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Carbohydrates

Carbohydrates. Zeina Ghossoub El-Aswad, MSc. CHO. Basic fuel source: Energy is a necessity for life. It is the power an organism requires to do its work. In the human energy system, this major basic fuel comes from CHO foods we eat. This is especially the case of the nervous system.

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Carbohydrates

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  1. Carbohydrates Zeina Ghossoub El-Aswad, MSc

  2. CHO • Basic fuel source:Energy is a necessity for life. It is the power an organism requires to do its work. • In the human energy system, this major basic fuel comes from CHO foods we eat. This is especially the case of the nervous system.

  3. Energy Production System • CHO are changed into glucose. • The body then absorbs it and through blood circulation, carries this refined fuel to the cells that need the glucose. • Glucose is burned in the cells, releasing energy through cell metabolism. CHO are called “quick energy” foods because of their rapid metabolism • Plants manufacture and store CHO as their chief source of Energy through Photosynthesis.

  4. Practical Dietary Importance • a-CHO are widely available, low in cost and easily grown as compared to many other food items. • b-CHO may be easily stored. They can be kept in dry storage for a long period of time

  5. CLASSIFICATION OF CHOs • -CHO are organic molecules composed of carbon (C), hydrogen(H) and oxygen(O), with the ratio of 1:2:1. • -CHOs are classified according to their complexity (the number of sugar units making up their structure), their solubility and their food sources

  6. Simple CHOs • Basic units of polysaccharides. • A-Glucose: • -Sometimes known as dextrose • -Basic simple sugar in body metabolism • -Supplier of the primary fuel for cells in the body. • -Present in fruits, sweet corn, corn syrup, honey and certain roots. • -Most of the body supply of glucose should come from the digestion of starch

  7. Simple CHOs • B-Fructose: • -Found mainly in fruits and honey. • -It is the sweetest of the simple sugars. • C-Galactose: • -Not usually found in the diet but comes from the digestion of the milk sugar lactose

  8. Simple CHOs • These monosaccharides require no digestion. They are absorbed in the body from the intestine to the bloodstream and carried to the liver and other tissues. There they are converted to glycogen or used for immediate energy needs

  9. Disaccharides • They are made of 2 single sugar units (monosaccharides) linked together. • A-Sucrose: • -Common table sugar • -Sucrose=glucose+fructose • -Sources are: sugar beets, sugar cane, molasses

  10. Disaccharides • B-Maltose: • -Not usually found as such in the diet • -Derived from the breakdown of starch in the body • -Maltose=glucose+glucose • C-Lactose: • -Main milk sugar • -Not found in plants • -It is less soluble and less sweet than sucrose and it stays longer in the intestine • -It is formed in mammary glands • -Lactose=glucose+galactose

  11. Complex CHOs • These are composed of many sugar units. They include starch, glycogen and dietary fibers. • A-Starch: • -Found only in plants: grains, legumes and other vegetables • -Complex CHO that breakdown more slowly than simple sugars and supplies more energy over a longer period of time

  12. Complex CHOs • B-Glycogen: • -Similar in structure to starch and is the form of storage of CHO in humans and animals. • -Found in liver and muscles where it is constantly being recycled to form glucose for immediate energy needs and resynthesized for liver and muscle storage. • -These glycogen stores help providing fuel for periods of fasting (sleep) and provides immediate fuel for muscle action

  13. Complex CHOs • C-Dietary fibers: • These are polysaccharides but they have no nutrient value because the human body lacks the necessary enzymes to digest them. This inability to be digested makes them important dietary factors. • *Cellulose: -Provides important bulk to the diet but no energy. • -Main sources are fruits, vegetables, stems, leaves of vegetables, covering of seeds and grains(whole grains, skins)

  14. Complex CHOs • *Non-Cellulose Polysaccharides: • -Such as:Hemicellulose, pectins, gums and mucilages. • -They absorb water and swell to a larger bulk • -They slow the emptying of the food mass from the stomach, bind to bile acids including cholesterol and provide bulk for normal muscle action

  15. CLASSIFICATION ACCORDING TO DIGESTIBILITY • *Digestible fibers: Starch,dextrin,glycogen • -Starch can be : readily digestedwhite rice, white bread • slowly digestedlegumes, vegetables • resistant-----potatoes, bananas • *Indigestible Fibers: Cellulose, hemicellulose, pectin, gums and mucilages

  16. CLASSIFICATION ACCORDING TO SOLUBILITY IN WATER • *Insoluble in water: cellulose, lignin and most hemicelluloses • *Soluble in water: Gums, mucilages and most pectins

  17. HEALTH BENEFITS OF FIBERS • -Weight control • -Constipation (shortening transit time) • -Colon cancer • -Cardiovascular diseases • -Diabetes • **Excess intake of fibers is not very appreciated as they bind minerals and vitamins. RDA is 30g/day.

