Transcript Chapter One
Carbohydrates Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings What Are Carbohydrates? Carbohydrates • One of the three macronutrients • A primary energy source, especially for nerve • • cells Composed of carbon, hydrogen, oxygen Good sources include fruits and vegetables Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings What Are Carbohydrates? Glucose • The most abundant carbohydrate • Produced by plants through photosynthesis Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Photosynthesis Visuals unlimited 6 CO2(gas) + 12 H2O(liquid) + photons→ C6H12O6(aqueous) + 6 O2(gas) + 6 H2O(liquid) Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings What Are Carbohydrates? Simple carbohydrates • Contain one or two molecules • Monosaccharides contain only one molecule • Glucose, fructose, galactose • Disaccharides contain two molecules • Lactose, maltose, sucrose Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Monosaccharides Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Disaccharides Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings What Are Carbohydrates? Complex carbohydrates • Long chains of glucose molecules • Hundreds to thousands of molecules long • Also called polysaccharides • Starch, glycogen, most fibers Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Complex Carbohydrates Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Complex Carbohydrates Starch • Plants store carbohydrates such as starch • We break down starch to glucose • Grains, legumes, and tubers are good sources of starch in our diet germ endosperm bran Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Amylopectin Whole Grains Bran= Roughage endosperm germ Fiber B-vitamins Trace minerals Phytochemicals Endosperm= Energy Carbohydrates Protein bran Germ= Nutrients Ex: wheat, barley, oat grains Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings B-vitamins Vitamin E Trace Minerals Phytochemicals Unsaturated lipids Complex Carbohydrates Glycogen • Animals store carbohydrates as glycogen • Stored in the liver and muscles • Not found in food and therefore not a source of dietary carbohydrate Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Complex Carbohydrates Fiber • Dietary fiber is the non-digestible part of plants • Grains, rice, seeds, legumes, fruits • Functional fiber is carbohydrate extracted from plants and added to food • Cellulose, guar gum, pectin, psyllium • Total fiber = dietary + functional fiber Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Digestion of Carbohydrates Salivary amylase • Enzyme that begins carbohydrate digestion in the • mouth Breaks carbohydrates down to maltose There is no digestion of carbohydrates in the stomach. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Digestion of Carbohydrates Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Digestion of Carbohydrates Most chemical digestion of carbohydrates occurs in the small intestine. Pancreatic amylase • Enzyme produced in the pancreas and secreted • into the small intestine Digests carbohydrates to maltose Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Digestion of Carbohydrates Additional enzymes in the small intestine digest disaccharides to monosaccharides: (1) maltase (2) sucrase (3) lactase Monosaccharides are absorbed into the cells lining the small intestine and then enter the bloodstream. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Digestion of Carbohydrates All monosaccharides are converted to glucose by the liver. Glucose circulating in the blood is our primary energy source. Excess glucose is converted to glycogen by the liver. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Storage of Glycogen Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Digestion of Carbohydrates We do not have the enzymes necessary to digest fiber. Bacteria in the large intestine can break down some fiber. For humans, most fiber remains undigested and is eliminated with feces. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Regulation of Blood Glucose The level of glucose in the blood must be closely regulated. Two hormones, insulin and glucagon, control the level of glucose in the blood. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Regulation of Blood Glucose: Insulin Insulin • Produced by beta cells of the pancreas • Helps cells take in glucose from the blood • Stimulates the liver to take up glucose and convert it to glycogen Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Regulation of Blood Glucose: Insulin Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Regulation of Blood Glucose: Glucagon Glucagon • Produced by alpha cells of the pancreas • Stimulates the breakdown of glycogen to • glucose to make glucose available to cells of the body Stimulates gluconeogenesis – the production of glucose from amino acids Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Regulation of Blood Glucose: Glucagon Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Regulation of Blood Glucose Glycemic index • A food’s ability to raise blood glucose levels • Foods with a low glycemic index: • Are better for people with diabetes • Are generally higher in fiber • May reduce the risk of heart disease and colon cancer Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Glycemic