Chapter 4 Carbohydrates: Sugar, Starch, Glycogen, and Fiber

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.


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.


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.


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


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


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


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


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


Nutrition Carbohydrate timing

Evenly spaced Sugar alcohols

Advantages Artificial sweeteners Weight control


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


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


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

Documents

Chapter 4 Carbohydrates: Sugar, Starch, Glycogen, and Fiber