chapter 4 carbohydrates: sugar, starch, glycogen, and fiber
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Chapter 4 Carbohydrates: Sugar, Starch, Glycogen, and Fiber. Nutrition : Concepts & Controversies, 12e Sizer/Whitney. Learning Objectives. Describe the major types of carbohydrates, and identify their food sources. - PowerPoint PPT PresentationTRANSCRIPT
Chapter 4 Chapter 4
Carbohydrates: Sugar, Starch, Carbohydrates: Sugar, Starch, Glycogen, and FiberGlycogen, and Fiber
Nutrition: Concepts & Controversies, 12e Nutrition: Concepts & Controversies, 12e Sizer/WhitneySizer/Whitney
Learning ObjectivesLearning Objectives
Describe the major types of carbohydrates, and identify their food sources.
Describe the various roles of carbohydrates in the body, and explain why avoiding dietary carbohydrates may be ill-advised.
Summarize how fiber differs from other carbohydrates and how fiber may contribute to health.
Learning ObjectivesLearning Objectives
Explain how complex carbohydrates are broken down in the digestive tract and absorbed into the body.
Describe how hormones control blood glucose concentrations during fasting and feasting.
Explain the term glycemic index and how it may relate to diet planning.
Learning ObjectivesLearning Objectives
Describe the scope of the U.S. diabetes problem and educate someone about the long- and short-term effects of untreated diabetes and prediabetes.
Name components of a lifestyle plan to effectively control blood glucose and describe the characteristics of a diet that can assist in managing type 2 diabetes.
Learning ObjectivesLearning Objectives
Compare the symptoms of postprandial hypoglycemia with those of fasting hypoglycemia, and name some diseases associated with the latter type.
Discuss current research regarding the relationships among dietary carbohydrates, obesity, diabetes, and other ills.
Carbohydrates Carbohydrates
Ideal nutrients Energy needs Feed brain and nervous system Keep digestive system fit Keep your body lean
Digestible and indigestible carbohydrates Complex vs. simple carbohydrates
A Close Look at CarbohydratesA Close Look at Carbohydrates
Contain the sun’s radiant energy Green plants
Photosynthesis Glucose
Plants do not use all of the energy stored in their sugars
Carbohydrate-rich foods Plants Milk
Carbohydrate – Mainly Glucose – Carbohydrate – Mainly Glucose – Is Made by Photosynthesis Is Made by Photosynthesis
Sun
Energy
Carbon dioxide
ChlorophyllGlucose
Oxygen
WaterFig. 4.1, p. 108
Energy
A Close Look at Carbohydrates - A Close Look at Carbohydrates - SugarsSugars
Six sugar molecules Monosaccharides
Glucose, fructose, galactose Disaccharides
Lactose, maltose, and sucrose Digestion of mono- and disaccharides
Chemical names end in -ose
How Monosaccharides Join to How Monosaccharides Join to Form Disaccharides Form Disaccharides
Fructose Glucose Galactosea
Sucrose Maltose Lactoseb
(fructose-glucose) (glucose-glucose) (glucose-galactose)
aGalactose does not occur in foods singly but only as part of lactose.
Three types of monosaccharides…
…join together to make three types of disaccharides.
bThe chemical bond that joins the monosaccharides of lactose differs from those of other sugars and makes lactose hard for some people to digest—lactose intolerance (see later section). Fig. 4.2, p. 109
A note on the glucose symbol:The glucose molecule is really a ring of 5Carbons and 1 oxygen plus a carbon “flag.”
CarbonsOxygen
For convenience, glucose is symbolized as
or
Fig. 4.2, p. 109
A Close Look at Carbohydrates – A Close Look at Carbohydrates – Starch Starch
Polysaccharides Starch
Plant’s storage form of glucose Glycogen Fiber
Nutrition For a plant For a human
How Glucose Molecules Join to How Glucose Molecules Join to Form PolysaccharidesForm Polysaccharides
Glucose
Starch (unbranched) Starch (branched) Glycogen Cellulose
Starch Glucose units are linked in long, occasionally branched chains to make starch. Human digestive enzymes can digest these bonds, retrieving glucose. Real glucose units are so tiny that you can’t see them, even with the highest-power light microscope.
Glycogen Glycogen resembles starch in that the bonds between its glucose units can be broken by human enzymes, but the chains of glycogen are more highly branched.
Cellulose (fiber) The bonds that link glucose units together in cellulose are different from the bonds in starch or glycogen. Human enzymes cannot digest them.
