Dietary fiber is a substance contained in plant food that cannot be decomposed by human digestive enzymes. Although it cannot be absorbed by the body, it is a necessary substance to maintain human health, and is collectively known as dietary fiber in nutrition. Dietary fiber can be classified according to solubility: 1. water-soluble dietary fiber: mainly refers to the storage material and secretion of plant cells, microbial polysaccharides and synthetic polysaccharides. 2. non-water-soluble dietary fiber: mainly refers to cellulose, hemicellulose and lignin, which are components of plant cell walls and are widely found in the outer skin of cereal and legume seeds and the stems and leaves of plants, and have the property of absorbing water. Dietary fiber has a variety of physicochemical properties and physiological functions, and plays a very important role in maintaining the health of the body. The main functions are: 1, improve gastrointestinal function: water-soluble vitamins can produce short-chain fatty acids after fermentation by colonic bacteria, thus providing seventy percent of the energy required by the colonic mucosa, and can mediate nerve function, balance hormone levels, stimulate the secretion of digestive enzymes, etc. In addition, it can also directly dilate blood vessels to promote blood circulation in the colon. 2, balance intestinal flora: normal flora in the intestinal tract depend on each other, mutual Constraint. Soluble dietary fiber can provide an ideal breeding ground for intestinal flora, so that the number of intestinal bacteria can be increased, but when the intestinal bacteria multiply excessively, dietary fiber can accelerate their discharge by promoting intestinal peristalsis, thus maintaining the dynamic balance of intestinal bacteria. In addition, dietary fiber is also involved in maintaining the integrity of the intestinal mucosa, can prevent intestinal bacteria through the intestinal wall to the intestine to move outside the disease, thus effectively protecting the human body. 3, to prevent constipation, reduce plasma cholesterol: the causes of constipation is very complex, except for gastrointestinal diseases, a significant part of which is caused by poor living habits, the lack of essential dietary fiber in the diet is one of the important reasons. Dietary fiber in food absorbs water in the intestine and swells fully, making the volume of stool increase and become soft, and can stimulate the intestinal wall, thus promoting the effective peristalsis of the intestinal wall, so that the stool in the large intestine to shorten the residence time, so that the intestinal contents quickly through the intestine and out of the body, reducing the contact time between the toxins produced by harmful bacteria in the stool or harmful metabolites and the intestinal wall, in addition, the dietary fiber in food can also In addition, dietary fiber in food can also absorb bile acids, increasing their content in the stool, so that the bile salts recovered through the liver and intestinal cycle is reduced, the liver needs to use more cholesterol to synthesize new bile acids, so increase the content of dietary fiber in food can not only prevent constipation, but also reduce the level of plasma cholesterol. 4, remove toxins from the body, eliminate body waste: a variety of enzymes produced by bacteria in the intestine can break down food residues, producing some Toxic substances, which is a normal physiological phenomenon, but if long-term constipation can make a large number of toxic substances in the body for a long time, thus producing adverse effects on the human body, certain symptoms, such as bitter mouth, bad breath, nausea, abdominal pain, bloating and other discomfort. Dietary fiber can adsorb, dilute and wrap various toxins, and at the same time promote the rapid discharge of toxic substances out of the body.5. Prevent colorectal cancer: Some carcinogens are often produced in the human intestine, some are endogenous, such as nitrite produced by bacteria in the colon, bile acid metabolism produces stone bile acid, etc.; some are exogenous, entering the body with drinking and eating, such as heterocyclic compounds produced by baking or frying food. If carcinogenic substances accumulate in the intestine for a long time, it will greatly increase the chance of causing cancer. Non-soluble dietary fiber can absorb water, dilute carcinogenic substances, soften stools in the intestine, promote intestinal peristalsis and speed up defecation, thus reducing the chance of carcinogenic substances coming into contact with the intestinal wall, thus effectively preventing the occurrence of colorectal cancer. On the one hand, dietary fiber is beneficial to human health, but on the other hand, if too much is consumed, it will affect the absorption of vitamins and trace elements, so nutritionists have stipulated the daily intake of dietary fiber. Nutritionists around the world have different standards for the daily intake of dietary fiber, the U.S. Food and Drug Administration (FDA) recommends 25-35g per person per day; British nutritionists recommend 25-30g per person per day; the reference intake of dietary nutrients for Chinese residents issued by the Chinese Nutrition Society in 2000 is 30.2g per person per day. For children and adolescents between the ages of 2 and 18, due to the needs of growth and development, the demand for dietary fiber is relatively less, and the appropriate intake is age plus 5 g. Experts from the Nutrition Society believe that this is conducive to keeping their bowels open and helps prevent hyperlipidemia and cardiovascular diseases.