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3. Carbohydrate (CHO) Carbohydrates are compounds made up of types of sugars. Carbohydrates are classified according to their degree of polymerization and may be divided initially into three principal groups, namely sugars, oligosaccharides and polysaccharides. They constitute a large part of foods such as rice, noodles, bread, and other grain-based products. The major dietary carbohydrates : Class Sugars (1-2) igosaccharides (3-9) Polysaccharides (>9) Sub-Group Monosaccharide Disaccharides polyose Malto-oligosaccharides Other oligosaccharides Components Fructose, galactose and glucose, lactose, sucrose and maltose . mannitol and sorbitol maltodextrins fructo-oligosaccharides, raffinose and stachyose, Starch Amylose, amylopectin, modified starches Non-starch polysaccharides Cellulose, hemicelluloses, pectin's, hydrocolloids Polysaccharides are often referred to as complex carbohydrates because they are typically long multiple branched chains of sugar units. The difference is that complex carbohydrates take longer time to digest and absorb than simple sugar, since their sugar units must be separated from the chain before absorption. The spike in blood glucose levels after ingestion of simple sugars is thought to be related to some of the heart and vascular diseases which have become more frequent in recent times. Simple sugars form a greater part of modern diets than formerly, perhaps leading to more cardiovascular disease. The major sources of carbohydrate in the human diet are: 1. Cereals . 2. Root crops . 3. Sugar crops . 4. Pulses . 5. Vegetables . 6. Fruit . 7. Milk products . The importance of Carbohydrates to health Carbohydrates have a wide range of physiological effects which may be important to health, such as: 1. sources of energy 2. Effects on satiety /gastric emptyingشبع 3. Control of blood glucose and insulin metabolism 4.Control of colonic epithelial cell function 5. Protein glycosylation 6. Cholesterol and triglyceride metabolism 7. Bile acid dehydroxylation 8. Fermentation 9. Hydrogen/methane production 10. Short-chain fatty acids production 11. Bowel habit/laxation/motor activity 12. Effects on large bowel microflora Carbohydrate as an energy source : Dietary carbohydrates have by convention been given an energy value of 4 kcal/g. Some carbohydrates are partly or not digested in the small intestine and are fermented in the large bowel to short chain fatty acids. These include :•non-digestible oligosaccharides, •starch •non-starch polysaccharides. Glucose and blood sugar level : The digestion of dietary carbohydrates starts in the mouth, where salivary amylase initiates starch degradation. The amylase degradation of starch is completed by the pancreatic amylase active in the small intestine. Dietary disaccharides, as well as degradation products of starch, need to be broken down to monosaccharides in order to be absorbed. This final hydrolysis is accomplished by hydrolases enzymes attached to the intestinal membrane brush-border, referred to as "disaccharidases". Glucose and galactose are transported actively against a concentration gradient into the intestinal mucosal cells by a sodium dependent transporter . Fructose undergoes facilitated transport by another mechanism . Fructose taken together with other sugars is better absorbed than fructose alone. The absorbed carbohydrates cause an elevation of the blood glucose concentration. Fructose and galactose have to be converted to glucose mainly in the liver and therefore produce less pronounced blood glucose elevation. The extent and duration of the blood glucose rise after a meal is dependent upon:- the rate of absorption, which in turn depends upon factors such as gastric emptying as well as the rate of hydrolysis and diffusion of hydrolyzed products in the small intestine. Fermentation : Fermentation is the colonic phase of the digestive process and describes the breakdown in the large intestine of carbohydrates not digested and absorbed in the upper gut. This process involves gut micro-flora and is unique to the colon of humans because it occurs without the availability of oxygen. It thus results in the formation of the gases