Absorption of Dietary Carbohydrates

The main sites of breakdown of dietary carbohydrates are the mouth and the duodenum. 

The process starts in the mouth during mastication where salivary a-amy-lase cleaves some of the a-1,4 glycosidic bonds of starch. 

This process is completed in the duodenum where pancreatic a-amylase produces a mixture of monosaccharides, disaccharides, and oligosaccharides. 

Disaccharides are cleaved to monosaccharides by a battery of disaccharidases after absorption into intestinal mucosal cells. 

Uptake of monosaccharides and disaccharides by intestinal mucosal cells is mediated by a variety of transporters. 

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Which of the following drugs is taken during the first part of a meal for the purpose of delaying the absorption of dietary carbohydrates ... 

More extensive reviews describing antiobesity drugs which function by modulating energy intake, intestinal absorption of dietary carbohydrate or lipid, fatty acid synthesis, lipid utilization and energy expenditure have appeared recently. ... 

Dietary fiber Can slow absorption of refined carbohydrates and lower glycemic index of foods, resulting in reduced effects of diabetes due to lower availability of glucose Preuss (2009)... 

Amine and Hegsted (1971) obtained similar carbohydrate effects studying iron absorption. Glucose is the most commonly used source of dietary carbohydrate in semipurified diets. Pennell et al. (1976) reported that beta-lactose in place of sucrose reduced the relative biological value of iron as sodium iron pyrophosphate when fed to rats. However, alpha-lactose or glucose in place of the sucrose did not affect the bioavailability of this iron source. Similarly, the source of fat can affect the bioavailability of dietary iron but, the level of dietary fat has no effect (Mahoney et al., 1980). 

Glycosidase inhibitors (Table 1.9) delay the digestion of dietary carbohydrate in the form of starch and sucrose into monosaccharides, which can be absorbed from the small intestine. By delaying absorption, these agents lower postprandial blood glucose and insulin levels and are used for this purpose in the treatment of type 2 diabetes. 

Fructose is found in many plants and is an important portion of dietary carbohydrate. Most commonly it is ingested as free fructose or sucrose. Fructose is not actively transported by the intestinal mucosa, and variable proportions are converted to glucose in the process of absorption in man, about one-sixth is converted (Ml). Most of the metabolism of fructose occurs in the liver. If a renal threshold for fructose exists, it is very low. 

Inhibition of Carbohydrate Absorption - The concept that retardation of the digestion of dietary carbohydrates would lead to a diminished postprandial glycemia, insulinemia and triglyceridemia in patients with diabetes and/or obesity has stimulated the development of a number of inhibitors. Dietary di-, oligo- and polysaccharides must be degraded to monosaccharides by intestinal glucosidases before they are absorbed. 

It has been reported that the absorption of dietary procyanidins may be influenced by the matrix within which these compounds are consumed [62], Ortega et al. [30] and Serra et al. [32] studied the in vitro bioavailability of procyanidins in two cocoa matrices with different fat content and in a sample matrix that contained a carbohydrate-rich food, respectively, using a UHPLC-MS/MS method. 

Another possible mechanism for the effect of dietary carbohydrates on cholesterol metabolism is that the carbohydrates affect the absorption of cholesterol. Dietary fructose with cholate gave rise to a hypercholesterolemia in rats, cornstarch was not very effective in this regard, and sucrose and dextrose were intermediate (Portman et al., 1956b). Sucrose favors cholesterol reabsorption in chicks when compared with glucose (Grant and Fahrenbach, 1957) and in rabbits lactose gives rise to more reabsorption than sucrose (Wells and Anderson, 1959). 

Dietary carbohydrates may affect the absorption of dietary fat and thus influence the lipemia that follows a fat meal which in turn will alter lipid metabolism. It has been shown that giving carbohydrate with a fat meal decreased the subsequent lipemia (Albrink et al, 1958)... 

Thus the alpha and the omega of dietary carbohydrate and its eifect on lipid metabolism are to some extent known. The intermediate stages are obscure and would involve consideration of the metabolic role of fructose, the physical and biochemical aspects of absorption, the influence of dietary carbohydrates on gut microflora and in tmn their effect on lipid metabolism, and the possibility that metabolic pathways show some adaptation to dietary carbohydrates. The lipid responses to dietary carbohydrates reflect differences in the type of carbohydrate eaten, in the sex and age of the individual eating it, in the amount consumed, and in the nature of the accompanying dietary lipid. There are many variables and the disclosure of the intermediate stages of the dietary carbohydrate Lipid interrelationships will therefore need careful and precise study. 

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