Dietary liber

American Dietetic Association. 2002. Health implications of dietary liber. JADA 102 994—1000. 

Terminology. Dietary fiber is the accepted terminology in the United States for nutritional labeling. Total dietary liber (TDF) and its subtractions, insoluble dietary fiber (IDF) and soluble dietary fiber (SDF). are defined analytically by official methods. 

Any starch escaping digestion in the upper gastrointestinal tract also contributes to dietary liber effects. Some food starches, and the amylosc... 

Most of prebiotics are nondigestible oligosaccharides they are obtained by extraction from plants (e.g., inulin from chicory), possibly followed by enzymatic hydrolysis (e.g., oligofructose from inulin), or by synthesis from mono or disaccharides. Among all the prebiotics, innlin, and oligosaccharides are certainly the most studied and have been recognized as dietary libers in the world. The most important prebiotics are presented in Table 37.2. 

Alginate is a non-digestible polysaccharide and can be classified as dietary liber. Dietary alginate can produce an improvement in the gastro-intestinal barrier function and a reduction in the damaging potential of the luminal contents with changes in the colonic microflora. On the other hand, dietary alginate reduces intestinal nutrient absorption and promotes satiety both of which have implications for the control of Type II diabetes and obesity [91]. 

The by-products of the milling system are bran, shorts (inseparable mixture of bran endosperm and germ that remains after flour extraction), germ, and red-dog flour (a low-grade flour consisting of endosperm and bran taken from the tail of the mill). Due to its high dietary liber content and relatively low amounts of lipids, wheat bran is preferred over other somces of dietary fiber for the production of many prepared foods (Table 7.4). 

Mammals can add additional double bonds to unsaturated fatty acids in their diets. Their ability to make arachidonic acid from linoleic acid is one example (Figure 25.15). This fatty acid is the precursor for prostaglandins and other biologically active derivatives such as leukotrienes. Synthesis involves formation of a linoleoyl ester of CoA from dietary linoleic acid, followed by introduction of a double bond at the 6-position. The triply unsaturated product is then elongated (by malonyl-CoA with a decarboxylation step) to yield a 20-carbon fatty acid with double bonds at the 8-, 11-, and 14-positions. A second desaturation reaction at the 5-position followed by an acyl-CoA synthetase reaction (Chapter 24) liberates the product, a 20-carbon fatty acid with double bonds at the 5-, 8-, IT, and ITpositions. 

Dietary fats, libers, and other carotenoids have been reported to interfere with carotenoid bioaccessibility. It is clear that by their presence in the gut, lipids create an environment in favor of hydrophobic compounds such as carotenoids. When arriving in the small intestinal lumen, dietary fats stimulate bile flow from the gallbladder and therefore enhance the micelle formation, which in turn could facilitate the emulsification of carotenoids into lipid micelles. Without micelle formation, carotenoids are poorly absorbed a minimum of 3 g of fat in meal is necessary for an efficient absorption of carotenoids, except for lutein esters that require higher amounts of fat. ... 

Lipoprotein metabolism. Entero-cytes release absorbed lipids in the form of triglyceride-rich chylomicrons. Bypassing the liver, these enter the circulation mainly via the lymph and are hydrolyzed by extrahepatic endothelial lipoprotein lipases to liberate fatty acids. The remnant particles move on into liver cells and supply these with cholesterol of dietary origin. 

Bi2 are only about 2 meg, it would take about 5 years for all of the stored vitamin B12 to be exhausted and for megaloblastic anemia to develop if Bi2 absorption were stopped. Vitamin B12 in physiologic amounts is absorbed only after it complexes with intrinsic factor, a glycoprotein secreted by the parietal cells of the gastric mucosa. Intrinsic factor combines with the vitamin Bi2 that is liberated from dietary sources in the stomach and duodenum, and the intrinsic factor-vitamin Bi2 complex is subsequently absorbed in the distal ileum by a highly selective receptor-mediated transport system. Vitamin Bi2 deficiency in humans most often results from malabsorption of vitamin B12 due either to lack of intrinsic factor or to loss or malfunction of the specific absorptive mechanism in the distal ileum. Nutritional deficiency is rare but may be seen in strict vegetarians after many years without meat, eggs, or dairy products. 

The overwhelming majority of foods contain amino acids, either in the free form (e.g., fruit juice) or in the form of protein (partially hydrolyzed or intact). Proteins are polymers, and their monomeric units are amino acids. Predominantly, proteins are comprised of 20 amino acids (see Fig. 1). In addition, some structural proteins contain large amounts of hydroxyproline (e.g., collagen). Far less abundant is the amino acid hydroxy lysine. The principal sources of dietary amino acids for humans are proteins, which are enzymatically digested to liberate their constituent amino acids. 

A number of animal studies have shown that dietary fibers, which liberate a constant and elevated supply of butyrate to the colon, are the most effective for prevention of chemically induced colon tumors. Moreover, the level of butyric acid in the colonic lumen of patients with colorectal cancer and adenomas was found to be lower than that in healthy individuals (Parodi, 2004). 

In the diet, vitamin B12 is bound to proteins. Although some release of protein-bound vitamin B12 begins in the mouth, most of the release occurs in the stomach on exposure of food to gastric acid (HC1) and the proteolytic enzyme pepsin. For this reason, either hypo-chlorhydria (abnormally low concentration of HC1 in gastric fluid) or achlorhydria (the absence of HC1 in gastric fluid) may decrease the availability of dietary vitamin B12 for absorption by preventing the activation of pepsinogen to pepsin, the principal enzyme responsible for proteolysis in the stomach. Achlorhydric patients with adequate production of IF may have low normal or subnormal serum B12 concentrations because of failure to liberate B12 bound to food. 

Poultry. More than 100 papers have been published on the value of supplementing diets of farm animals with L-ascorbic acid. The overall results are at times controversial. Enhancement of poultry growth has been reported by several workers using purified (144,145) and practical (146,147,148) rations and not by others (149), the general interpretation being that the ascorbic acid does not function directly but indirectly, involving a protective action or improved utilization of other nutrients. Added dietary ascorbic acid has been reported to stimulate synthesis or liberation of folic acid by intestinal bacteria, to aid in its conversion to folacin (146,150,151,152), to reinforce antibiotics in high... 

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