hydrogen, methane and carbon dioxide, as well as short chain fatty acids (SCFA) (acetate, propionate and butyrate), and stimulates bacterial growth (biomass). The gases are either absorbed and excreted in breath, or passed out via the rectum. The major products of such fermentation are the Short Chain Fatty Acids (SCFA) which are rapidly absorbed and metabolized by the body. Micro-flora Carbohydrate which is fermented stimulates the growth of bacteria in the large gut. This is a generalized effect which leads to an increase in the total number of bacteria or biomass. When bacterial growth occurs, the micro-flora synthesize protein actively from preformed amino acids and peptides. Carbohydrates A. Monosaccharide's 1. Glucose(dextrose) : The monosaccharide glucose in the body is commonly called blood sugar. It is the major form of sugar in the blood. Normal fasting blood sugar (FBS) is 70 to 100 milligrams per 100 milliliters of serum or plasma. Impaired fasting glucose (IFG) is 100 to 125 milligrams per 100 milliliters of serum or plasma . Regardless of the form of sugar consumed, the body readily converts it to glucose 2. Fructose : Fructose is found in fruits and honey. It is the sweetest of all the monosaccharide's. Fructose is used extensively in soft drinks, canned foods, and various other processed foods .The human body readily converts fructose to glucose. 3. galactose : The monosaccharide galactose comes mainly from the breakdown of the milk sugar lactose. Yogurt and unaged cheese may contain free galactose. It is the least sweet of all the monosaccharide's. The body converts galactose into glucose after ingestion. B. Disaccharides : 1. Maltose = (glucose + glucose) The disaccharide maltose is produced when the body breaks starches into simpler units. Smaller amounts of this disaccharide are present in malt, malt products, beer, some infant formulas, and sprouting seeds. 2. Sucrose = (glucose + fructose) : The most prevalent disaccharide, sucrose, is ordinary white table sugar made commercially from sugar beets and sugar cane. Brown, granulated, and powdered sugars are all forms of sucrose. Sucrose is also found in molasses, maple syrup, fruits, and vegetables 3. Lactose = (glucose + galactose) Because lactose occurs naturally only in milk, it is commonly referred to as milk sugar. Lactose is the least sweet of the disaccharides At birth, lactase activity is high in the brush-border of the small bowel of infants, but declines after weaning and low activity in adult life. Lactose intolerance, the term used to describe the clinical symptoms of abdominal discomfort, flatulence and diarrhea, associated with the ingestion of lactose containing foods by persons with low lactase activity. Or in injured intestinal mucosa following acute infection in children and in protein-energy malnutrition. It is also found in adults, particularly in association with celiac disease. C. Polysaccharides : A. Digestible fibers 1. starch : Starch is used as a storage polysach in plants, it founds in the form of both amylose & the branched amylopectin. Starch found in large quantities in cereals grains, potatoes, plantains. Starch, the major source of carbohydrate in the diet, is found primarily in grains, starchy vegetables, and legumes and in foods made from grains — cereals, breads, and pasta., 2. Glycogen : Glycogen represents the body’s carbohydrate stores. glucose is stored in liver and muscle tissue as the polysaccharide Glycogen . B. Indigestible fibers : (plant or dietary fibers or Non-Starch Polysaccharides Fiber ) : Dietary fiber refers to foods, mostly from plants, that the human body cannot break down to digest and that is eliminated in intestinal waste. Sometimes called roughage or bulk, fiber adds almost no fuel or energy value to the diet, but it does add volume. Bulk fills the stomach, and most experts believe a full stomach contributes to a feeling of satiety, so further eating ceases. 