Fig. 4.3, p. 110
A Close Look at Carbohydrates – A Close Look at Carbohydrates – Glycogen Glycogen
Storage form of glucose Animal bodies
Chains are longer than starch More highly branched
Undetectable in meats
A Close Look at Carbohydrates - A Close Look at Carbohydrates - FibersFibers
Human digestive enzymes cannot break bonds Bacteria in large
intestineFermentation
Soluble vs. insoluble fibers
The Need for CarbohydratesThe Need for Carbohydrates
Critical energy source Nerve cells and brain
Preferred dietary sources Starchy whole foods
Complex carbohydrates
Vital roles in the functioning body
The Need for CarbohydratesThe Need for Carbohydrates
Weight loss Caloric contribution
Conversion into fat storageRefined sugars
Increase fiber-rich whole foods Reduce refined white flour and added
sugars
Why Do Nutrition Experts Why Do Nutrition Experts Recommend Fiber-Rich Foods?Recommend Fiber-Rich Foods?
Health benefits Reduced risk of heart disease Reduced risk of hypertension Reduced risk of diabetes Reduced risk of bowel disease Promotion of healthy body weight
Sources of fiber
Characteristics, Sources, and Characteristics, Sources, and Health Effects of FibersHealth Effects of Fibers
Fiber Composition of Common Fiber Composition of Common FoodsFoods
Why Do Nutrition Experts Why Do Nutrition Experts Recommend Fiber-Rich Foods?Recommend Fiber-Rich Foods?
Lower cholesterol and heart disease risk Complex carbohydrates
More than just fiber Viscous fiber
Cholesterol synthesis
Blood glucose control Whole grains
Soluble fibers
One Way Fiber in Food May One Way Fiber in Food May Lower Cholesterol in the BloodLower Cholesterol in the Blood
Gallbladder stores bile
Liver uses blood cholesterol to
make bileIntestine: bile aids digestion; binds to fiber
Fiber and bile excreted in
feces
A little cholesterol in bile reabsorbed
into the blood
A. High-fiber diet
1.2.
3.
4.
5.
Fig. 4.6a, p. 116
Gallbladder stores bile
Liver uses blood cholesterol to
make bileIntestine: bile aids digestion
Little bile excreted
Much of the cholesterol in bile absorbed into the
blood
B. Low-fiber diet
1. 2.
3.
4.
5.
Fig. 4.6b, p. 116
Why Do Nutrition Experts Why Do Nutrition Experts Recommend Fiber-Rich Foods?Recommend Fiber-Rich Foods?
Maintenance of digestive tract health All kinds of fiber Ample fluid intake Benefits of fiber
Constipation, hemorrhoids, appendicitis, diverticulosis
DiverticulaDiverticula
Diverticula
Colon
Fig. 4.7, p. 117
Fig. 4.7, p. 117
Diverticulum
Why Do Nutrition Experts Why Do Nutrition Experts Recommend Fiber-Rich Foods?Recommend Fiber-Rich Foods?
Digestive tract cancer and inflammation Ways fiber works against cancer
DilutionFolateResident bacteriaButyrate
Recommended dietary sources Healthy weight management
Appetite control
Fiber Recommendations and Fiber Recommendations and IntakesIntakes
Few people in U.S. meet recommendations 20-35 grams of fiber daily
Based on energy needs, age, and gender Adding fiber to diet
Too much fiber? Dangers of excess
Binders in fiber Chelating agents Cause of deficiencies
Usefulness of CarbohydratesUsefulness of Carbohydrates
Refined, Enriched, and Whole-Refined, Enriched, and Whole-Grain FoodsGrain Foods
Bread supplies much carbohydrate for many people
Kernel (whole grain) has four main parts Germ Endosperm Bran Husk
A Wheat Plant and a Single A Wheat Plant and a Single Kernel of WheatKernel of Wheat
Headbeard
kernels
Stem
Root
A wheat plant
A kernel of wheat
husk (chaff)
bran (14%)
endosperm (83%)
germ (2.5%)
Fig. 4.8, p. 120
Refined, Enriched, and Whole-Refined, Enriched, and Whole-Grain FoodsGrain Foods
U.S. Enrichment Act of 1942 Required additives
Addition in 1996 Advantages of
whole grains vs. enriched grains
Finding the whole grains in foods
Nutrients in Whole-Grain, Enriched Nutrients in Whole-Grain, Enriched White, and Unenriched White BreadsWhite, and Unenriched White Breads
Bread Labels ComparedBread Labels Compared
From Carbohydrates to Glucose – From Carbohydrates to Glucose – Digestion & AbsorptionDigestion & Absorption
Starch and disaccharides are broken down Monosaccharides for absorption
Starch Begins in the mouth
Splits starch into maltose Digestion ceases in the stomach Digestion resumes in small intestine
Pancreas Resistant starch
From Carbohydrates to Glucose – From Carbohydrates to Glucose – Digestion & AbsorptionDigestion & Absorption
Sugars Split to yield free monosaccharides
Enzymes on small intestine lining Travel to the liver
Fiber Fermented by bacteria in the colon
Odorous gas Gradually increase fiber intakes
How Carbohydrate in Food How Carbohydrate in Food Becomes Glucose in the BodyBecomes Glucose in the Body
Fig. 4.11, p. 124
Fiber and resistant starch travel unchanged to the colon.
