccharides that cannot be used by the human body, i.e. polysaccharides that cannot be digested by digestive enzymes in the human gastrointestinal tract and are not absorbed and used by the human body. These polysaccharides are mainly complex carbohydrates from plant cell walls and can also be called non-starch polysaccharides, i.e. non-alpha-glucan polysaccharides. In recent years, it has also been suggested that unavailable oligosaccharides or resistant oligosaccharides (RES). They are also included in the composition of dietary fiber. Before 1970, there was no term “dietary fiber” in nutrition, but only “crude fiber”. Crude fiber was once considered a non-nutritional component that had no nutritional effect on the body. Nutritionists considered that eating too much crude fiber would affect the absorption of nutrients in food, especially micronutrients. However, through research and investigation in the past 20 years, it has been found and recognized that this “non-nutrient” is closely related to human health and plays an important role in preventing certain diseases in the human body, and it has also been recognized that the concept of “crude fiber” is no longer applicable, so the term “crude fiber” has been replaced by “crude fiber”. The term “crude fiber” was abandoned and replaced by “dietary fiber”. Dietary fiber is a type of carbohydrate that cannot be digested by the body and can be divided into two basic types: water-soluble fiber and non-water-soluble fiber. Cellulose, hemicellulose and lignin are three common types of insoluble fiber, which are found in plant cell walls, while pectin and gum are water-soluble fibers, which are found in non-fibrous substances in nature. Common foods such as barley, beans, carrots, citrus, flax, oats and oat bran are rich in soluble fiber. Soluble fiber can slow down digestion and excrete cholesterol most quickly, so it can keep blood sugar and cholesterol under control at the most ideal level, and can also help diabetics lower insulin and triglycerides. Insoluble fiber includes cellulose, lignin and some semi-fiber as well as wheat bran, corn bran, celery, fruit peel and root vegetables from food. Third, the main characteristics 1, water absorption. Dietary fiber has a strong ability to absorb water or the ability to combine with water. This effect can make the volume of stool in the intestine increase, speed up its transit speed, reduce the time of harmful substances in contact with the intestinal wall. 2.Sticky effect. Some dietary fibers have strong viscosity and can form mucus-type solutions, including pectin, gum, algal polysaccharides, etc. 3, binding organic compounds role. Dietary fiber has the role of binding bile acid and cholesterol. 4.Cation exchange effect. Its role is related to the carboxyl group of glyoxylate, which can bind inorganic salts in the gastrointestinal tract, such as potassium, sodium, iron and other cations to form dietary fiber complexes, affecting its absorption. 5, the role of bacterial fermentation. Dietary fiber is easily fermented by bacteria in the intestine, of which soluble fiber can be completely fermented by bacteria, while insoluble dietary fiber is not easily fermented. The short-chain fatty acids produced after fermentation, such as ethyl ester acid, propyl ester acid and butyl ester acid, can be used as a source of energy for intestinal cells and bacteria. It promotes intestinal motility, reduces flatulence and improves constipation.