1. Insoluble dietary fibers: (like beans, brown rice, maize, peas, breads, cereals, pasta). consist mainly cellulose & hemicelluloses. It bind to water in the colon,& stimulate peristalsis in the colon & reduce risk of constipation & ca colon. Examples of sources of insoluble fibers include the woody or structural parts of plants, such as fruit and vegetable skins, and the outer coating (bran) of wheat kernels. Insoluble fibers have been reported to promote regularity of bowel movements and reduce the risk of diverticular disease and some forms of cancer. The mechanism of these effects for insoluble fiber is due to decreased intestinal transit time and decreased intestinal pressure 2. Soluble dietary fiber (like apples, legumes, pears, strawberries). Sources of soluble fibers include beans, oatmeal, barley, broccoli, and citrus fruits; oat bran is a particularly good source of soluble fiber. Soluble fibers dissolve in water and thicken to form gels. The reported health benefits of soluble fibers include reduced cholesterol blood levels, regulated blood sugar levels, and weight loss (by helping dieters control their appetites). Soluble fiber blunts the response of blood glucose to ingestion. The reabsorption of bile acid is slowed by soluble fiber so increase cholesterol loses in feces& reduce blood cholesterol level. Dietary fiber (properties and sources) Types of dietary fiber 1. Insoluble fibers: Cellulose, some hemicelluloses, lignin . function It holds water, or it binds to water in the colon and increases fecal bulk, reduces intra-luminal pressure in the colon, stimulate peristalsis in the colon and reduce risk of constipation and CA of colon . promotes growth of helpful bacteria in the colon . source Wheat bran, bran cereals, whole grains(wheat and barley), popcorn, peanuts, apples, pears, berries, bananas, peaches, legumes, peas, cabbage family, corn, spinach, sweet potato, sunflower seeds . 1. Soluble fibers : Pectin, some hemicelluloses, gums . Binds cholesterol and bile acids(slows reabsorption of bile acids) so increases cholesterol losses in feces and reduce blood cholesterol level, slows gastric emptying, provides fermentable materials for colon bacteria with production of volatile fatty acids and gas, slows absorption of glucose, preventing rapid rise in blood glucose levels . Oat bran, oat cereals, barley, pumpernickel bread, apples, citrus fruits, pears, broccoli, Brussels, sprouts, carrots, sweet potato, white potato, peas, legumes, (gums and psyllium used as thickeners or stabilizers in processed foods) Function of dietary fibers : •Preventing and treating constipation •control of weight •Cancer prevention •Diabetes control (slows glucose absorption from intestine & decreases release of insulin). •Reduction of blood cholesterol (inhibits absorption of cholesterol and bile acids therefore it prevents CVD and obesity). Function of glucose(dextrose) : Glucose… oxidation… CO2 + H2O + 36 – 38 ATP 1. Source of energy: dietary CHO have energy value of 4 kcal/gm. number of CHO are only partly or not at all digested in the small intestine & are fermented in the large bowel to short chain fatty acids, these include the non- digestable oligosach, resistance starch & NSP. The processes of fermentation is metabolically less efficient than absorption in the small intestine &these CHO provide the body with less energy. 2. control of blood glucose & insulin metabolism: absorbed CHO cause an elevation of the blood glucose conc . Insulin is secreted as a response to blood glucose elevation. 3. protein glycosylation: the non-enzymatic glycation of proteins is dependant on the concentration of glucose in blood & the half life of the protein. 4. Preventing ketosis 5. Food palatability Glycemic Index(GI): the blood glucose response to a given food compared to a standard . Effect of high glycemic index foods on the body : 1. Increase insulin release from pancreas 2. Insulin resistance and type II DM. 3. High blood triglycerides 4. Increase fat synthesis in the liver 5. Increase fat deposition in adipose tissue. Classification of fruits according to Glycemic Index (GI) Low GI >35 Cherries (22) Grapefruit(25) Dried prunes(29) Dried apricots(30) Moderate GI 35 - 50 Apple(38) Peach, canned in juice(38) Fresh pear(38) Plum(39) Strawberries(40) Orange, navel(42) Fresh peach(42) Grapes juice(46) Fresh prunes(49) High GI <50 Banana(52) Kiwi(58) Cocktail fruit(55) Mango(51) Fresh Apricots(57) Dried figs(61) Raisins(56) Cantaloupe(65) Dates(103)