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Understanding Carbohydrates: Digestion, Absorption, and Dietary Sources

This guide explores the crucial role of carbohydrates in our diet, highlighting their significance as the largest source of calories, contributing 40-45% of total caloric intake. It delves into different types of dietary carbohydrates, such as starches from plants, sugars like sucrose and glucose, and dietary fibers. The digestion process is discussed, emphasizing the enzymes involved, including salivary and pancreatic amylases. Finally, the absorption of monosaccharides like glucose and galactose in the intestines is examined, providing insights into how our bodies utilize these essential macronutrients.

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Understanding Carbohydrates: Digestion, Absorption, and Dietary Sources

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  1. Digestion and absorption Carbohydrates

  2. Whenever Zachariah went into the sanctuary where she was, he found that she had food. He said: O Mary! Whence cometh unto thee this? She answered: it is from Allah. Allah gives without stint to whom he will. 37 the family of Imran Al-Qur’an

  3. Carbohydrates diet

  4. Dietary carbohydrates • Largest source of calories • 40-45% • Plant • starch ( grains, tubers, veggies )sucroseglucose fructosedietary fiber • Animal • glycogenglycolipidslactose

  5. Carbohydrates in our diet CH₂OH CH₂OH O O OH OH OH OH OH OH OH OH β-D-glucose α-D-glucose

  6. Carbohydrates in our diet CH₂OH CH₂OH O O OH OH OH OH OH OH OH OH β-D-galactose α-D-glucose

  7. Carbohydrates in our diet CH₂OH O O HOCH₂ OH OH OH OH OH CH₂OH OH OH β-D-fructose α-D-glucose

  8. Carbohydrates in our diet CH₂OH CH₂OH O O OH OH OH OH β-D-glucose α-D-glucose

  9. Carbohydrates in our diet CH₂OH O CH₂OH O OH OH OH OH β-D-galactose α-D-glucose

  10. Carbohydrates in our diet CH₂OH O O HOCH₂ OH OH OH CH₂OH OH OH β-D-fructose α-D-glucose

  11. Carbohydrates in our diet CH₂ O CH₂OH O OH OH OH OH α-D-glucose α-D-glucose

  12. Carbohydrates in our diet So what’s our relationship? O α-D-glucose O O Its called α-1—2 glycosidic bond β-D-fructose Sucrose

  13. Carbohydrates in our diet Its called β-1—4 glycosidic bond So what’s our relationship? O O O Lactose

  14. Carbohydrates in our diet Its called α-1—4 glycosidic bond So what’s our relationship? O O O Maltose

  15. Carbohydrates in our diet Of course! It’s the α-1—4 glycosidic linkages So what’s our relationship? O O O O O Maltotriose

  16. Carbohydrates in our diet So what’s our relationship? Its called α-1—6 glycosidic bond O O O Iso- maltose

  17. Carbohydrates in our diet So what’s our relationship? Its called α-1—1 glycosidic bond , is’nt it cool? O O O Trehalose

  18. Carbohydrates in our diet So what’s our relationship? Its called β-1—2 glycosidic bond O O O O O O I don’t understand! Lactulose

  19. Carbohydrates in our diet O O O O O O O We’ve got a strong relashionship, the α-1—4 glycosidic linkage Amylose

  20. Carbohydrates in our diet We are stronger, we have got α-1—4 glycosidic linkages as well α-1—6 branch points O O O O O O O O O O O Amylo-pectin

  21. Carbohydrates in our diet O O O O O O O O We are a team, we have got the β-1—4 glycosidic linkages! Cellulose

  22. Carbohydrates digestion

  23. Digestion of carbohydrates • Endoglycosidases / exoglycosidases • specific for sugar, type of bond, number of saccharide units • Glycosidases • Enzymes that hydrolyze glycosidic bonds b/w sugars

