Carbohydrate digestion and absorption

Effect of a Glucose-Lysine Reaction Mixture on Protein and Carbohydrate Digestion and Absorption... 

Hannan, J.M., Ali, L., Rokeya, B., Khaleque, J., Akhter, M., Flatt, P.R. and Abdel-Wahab, Y.H. (2007) Soluble dietary fibre fraction of Trigonella foenum-graecum (fenugreek) seed improves glucose homeostasis in animal models of type 1 and type 2 diabetes by delaying carbohydrate digestion and absorption, and enhancing insulin action. British Journal of Nutrition 97(3), 51 4-521. 

Unfortunately, the gastric contents were exposed to regurgitated duodenal contents, and the fluid collected from the pyloric fistulas was exposed to pancreatic juice. Therefore, London s data, presented in immense tables, cannot be used to determine carbohydrate digestion and absorption in the stomach in the absence of pancreatic juice. When he cast the balance between the carbohydrate he had fed and the carbohydrate he recovered from the pyloric fistulas, he found that for the dog with the fistula closest to the pylorus 0.02% of the carbohydrate was missing. For the other two dogs with fistulas farther from the pylorus, London found that 2.77 and 18.78% were missing. On the basis of these data, London said emphatically that there is no absorption, gar keine Resorption, of carbohydrate in the stomach. 

Digestion and absorption in the small intestine. Most digestion and absorption of carbohydrates, proteins, and lipids occurs in the small intestine. A summary of the digestive enzymes involved in these processes is found in Table 18.3. 

The digestion and absorption of fat is considerably more complex than that of carbohydrate or protein because it is insoluble in water, whereas almost aU enzymes catalyse reactions in an aqueous medium. In such media, fat can form small droplets, an emulsion, which is stable in this medium. Formation of an emulsion is aided by the presence of detergents these possess hydrophobic and hydrophilic groups, so that they associate with both the fat and the aqueous phases. Such compounds are known as emulsifying agents and those involved in digestion are mainly the bile salts and phospholipids. 

These agents are administered to aid in the digestion of food. The primary digestant preparations contain pancreatic enzymes or bile salts. Pancreatic enzymes such as amylase, trypsin, and lipase are responsible for digestion of carbohydrates, proteins, and lipids, respectively. These enzymes are normally synthesized in the pancreas and secreted into the duodenum via the pancreatic duct. Bile salts are synthesized in the liver, stored in the gallbladder, and released into the duodenum via the common bile duct. Bile salts serve to emulsify lipids in the intestinal tract and are important in lipid digestion and absorption. 

Malabsorption is defined as an inadequate assimilation of dietary substances due to defects in digestion, absorption or transport. Malabsorption can affect macronutrients (proteins, carbohydrates, fats), micronutrients (vitamins, minerals) or both, causing excessive faecal excretion and producing nutritional deficiencies and GI symptoms. Digestion and absorption occur in three phases, namely (i) the intra-lumen hydrolysis of fats, proteins and carbohydrates by enzymes, and emulsification by bile salts, (ii) digestion by brush-border enzymes and uptake of end-products and (iii) lymphatic transport of nutrients. Malabsorption can occur when any of these phases is impaired. 

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