Lecture 3 Ch. 4 Carbohydrates

Overview Carbohydrates Sources of Carbohydrates Simple Sugars Complex Carbohydrates Dietary Fiber Digestion and Absorption Functions Blood glucose regulation Dietary sweeteners

How do we get Carbohydrates ? Figure p. 110 Process of Photosynthesis in Plants Requires the elements Carbon, Hydrogen and Oxygen Suns energy + 6water + 6CO2 -----> 6O2 + glucose (C6H12O6) simple sugar produced is metabolized to more complex forms for storage Sugars, starches and dietary fiber

Mono and Di Saccharides (simple sugars) Figure 4.1 Mono = one Glucose, galactose and fructose Di = two Sucrose, lactose and maltose glucose - major form, all others converted to glucose for use in our bodies fructose - fruit sugar galactose - combined with glucose is lactose found in milk products (glucose-glucose) is maltose (glucose-fructose) is sucrose

Complex Carbohydrates Figure 4.3 Starches and dietary fiber (polysaccharides) highly recommended forms of intake Starches - digestible polysaccharides storage form of carbs. in plants vegetables, bread, pasta, rice, beans amylose - straight chains of glucose amylopectin - branched chain starch Glycogen - branched glucose more chains, increases rate of breakdown - utilize energy faster animal storage in liver (blood glucose) and muscle (movement) Not a dietary source of carbohydrate

Dietary Fiber Indigestible polysaccharides. Fig 4.4 Insoluble fibers - whole grains, flax, veg cellulose, hemicellulose, lignin(non carb) structural part of plants do not dissolve in water Increase bulk of feces, decreases intestinal transit time Soluble Fibers - citrus fruits, oat, beans pectin, gum, mucilage inside and around plant cells dissolve or swell in water fiber rich foods are a mixture of both kinds of fiber

Dietary Fiber Retains water, increasing bulk of stool, stimulates peristalsis and facilitates elimination too little fiber, small hard stool, difficulties with elimination hemorrhoids and diverticula insoluble fibers increase stool size the most require high fluid intake may play role in preventing colon cancer

Dietary Fiber Emphasize foods rather than fiber supplements vitamin C, carotenoids, may be implicated in observed benefits soluble fiber may reduce cholesterol as it attracts bile (produced from cholesterol) and leads to its elimination in stool recommend 20-35 g per day MODERATION Table 4-6

Carbohydrates in Foods The foods that yield the highest percentages of energy from carbohydrates Table sugar, honey, jam, jelly, fruit, baked potatoes Rice bread and noodles are all high ~75% carbohydrate Peas, broccoli, oatmeal, beans, french fries and skim milk all contain moderate amounts Fig 4.5 Emphasize grains, pastas, fruits and vegetables Contain other beneficial nutrients

Sweeteners Nutritive - provide energy Sugars - all mono and disaccharides Consumption of sucrose - 12-48 pounds per person in one year in US high fructose corn syrup sugar alcohols - sorbitol, mannitol, xylitol, 1.5-3 kcal /g Alternative- provide little energy Saccharin - (1879) 300 times sweeter than sucrose Aspartame (nutrasweet/equal)- (1981) amino acids and methanol, 200 times sweeter than sucrose damaged by cooking PKU (phenylketonuria)

Sweeteners Alternatives Sucralose -(1998) WHY ALTERNATIVES? Acesulfame-K - (1988) 200x sweeter than sucrose no energy value can be cooked Sucralose -(1998) 600 times sweeter than sucrose excreted, not used for energy WHY ALTERNATIVES? Diabetics, calories, dental

Carbohydrate Digestion Figure 4-6 Begins with cooking salivary amylase (enzyme) mixes with food, begins break down of starch Digestion stops in stomach due to acidic environment pancreatic amylase (enzyme) released into small intestine to breakdown starch and small chains of glucose into maltose (disaccharide) Sucrase, Maltase, Lactase (enzymes) enzymes in wall of S I produce mono from disaccharides.

Carbohydrate Digestion Undigested disaccharide's used by bacteria in LI, produces acid and gas (abdominal discomfort) Lactose intolerance people lack sufficient lactase, usually avoid dairy can reintroduce lactose into diet slowly, small amounts are OK.

Carbohydrate Absorption Single sugars, actively absorbed by cells in wall of SI (energy) travel via portal vein to liver, to be converted into glucose used mainly for energy 4 kcal/g or stored as glycogen For red blood cells and nervous system, glucose is the only source of fuel recommend minimum 55 % of caloric intake

Functions of Carbohydrates Energy source Protein sparing effect too little carbohydrate, leads to breakdown of body protein for energy Ketosis Low carbohydrate prevents proper metabolism of fats production of ketones, altering acid/base balance and body functions sweetener

Blood Glucose Regulated very tightly liver controls entry of glucose into body Stores glucose from GI that comes via portal vein Hyperglycemia -too high-125 mg/100ml Glucose released in urine, diabetes hypoglycemia - too low - 40 mg/100ml irritable, headache, hungry Mainly controlled by hormones from the pancreas and adrenal glands

Blood Glucose Pancreatic hormones (fig. 4-7) Insulin - released with onset of eating and increase in blood glucose stimulates liver to synthesize glycogen and cells to take up glucose from the blood Glucagon - released when blood glucose drops stimulates breakdown of glycogen to glucose and its release from liver into the blood stream

Blood Glucose Adrenal Gland Epinephrine (aka adrenaline) released in response to stress increases blood glucose, promoting quick mental and physical action Balance of all these hormones is necessary to maintain blood glucose Exercise also stimulates uptake of glucose by working muscle Multifaceted Control System

Recommended Carbohydrate Intake No RDA, minimum 50 - 100 g 55 % of total calories reduce fat, increase fiber intake sugar intake below 10 % average ~ 16 % only a problem if nutrient rich food is ignored in favour of sweet foods Glycemic Index(GI) -blood glucose response in body - higher insulin release Long term may have health impact - diabetes Table 4.8 - High GI foods - baked and mashed potatoes, short grain white rice, honey, jelly beans, bagels Avoid overeating high GI and sugar Combine with lower GI foods Exercise regularly