<P> Not yet formally proposed as an essential macro-nutrient, dietary fiber is nevertheless regarded as important for the diet, with regulatory authorities in many developed countries recommending increases in fiber intake . </P> <P> Dietary fiber has distinct physicochemical properties . Most semi-solid foods, fiber and fat are a combination of gel matrices which are hydrated or collapsed with microstructural elements, globules, solutions or encapsulating walls . Fresh fruit and vegetables are cellular materials . </P> <Ul> <Li> The cells of cooked potatoes and legumes are gels filled with gelatinized starch granules . The cellular structures of fruits and vegetables are foams with a closed cell geometry filled with a gel, surrounded by cell walls which are composites with an amorphous matrix strengthened by complex carbohydrate fibers . </Li> <Li> Particle size and interfacial interactions with adjacent matrices affect the mechanical properties of food composites . </Li> <Li> Food polymers may be soluble in and / or plasticized by water . Water is the most important plasticizer, particularly in biological systems thereby changing mechanical properties . </Li> <Li> The variables include chemical structure, polymer concentration, molecular weight, degree of chain branching, the extent of ionization (for electrolytes), solution pH, ionic strength and temperature . </Li> <Li> Cross-linking of different polymers, protein and polysaccharides, either through chemical covalent bonds or cross-links through molecular entanglement or hydrogen or ionic bond cross-linking . </Li> <Li> Cooking and chewing food alters these physicochemical properties and hence absorption and movement through the stomach and along the intestine </Li> </Ul> <Li> The cells of cooked potatoes and legumes are gels filled with gelatinized starch granules . The cellular structures of fruits and vegetables are foams with a closed cell geometry filled with a gel, surrounded by cell walls which are composites with an amorphous matrix strengthened by complex carbohydrate fibers . </Li>

Where is fiber absorbed in the digestive system