  18. FUNCTIONS OF CHOs • -Major energy source • -Integrity of nerve tissues • -Components of cell structure • -Precursor of organic compounds (nucleic acids) • -Protein sparing • -Prevents ketosis

  19. FOOD SOURCES OF CHOs • Mainly in 4 food groups: grains, vegetables, fruits and milk • -In breads, grains and starchy vegetables: • 1portion=1/2 cup of starchy vegetables=60kcal from starch • 1portion=1 slice of bread=60kcal from starch=15g CHO • 1 portion=1/2 cup of non starchy vegetables=20kcals from starch

  20. FOOD SOURCES OF CHOs • -In fruits: • 1 portion=15 g CHO=60Kcal from CHO • -In milk and milk products: 1 portion=1cup of milk=12gCHO=50kcal from CHO

  21. RDA FOR CHO • The RDA for CHO is 55-60% of total Kcal • Food intake from CHO should be mainly of starch with a minimal intake of simple sugars.

  22. DIGESTION AND ABSORPTION • I- Digestion of CHO begins in the mouth to progress through the successive parts of the gastrointestinal tract. This process is accomplished by 2 types of action: • Mechanical or muscle functions that break the food mass into smaller particle • Chemical processes in which specific enzymes breakdown the food nutrients into smaller usable metabolic products.

  23. DIGESTION AND ABSORPTION • A-In the mouth: • The salivary enzyme Ptyalin breaks down starch into dextrin and maltose • B-In the stomach: • Contraction of the muscle fibers of the stomach walls continues the mechanical digestive process. This action is called Peristalsis. It further mixes the food particles with the gastric secretions that allow chemical digestion to take place more easily

  24. DIGESTION AND ABSORPTION • -Action of salivary Ptyalin is stopped by the HCl in the stomach • -Muscle action continues to mix the food mass and move it to the lower part of the stomach forming a chyme that moves to the duodenum. • C-In the small intestine: • -Peristalsis continues to help digestion in the small intestine by mixing and moving the chyme along the length of the tube

  25. DIGESTION AND ABSORPTION • -Chemical digestion of CHO is completed by specific enzymes from both the pancreas and the intestine. • Pancreas: Secretions from pancreas enter through the pancreatic bile duct. They contain a starch-pancreatic amylase that continues the breakdown of starch to maltose.

  26. DIGESTION AND ABSORPTION • Intestine: Secretions contain 3 disaccharidases:sucrase, lactase, maltase. These act on their respective disaccharides to yield monosaccharides absorbed directly in the portal blood circulation.

  27. DIGESTION AND ABSORPTION • Absorption of CHO occurs primarily in the Small Intestine. It can occur by diffusion or by active transport. • From the blood stream, the digested CHOs are transported to any part of the body where they are used or stored in the liver as glycogen. In the case of excess intake, they are stored as triglycerides in adipose tissues. • Fructose and galactose are transformed to glucose.

  28. How Food Carbohydrate Becomes Body Glucose (Slide 1 of 4) 1. Fiber, starch, mono- saccharides, and disaccharides enter the small intestine. (some of the starch is partially broken down by an enzyme from the salivary glands before it reaches the small intestine.) (See next slide)

  29. How Food Carbohydrate Becomes Body Glucose (Slide 2 of 4) 2. An enzyme from the pancreas digests the starch to disaccharides. 3. Enzymes on surface of intestinal wall cells split disaccharides to monosaccharides. 4. Monosaccharides enter capillary, then are delivered to liver via the portal vein. (See next slide)

  30. How Carbohydrate Becomes Body Glucose (Slide 3 of 4) 5. Liver converts galactose and fructose to glucose.

  31. How Carbohydrate Becomes Body Glucose (Slide 4 of 4) 5. Fiber travels unchanged to the colon.

  32. REGULATION OF BLOOD SUGAR • Normal blood sugar level is 70-100mg/dl under fasting conditions. This level is maintained by metabolic and hormonal control. • Recent recommendations to discuss 90 mg/dl as a cut off point