index Classification GI range Examples Low GI 55 or less Medium GI 56-69 Most fruit and veggies (not potato), basmati rice, oats, allbran Sucrose, Mars bar High GI 70 or more Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Corn flakes, baked potato, jasmine rice, white bread, white rice The Role of Carbohydrates Energy • Each gram of carbohydrate = 4 kcal • Red blood cells rely only on glucose for their • • energy supply Both carbohydrates and fats supply energy for daily activities Glucose is especially important for energy during exercise Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings The Role of Carbohydrates Energy • Sufficient energy from carbohydrates prevents • • production of ketones as an alternate energy source Excessive ketones can result in high blood acidity and ketoacidosis High blood acidity damages body tissues Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings The Role of Carbohydrates Energy • Insufficient carbohydrate intake causes the • body to find an alternate source of glucose Often proteins are used for gluconeogenesis – the production of new glucose Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings The Role of Carbohydrates Fiber • May reduce the risk of colon cancer • May reduce the risk of heart disease • May enhance weight loss • Help prevents hemorrhoids, constipation, and diverticulosis Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings How Much Carbohydrate? Recommended Dietary Allowance (RDA) is 130 grams/day just to supply the brain with glucose. 45-65% of daily calorie intake should be in the form of carbohydrates. Focus on foods high in fiber and low in added sugars. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Simple vs. Complex Carbs Diets high in simple sugars: • Can cause dental problems such as cavities and • • gum disease Are associated with increased levels of “bad cholesterol” Are associated with decreased levels of “good cholesterol” Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Simple vs. Complex Carbs The Adequate Intake (AI) of fiber is 14 grams for every 1,000 kcal in the diet. Most Americans eat only half the recommended amounts of fiber. Whole grain foods are a more healthful choice than foods with added sugar. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Alternative Sweeteners Nutritive sweeteners • Contain 4 kcal energy per gram • Sucrose, fructose, honey, brown sugar, sugar alcohols Non-nutritive (alternative) sweeteners • Provide little or no energy Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Alternative Sweeteners Acceptable Daily Intakes (ADI) have been established for: aspartame sucralose acesulfame-K No ADI has been set for saccharin but it has been removed from the list of cancer-causing agents. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Alternative Sweeteners Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Health Disorders Three health disorders related to carbohydrate metabolism are • Diabetes • Hypoglycemia • Lactose intolerance Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Diabetes Diabetes • Inability to regulate blood glucose levels • Three types: • Type 1 diabetes • Type 2 diabetes • Gestational diabetes • Untreated diabetes can cause nerve damage, kidney damage, blindness, and can be fatal Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Diabetes Type 1 diabetes • Accounts for 10% of all cases • Patients do not produce enough insulin • Causes hyperglycemia – high blood sugar • • (glucose) Requires insulin injections May be an autoimmune disease Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Diabetes Type 2 diabetes • Most diabetics have Type 2 diabetes • Body cells are insensitive or unresponsive to • • insulin Excess insulin is often produced Causes hyperglycemia because cells cannot take in the glucose from the blood Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Diabetes Type 2 diabetes • Cause is unclear but genetics, obesity, and • • physical inactivity play a role Treated with diet, exercise, and possibly oral medications Healthy lifestyle choices may prevent or delay onset of type 2 diabetes Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Hypoglycemia Hypoglycemia • Low blood sugar (glucose) • Reactive hypoglycemia results when too much insulin is produced after a meal • Causes shakiness, sweating, anxiety • Fasting hypoglycemia results when too much insulin is produced even when the patient has not eaten Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Lactose Intolerance Lactose intolerance • Insufficient lactase production causes an • • inability to digest lactose found in dairy products Symptoms include intestinal gas, bloating, nausea, cramping, diarrhea Lactose intolerant people may need to find alternate sources of calcium Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Why are carbs so important? Brain cells require two times as much energy as other cells in your body! A lack of glucose affects your ability to think and remember. Neurons from entorhinal cortex (Limbic System) ©1998 Dr. Norberto Cysne Coimbra M.Sc., Ph.D., Laboratory of Neuroanatomy and Neuropsychobiology, Faculty of Medicine of Ribeirão Preto of the University of são Paulo; Neuroscience Art Galleries Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings