THE CARBOHYDRATES: SUGARS, STARCHES, AND FIBERS CHAPTER 4

INTRODUCTION Brain  Glucose as E source Muscles  ½ Glucose & Glycogen (storage form of glucose)  ½ Fat Sources of carbohydrates “Fattening” – mistaken thinking

CHEMIST’S VIEW OF CARBOHYDRATES CHO  cmpds composed of C, O, H arranged as mono or multiple mono Dietary CHOs  Monosaccharide  Disaccharides  Polysaccharides

CHEMIST’S VIEW OF CARBOHYDRATES

Monosaccharides – three kinds  Same numbers and kinds of atoms  Differ in arrangements 1.Glucose – blood sugar 2.Fructose 3.Galactose

CHEMIST’S VIEW OF CARBOHYDRATES Disaccharides  Pairs of three monosaccharides 1.Maltose – two glucose* units 2.Sucrose – glucose* and fructose 3.Lactose – glucose* and galactose

CHO-PUT TOGETHER & TAKEN APART BY SIMILAR CHEMICAL RXNS:  Condensation (to make)  Links two monosaccharides together

CHO-PUT TOGETHER & TAKEN APART BY SIMILAR CHEMICAL RXNS: Hydrolysis (to take apart)  Breaks a disaccharide in two  Commonly occurs during digestion

CHEMIST’S VIEW OF CARBOHYDRATES Polysaccharides  Contain many glucose units  sometimes few mono strung together  Three types important in nutrition: glycogen, starch, fiber. 1.Glycogen  Storage form of energy  Many glucose units linked  Hormonal message

CHEMIST’S VIEW OF CARBOHYDRATES 2.Starch Storage form of E (glucose) in plants Long, branched, or unbranched glucose molecules Consume a plant  body hydrolyzes starch to glucose  glucose as E All come from plants (grains richest source)

CHEMIST’S VIEW OF CARBOHYDRATES 3.Fibers  Structural part in plant; found in all plant derived foods  Differ from starches  bonds between monos can’t be broken down by digestive enzymes  Soluble fibers (dissolve in water)-  form gels  easily digested  heart protective and diabetes  Insoluble fibers (do not dissolve in water)-  do not form gels  less readily fermented  promote bowel movement, aid constipation  Functional fibers  Resistant starches  Phytic acid

CARBOHYDRATE DIGESTION Ultimate goal  Glucose for absorption and use** Hydrolysis via enzymes Mouth  Salivary enzyme- amylase  starch to poly to maltose Stomach  Stomach acid & protein- inactivate amylase  No enzymes to significantly further breakdown  Role of fiber   lingers in stomach, delaying gastric emptying  fullness/satiety

CARBOHYDRATE DIGESTION Small intestine  Most carbohydrate digestion  Pancreatic amylase  major CHO digesting enzyme  Specific disaccharide enzymes  Maltase: maltose  2glucose  Sucrase: sucrose  glucose + fructose  Lactase : lactose  glucose + galactose Large intestine  Fibers only remaining  (sugars & starches digested)  Aid in healthy bowel functions/movements

CARBOHYDRATE ABSORPTION Takes place in small intestine Active transport  Glucose  Galactose Facilitated diffusion  Fructose

CARBOHYDRATE ABSORPTION

LACTOSE INTOLERANCE Lactase activity Symptoms of intolerance Causes of intolerance beyond age Prevalence

LACTOSE INTOLERANCE Dietary changes  Manage dairy consumption rather than restriction  Fermented milk products  Individualized diets  Potential nutrient deficiencies  Riboflavin, vitamin D, and calcium

CARBOHYDRATE METABOLISM Glucose is key player Storing glucose as glycogen  Liver storage  Muscle storage

CARBOHYDRATE METABOLISM Glucose for energy  Fuels most of body’s cells  Cellular breakdown of glucose into carbon dioxide and water Making glucose from protein  Amino acid conversion to glucose in some extent  Gluconeogenesis- conversion of protein to glucose (not ideal)

CARBOHYDRATE METABOLISM Ketone bodies from fat fragments  Inadequate supply of carbohydrates Carbohydrate needs for protein sparing and prevention of ketosis ( g CHO daily) Using glucose to make fat

THE CONSTANCY OF BLOOD GLUCOSE Steady supply in blood stream  Intestines – food consumption  Liver – glycogen breakdown Blood glucose homeostasis  Insulin  Glucagon & epinephrine

BLOOD GLUCOSE HOMEOSTASIS

THE CONSTANCY OF BLOOD GLUCOSE Balancing within the normal range Balanced meals at regular intervals Diabetes Blood glucose levels rises after a meal and remains above normal levels because Insulin is either inadequate or ineffective Type 1 diabetes Type 2 diabetes Hypoglycemia Blood glucose levels fall below normal Symptoms Seen in poorly managed diabetes, too much insulin, strenuous exercise, inadequate food intake, or illness

THE CONSTANCY OF BLOOD GLUCOSE Glycemic response  Speed of glucose absorption, how high level of blood glucose rises, and how quickly it returns to normal glucose levels  Important in diabetes  Low glycemic response  Desired  High glycemic response  Glycemic index-method of classifying food according to their potential to raise blood glucose

HEALTH EFFECTS OF SUGARS Pleasure in moderate amounts without harming health Nutrient deficiencies Energy with few other nutrients (empty calories) Some sugar sources are more nutritious than other Dental caries Bacteria in mouth ferment sugars producing an acid that erodes tooth enamel, causing tooth decay Practicing good oral hygiene and minimize consuming sugar and starch containing foods and beverages

RECOMMENDED INTAKES OF SUGARS Dietary Guidelines  Choose and prepare foods with little added sugar DRI  Added sugars  No more than 25% of day’s total energy WHO and FAO recommendations  Suggest restricting consumption of added sugars to less than 10% of total energy.

ALTERNATIVE SWEETENERS Artificial sweeteners  Sometimes called Non-nutritive sweeteners  Provide virtually no E  Large doses and adverse effects Stevia – an herbal product  Derives from a plant  Generally recognized as safe (GRAS)-used as additive in variety of food and drinks Sugar alcohols  Found in “sugar-free” or reduced-calorie products  Provide kcalories, but fewer than CHO sugars (nutritive sweetener)  Benefits and side effects

HEALTH EFFECTS OF STARCH AND FIBERS Heart disease  Whole grains  Soluble fibers  Sources  Bind with bile acids in GI tract  increasing excretion  Protect against heart disease and stroke

HEALTH EFFECTS OF STARCH AND FIBERS Diabetes High-fiber foods trap nutrients and delay transit time in GI tract  glucose absorption slowed GI health High-fiber foods  increase stool wt, easing passage, reduce transit time Ample fluids  easier passage Protects against colon cancer Weight management High-fiber foods and whole grains help with healthy body weight

HEALTH EFFECTS OF STARCH AND FIBERS Excessive fiber  Insufficient energy or nutrient needs  Abdominal discomfort, gas, diarrhea  GI obstruction  Nutrient absorption  Dietary goals  Balance, moderation, variety

RECOMMENDED INTAKES OF STARCH & FIBERS DRI for carbohydrates  45 to 65% of energy requirement RDA for carbohydrates  130 grams per day Fiber  DV: 11.5 grams per 1000-kcalories  DRI: 14 grams per 1000-kcalories  No UL