  33. REGULATION OF BLOOD SUGAR • Metabolic control:blood sugar levels are regulated by several ways; one is hormonal • Liver glycogen is constantly converted to glucose and diffused in blood to be taken up by tissues by a process called glycogenolysis. Muscle glycogen is used for energy only by the muscle and cannot be returned to the blood glucose

  34. REGULATION OF BLOOD SUGAR • When adequate glucose is not available such as in fasting or prolonged high level energy expenditure, amino acids are converted to glucose through the process of gluconeogenesis

  35. REGULATION OF BLOOD SUGAR • Insulin: • -Major hormone. • -Secreted by the islets of Langerhans in the pancreas. • -It is liberated upon a high blood glucose level. • -Also stimulated by glucagon and gastrointestinal hormone. • -Increases the rate of glucose utilization.

  36. REGULATION OF BLOOD SUGAR • Increases diffusion of glucose into muscle and adipocytes (lipogenesis). • -Increase storage of glycogen in liver and muscles • Decrease blood glucose levels by favoring its storage and utilization by the cells

  37. REGULATION OF BLOOD SUGAR • Glucagon: • -Opposite effect to insulin. • -Produced by the pancreas • -Causes a rise in blood sugar by increasing blood glucose levels especially between meals glycogen breakdown • -Stimulates the release of insulin by the pancreas

  38. REGULATION OF BLOOD SUGAR • Epinephrine: • Produced by adrenal medulla. • Favors the breakdown of liver and muscle glycogen to yield blood glucose. • Decreases the secretion of insulin from the pancreas, thus raises blood sugar levels. • Its secretion is favored by anger and fear. • Increases blood glucose levels and its utilization by the cells ( fight or flight response)

  39. HEALTH PROBLEMS ASSOCIATED WITH EXCESS SUGAR INTAKE • 1-Dental Caries: • These are infectious oral diseases that develop in tooth enamel. They develop when the bacteria digest the CHO producing acids that attack the enamel. • People with more than 10% of Kcal from sugar are at risk of developing dental caries. • Recommendations to avoid caries would be; • Watch for hidden sugars • Restrict sweets • Brush after meals or rinse with water • Eat a balanced diet • Eat a diet high in fibers

  40. HEALTH PROBLEMS ASSOCIATED WITH EXCESS SUGAR INTAKE • 2-Empty Calories of sugar: • -Sugar intake must be moderate (5-10% of total Kcal) • -Comparison of honey vs. table sugar

  41. MEDICAL CONDITIONS ASSOCIATED WITH ABNORMAL CHO METABOLISM • 1-Diabetes Mellitus: • A metabolic disorder characterized by high blood sugar or glucose and either insufficient or ineffective insulin. • Insulin dependant diabetes mellitus(IDDM) occurs mainly in childhood and is characterized by lack of insulin synthesis. It needs treatment by insulin injections. • Non-insulin dependant diabetes mellitus(NIDDM)occurs in adulthood and is characterized by ineffective insulin production. It is aggravated by obesity and high body fat

  42. MEDICAL CONDITIONS ASSOCIATED WITH ABNORMAL CHO METABOLISM • 2-Lactose intolerance: • A disorder characterized by the deficiency of the digestive enzyme lactase that splits the lactose disaccharide into galactose and glucose • Symptoms are cramps, abdominal distension and diarrhea due to gases and undigested sugars.Foods to avoid would be milk, whey, milk solids and all products containing lactose

  43. The Obesity--Diabetes Cycle.

  44. Diabetes Types 1 and 2 Compared

  45. MEDICAL CONDITIONS ASSOCIATED WITH ABNORMAL CHO METABOLISM • 3-Post-Prandial hypoglycemia: • It is a sudden decrease in blood sugar level that approximates a fasting state almost instantly. It occurs almost 1 hour after a meal

  46. ALTERNATIVE SWEETENERS • Sugar alcohols:or nutritive sweeteners. • maltitol, mannitol, sorbitol and xylitol • -sweet tasting • -yield 4Kcal/g • -absorbed more slowly in the body • -Better for dental caries as they do not produce acids

  47. ALTERNATIVE SWEETENERS • 2-Artificial sweeteners: • -They are :saccharin, aspartame • -They are both virtually calorie free

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