  24. Mouth • Salivary alpha amylase • Endoglycosidase • internal alpha 1,4 bonds • random intervals • No activity against • Alpha 1,6 bonds • Little or no activity against Alpha 1,4 bond at non reducing ends

  25. Salivary α-amylase O O O O O O O O O O O O O O O O O O O O O Shortened polysaccharides α-limit dextrins

  26. Stomach • Salivary alpha amylase • Inactivated by gastric HCl

  27. Small intestine • Pancreatic alpha amylase • Bicarbonate • Intestinal disaccharidases

  28. Pancreatic α-amylase • Endoglycosidase • Continues digestion of starch and glycogen • Limit dextrins • Maltotriose • Maltose • Duodenum O O O O O 4-9 glycosyl residues and 1 or more 1,6 branches O O O

  29. Intestinal disaccharidases • Glucoamylase • Sucraseisomaltase complex • Lactase glucosylceramidase/ β-glycosidase complex • Trehalase

  30. Glucoamylase • Really an oligosaccharidase • Hydrolyses 1,4 bonds of dextrins • Exoglucosidase • Begins at nonreducing end and sequentially cleaves glycosyl units • It cleaves dextrins down to isomaltose • Highest activity in ileum O O O O O O O O O O O O O O O O O O

  31. Sucrase-isomaltase complex • Sucrase-maltase • Splits sucrose, maltose and maltotriose • Isomaltase-maltase • Splits alpha 1,6 bonds in isomaltose and limit dextrins • alpha 1,4 bonds in maltose and maltotriose • Jejunum

  32. Sucrase-isomaltase complex O O O Sucrose

  33. Sucrase-isomaltase complex O O O Maltose

  34. Sucrase-isomaltase complex O O O Iso- maltose

  35. Lactase glucosylceramidase/ β-glycosidase complex • GlucosylCeramidase • Splits β-glycosidic bonds b/w glucose/galactose and hydrophobic residues • Lactase • Splits β1,4 bonds b/w glucose and galactose • Jejunum

  36. β-glycosidase complex O O O

  37. Glycolipids • Cerebrosides • Ceramide-monosaccharides • Globosides • Ceramide-oligosaccharides GLU CERAMIDE GLU GAL CERAMIDE

  38. Glycolipids • Forssman antigen • Ceramide-oligosaccharides GALNAc GALNAc GAL GAL GLU CERAMIDE

  39. Trehalase O O O Trehalose Splits α1,1 bond in trehalose Found in mushrooms,insects and seafood

  40. Carbohydrates Absorption

  41. Absorption of monosaccharides Hi! • Glucose • Fructose • Galactose • Site • Duodenum • Upper jejunum O O O

  42. Na+ O O O Na+ O O O GLUT 5 2K+ Na+ 3Na+ Na+ SGLT-1 GLUT 2 Na+ Na+ Na+

  43. Na+ O O O Na+ O O O GLUT 5 GLUT 2 Na+ Na+ SGLT-1 GLUT 2 Na+ Na+ Na+

  44. Carbohydrates Indigestible

  45. Indigestible carbohydrates • Cellulose • Hemicelluloses • Gums • Mucilages • Pectin • Raffinose • Lignin

  46. Colon • Dietary fibre and nondigested carbohydrates • Bacterial action • Gases • H2, CO2, methane • Lactate • Short chain FA • Acetic acid • Propionic acid • Butyric acid

  47. What is the cause of excessive flatulence after having a meal containing beans?

  48. Carbohydrates Disorders

  49. Abnormal degradation of disaccharides • Disorders • Lactose intolerance • Disaccharide intolerance • Isomaltasesucrase deficiency • Defect in absorption of fructose • Symptoms • Osmotic diarrhea • Bacterial fermentation • 2 and 3 carbon compounds • Gases

  50. Lactose intolerance • Etiology • Deficiency of enzyme lactase • Clinical features • Abdominal cramps • GI bloating • Intermittent diarrhea • 45min-1hr after eating dairy products

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