Absorption and metabolism of dietary fiber

2015-01-26 classification: efficacy effect: a large number of studies have confirmed that dietary fiber has many important physiological functions, such as preventing constipation and colon cancer, reducing blood cholesterol, stabilizing blood glucose level and reducing weight The lack of dietary fiber in human body will lead to many diseases in intestinal and cardiovascular metabolism, and enough fiber in diet will protect human body from these diseases For this reason, dietary fiber has become the "seventh largest nutrient" after protein, fat, carbohydrate, mineral, vitamin C, water, etc In Europe, the United States, Japan and other developed countries and regions have developed and produced many varieties of dietary fiber and high dietary fiber foods, which are popular with consumers However, due to the highly non-specific chemical composition of dietary fiber, not all dietary fiber has these functions The transformation from ordinary dietary fiber to high-quality dietary fiber has become the focus of research at home and abroad in recent years Dietary fiber can not be digested in human mouth, stomach and small intestine, but some microorganisms in large intestine can degrade it in different degrees The degree and speed of degradation are related to water solubility, chemical structure, particle size and intake mode of dietary fiber The type, quantity and bonding mode of monosaccharide and glucuronic acid in polysaccharide determine the degradation of the fiber in intestine to a great extent Strictly speaking, the net energy of dietary fiber is not equal to zero, but it is basically zero Water soluble cellulose, such as pectin, can be almost completely hydrolyzed, while water-insoluble cellulose, such as cellulose, is not easily affected by microorganisms The same source of dietary fiber, smaller particles are more likely to degrade than larger particles, and dietary fiber ingested alone is more likely to be degraded than contained in the food matrix Some water-soluble dietary fiber can be metabolized by some parts of the body, showing low energy value The researchers analyzed the metabolism of 14C labeled dextran in human and animals, and found that the maximum utilization rate of dextran in animals and human was 25%, its actual energy value was only 4.18kj/g, while most carbohydrate was 16.72kj/g, fat was 37.62kj/g Dextran is low energy because it is not easily absorbed by the gastrointestinal tract and is not easily degraded by microorganisms in the gut After oral intake, most of dextran (60%) is excreted in the original form into feces, while the part not excreted is utilized by intestinal microflora and can be converted into volatile fatty acids and carbon dioxide Carbon dioxide has no nutritional value, most of it is excreted as gastrointestinal gas or transported to the lungs and exhaled out of the body Volatile fatty acids are absorbed and can be used as energy sources for the body, and eventually discharged by respiration in the form of carbon dioxide In addition, dextran was found not to affect vitamins, mineral elements and essential Absorption and utilization of amino acids Dietary fiber can reduce the contact between foods in the small intestine and between foods and digestive enzymes, affecting digestion and absorption Dietary fiber can reduce the mixing of lipid and cholic acid, inhibit the emulsification of fat, and affect the absorption of lipid in the small intestine Viscous dietary fiber can delay the process of digestion and absorption by increasing the viscosity of small intestine contents, increasing the thickness of non agitated layer and other mechanisms, so that most nutrients in high fiber diet are absorbed in the lower part of small intestine Viscous dietary fiber enters the stomach with the diet, which increases the viscosity of gastric contents and delays gastric emptying, which is also one of the mechanisms of viscous polysaccharide delaying glucose absorption Usually, before most of the liquid is emptied, most of the solid substances in the diet are deposited at the bottom of the stomach, and then enter the small intestine through the antrum and pylorus When dietary mucopolysaccharides increase the viscosity of gastric contents, the prison body cannot be separated from the liquid, and the solid matter is not easy to settle in the stomach bottom, which is not conducive to gastric emptying.