Lecture 3 Ch. 5 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. 104 Suns energy + water + CO2 -----> O2 + carbohydrate Process of Photosynthesis simple sugar produced is metabolized to more complex forms for storage Carbon, Hydrogen and Oxygen sugars, starches and dietary fiber

Mono and Di Saccharides Mono - one ; Di - two glucose - major form, all converted to glucose for use in our bodies (glucose-glucose) is maltose (glucose-fructose) is sucrose fructose - fruit sugar galactose - combined with glucose is lactose, milk products

Complex Carbohydrates Starches and dietary fiber (polysaccharides) highly recommended forms of food intake starches - digestible polysacch. amylose - straight chains of glucose (veg., bread, pasta, rice, beans…) storage in plants Glycogen - branched glucose more chains, increases breakdown animal storage in liver (blood glucose) and muscle (movement)

Dietary Fiber Insight p. 111-115 Indigestible polysaccharides. Insoluble fibers - cellulose, hemicellulose, lignin structural part of plants do not dissolve in water Soluble Fibers - 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, see table 3-4 p. 114 MODERATION

Carbohydrate Digestion Begins with cooking salivary amylase (enzyme) mixes with food, begins break down of starch stops in stomach due to acid pancreatic amylase (enzyme) released into small intestine to breakdown to monosaccharides Sucrase, Maltase, Lactase (enzyme) 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 red blood cells and brain, glucose is 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 into body via portal vein hyperglycemia - too high released in urine, diabetes hypoglycemia - too low irritable, headache, hungry Mainly controlled by hormones from the pancreas and adrenal glands

Blood Glucose Pancreatic hormones (fig. 4-8) 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

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 Multifaceted Control System

Recommendations No RDA, minimum 50 - 100 g 55 % of total calories reduce fat, increase fiber sugar intake below 10 % average ~ 16 % only a problem if nutrient rich food is ignored in favour of sweet foods MODERATION

Sweeteners Nutritive Alternatives Sucrose high fructose corn syrup sugar alcohol - sorbitol, mannitol, xylitol, 3 kcal /g Saccharin - (1879) link with cancer, no ban Aspartame - (1981) amino acids and methanol, 200 times sweeter than sucrose damaged by cooking PKU (phenylketonuria)

Sweeteners Alternatives Sucralose -(1998) WHY? Acesulfame-K - (1988) no energy value can be cooked Sucralose -(1998) excreted, not used for energy WHY? Diabetics, calories, dental