Fiber, starch, monosaccharides, and disaccharides enter the stomach and pass into the small intestine. Some of the starch is partially broken down by an enzyme from the salivary glands before it reaches the small intestine.
The liver can convert galactose and fructose to glucose.
Monosaccharides enter capillaries, and are then delivered to the liver via the portal vein.
Enzymes on the surface of cells that line the intestine split disaccharides to monosaccharides.
An enzyme from the pancreas digests most of the starch to disaccharides.
Intestinal wall cells
Large intestine (colon)
Stomach
Pancreas
Esophagus
Liver
lactose sucrose maltose
Key:
Small intestine
galactose
Capillary
fiberstarch
1 2
3
4
56
1
2
3
4
5
6
Why Do Some People Have Why Do Some People Have Trouble Digesting Milk?Trouble Digesting Milk?
Ability to digest milk carbohydrates varies Lactase
Made by small intestine
Symptoms of intolerance Nausea, pain, diarrhea, and gas
Milk allergy Nutritional consequences Milk tolerance and strategies
The Body’s Use of GlucoseThe Body’s Use of Glucose
Basic carbohydrate unit used for energy Body handles glucose judiciously
Maintains an internal supply Tightly controlling blood glucose
concentrations Brain, nervous system, red blood cells
Splitting Glucose for EnergySplitting Glucose for Energy
Glucose is broken in half Can reassemble Broken into
smaller molecules IrreversibleTwo pathways
Carbon atomsBonds
Glucose(6-carbon compound)
3-carbon compound
2-carbon compound
Carbon dioxide
2 molecules of carbon dioxide
Fig. 4.12, p. 126
Splitting Glucose for EnergySplitting Glucose for Energy
Glucose can be converted to fat Fat cannot be converted to glucose Dependence on protein when insufficient
carbohydrateProtein-sparing action
Ketosis Shift in body’s metabolism
Disruption of acid-base balance
DRI minimum of digestible carbohydrate
How Is Glucose Regulated in the How Is Glucose Regulated in the Body?Body?
Two safeguard activities Siphoning off excess blood glucose Replenishing diminished glucose
Two hormones Insulin
Signals body tissues to take up glucose Glucagon
Triggers breakdown of glycogen
Epinephrine
Handling Excess GlucoseHandling Excess Glucose
Body tissue shift Burn more glucose
Fat is left to circulate and be stored
Carbohydrate storage as fat Liver breakdown and assembly Costs a lot of energy
Weight maintenance Dietary importance and composition
Glycemic Index of FoodGlycemic Index of Food
Elevation of blood glucose and insulin Food score compared to standard food
Diabetes Glycemic load (GL)
Lower GL = less glucose guild up and less insulin needed
Limitations of glycemic index Resist notion of “good” or “bad” foods
Glycemic Index of Selected FoodsGlycemic Index of Selected Foods
Fig. 4.13, p. 129LOW
Fructose
Peanuts
Soybeans
Cashews, cherriesBarleyKidney beansChickpeas (garbanzo beans)Butter beans, lentilsSoy milkYogurt, milkTomato juice, navy beans, apples, pearsApple juice, dates, carrotsBran cereals, black-eyed peas, peaches, orangesChocolate pudding, chocolate candyGrapes, corn tortillasGreen peas, baked beans, pastaRye bread, orange juiceBananas, mangoesCorn, pound cakeOatmeal, cookedIce creamCola, pineappleHoneyCouscous, sucrose (table sugar)Raisins, brown rice
White bread, wheat bread, white ricePumpkin, popcorn, bagelWatermelon, doughnutSports drinks, jelly beansOatmeal, instantBaked potato, boiled potatoCornflakesRice milkMashed potato, instant; rice crackers
GlucoseHIGH
12
0
25
37
50
62
75
87
100
DiabetesDiabetes
Prevalence of diabetes Adults Children
Prediabetes Importance of testing
Perils of diabetes Toxic effects of excess glucose Inflammation Circulation problems
Prevalence of Diabetes Among Prevalence of Diabetes Among Adults in the United StatesAdults in the United States
Fig. 4.14, p. 130
1997: Ten states had a prevalence of diabetes of less than 4% and only five states had a prevalence of 6% or greater.
4%–5.9%
<4% 8%–9.9%≥10%
6%–7.9%
Key:
Fig. 4.14, p. 130
2007: No state had a prevalence of diabetes of less than 4%; all but three states had a prevalence of 6% or greater, with eight states reporting a prevalence of 10% or greater.
4%–5.9%<4% 8%–9.9%
≥10%6%–7.9%
4%–5.9%<4% 8%–9.9%
≥10%6%–7.9%
Key:
Warning Signs of DiabetesWarning Signs of Diabetes
Type 1 DiabetesType 1 Diabetes
5 to 10 percent of cases Common age of occurrence Autoimmune disorder
Own immune system attacks pancreas Lose ability to produce insulin
External sources of insulin Fast-acting and long-acting forms
Type 2 DiabetesType 2 Diabetes
Predominant type of diabetes Lose sensitivity to insulin Obesity underlies many cases Other factors foreshadowing development
Middle age and physical inactivity Body fat accumulation Genetic inheritance
Prevention
Type 1 and 2 Diabetes ComparedType 1 and 2 Diabetes Compared
An Obesity-Diabetes CycleAn Obesity-Diabetes Cycle
• Genetic inheritance• Excess food energy• Inadequate physical activity
• Obesity
• Reduced glucose use for fuel• Increased fat stores
• Enlarged fat mass• Elevated blood lipids• Inflammation
• Type 2 diabetes• Hormone imbalance
• Insulin resistance
Fig. 4.15, p. 132
Management of DiabetesManagement of Diabetes
Controlling blood glucose is key Monitoring blood glucose levels Taking medications
Control body fatness Establish good eating patterns
Management of DiabetesManagement of Diabetes
Nutrition Goal: blood glucose levels in normal range Control carbohydrate intake
Amount rather than source seems to matter Carbohydrate recommendations
Varies with glucose tolerance Exchange system
Management of DiabetesManagement of Diabetes
Nutrition Carbohydrate timing
Evenly spaced Sugar alcohols
Advantages Artificial sweeteners Weight control
Management of DiabetesManagement of Diabetes
Physical activity Benefits of regular
activity Type 2 diabetes
vs. type 1 diabetes
HypoglycemiaHypoglycemia
Rare, but true disease Abnormally low blood glucose
Postprandial hypoglycemia Requires test to detect
Fasting hypoglycemia Symptoms
Methods to reduce symptoms
Finding Carbohydrates in FoodsFinding Carbohydrates in Foods
Fruits Vary in water, fiber, & sugar concentrations
Juice
Vegetables Breads, grains, cereals, rice, & pasta
Brown color does not equal whole grain Low-fat and low-sugar choices
Finding Carbohydrates in FoodsFinding Carbohydrates in Foods
Meat, poultry, fish, dry beans, eggs, & nuts Nuts and legumes
Milk, cheese, & yogurt High-quality protein
Oils, solid fats, & added sugars Naturally occurring vs. added sugars Honey
Finding Carbohydrates in FoodsFinding Carbohydrates in Foods
The nature of sugar Teaspoon values High-fructose corn syrup Concentrated juice sweeteners Ways to magnify sweetness without calories
Are Carbohydrates “Bad” for Are Carbohydrates “Bad” for HealthHealth
Controversy 4
Accusation 1: Carbohydrates Are Accusation 1: Carbohydrates Are Making Us FatMaking Us Fat
Americans are fatter Greater
consumption of calories300-500 per day
Epidemiological studies
Weight loss
Percentage of Calories from Energy Percentage of Calories from Energy Nutrients, U.S., 1977-2006Nutrients, U.S., 1977-2006
Daily Energy Intake Over TimeDaily Energy Intake Over Time
Accusation 2: Carbohydrates Accusation 2: Carbohydrates Cause DiabetesCause Diabetes
Obesity and diabetes Refined carbohydrates and diabetes
Native Americans Glycemic load and diabetes
Whole foods
Accusation 3: Added Sugars Accusation 3: Added Sugars Cause Obesity and IllnessCause Obesity and Illness
Current trends Daily Per year
Relationship with disease
Added Sugars: Average U.S. Supply per Added Sugars: Average U.S. Supply per Person Compared with USDA Prudent Person Compared with USDA Prudent
Upper Intake LimitsUpper Intake Limits
Accusation 4: High-Fructose Corn Accusation 4: High-Fructose Corn Syrup Harms HealthSyrup Harms Health
Villainy has been exaggerated Nature of HFCS
Half of added sugar in U.S. food supply Obesity
HCFS not a proven cause Liquid sugar and calorie control Appetite regulation
Fructose does not stimulate insulin release
Accusation 4: High-Fructose Corn Accusation 4: High-Fructose Corn Syrup Harms HealthSyrup Harms Health
Effects on lipid metabolism Fructose causes
fats to accumulate in blood and liver
Metabolic activities of concern
Accusation 5: Blood Insulin Is To Accusation 5: Blood Insulin Is To BlameBlame
Presence of insulin Body tends to store energy
Claims made about insulin Expert standing on insulin
Insulin does not cause accumulation of excess body fat