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5
CARBOHYDRATES
CHAPTER OVERVIEW
Carbohydrates, the first chapter of “The Energy-yielding Nutrients” section of the text, explores
the named nutrient in detail. The structure and function of the monosaccharides, disaccharides,
oligosaccharides, and polysaccharides are discussed. Carbohydrate digestion and absorption is reviewed
for the learner, as are the common aberrations in these physiological processes. The functions of dietary
carbohydrate as a fuel, its protein sparing action, ketosis prevention, and flavor/sweetness properties are
explained. The role of fiber is also reviewed. Food sources of carbohydrate, such as sugars, starches, and
dietary fibers, are identified. Recommended carbohydrate intakes are reviewed in light of ketosis
prevention and the Dietary Guidelines. Sweeteners and several artificial sweeteners are discussed. The
chapter concludes with the Nutrition Perspective, “When Blood Glucose Regulation Fails.” This section
outlines health issues, namely diabetes and hypoglycemia, related to regulation of blood glucose levels.
CHAPTER OBJECTIVES
By the end of this chapter the student should be able to:
1.
Describe the differences and similarities among mono-, di-, oligo-, and polysaccharides and food
sources of each.
2.
Explain the functions of simple and complex carbohydrates.
3.
Describe the digestion and absorption of carbohydrates.
4.
Discuss the role of dietary fiber in human nutrition.
5.
Discuss the problems that can occur with carbohydrate digestion and absorption.
6.
State the recommended intake of dietary carbohydrate.
7.
Identify the chemical and physical properties of artificial sweeteners.
8.
Explain the roles of hormones in the regulation of blood glucose.
9.
Compare and contrast two major forms of diabetes mellitus, Type I and Type II.
LECTURE NOTES
I. Carbohydrates – An Introduction
II. Structures and Functions of Simple Carbohydrates
A. Most CHO composed of carbon, hydrogen, and oxygen
B. Monosaccharides: Glucose, Fructose, and Galactose
1. Glucose
a. principal monosaccharide
b. also called dextrose or blood sugar
c. Hexose
2. Fructose
a. also called levulose
b. food sources
c. hexose
d. conversion
3.
Galactose
a. structural difference
b. combines with glucose
c. conversion
4. Ribose (DNA)
a. found in cell’s genetic material
b. produced from other foods
c. pentose
5. Sugar alcohols
C. Disaccharides: Maltose, Sucrose, and Lactose
1. Oligosaccharides
a. contain 2 to 10 simple sugar units
b. disaccharides = 2 sugar units
2. Condensation reactions – alpha and beta bonds
3. Maltose
a. glucose + glucose (alcoholic beverages)
b. alpha bond
c. fermentation
4. Sucrose
a. glucose + fructose (table sugar)
b. alpha bond
c. found in plants
5. Lactose
a. glucose + galactose (primary sugar in milk and milk products)
b. beta bonds
c. role of lactase enzyme
d. lactose intolerance
D. Larger Oligosaccharides: Raffinose and Stachyose
1. Found in beans and legumes
2. Cannot be broken down by digestive enzymes
3. Bacteria metabolize then and produce gas and other by-products)
4. Beano
a. enzyme preparation made from mold
b. breaks down many of the indigestible oligosaccharides
III. Structures and Functions of the More Complex Carbohydrates
A. Digestible Polysaccharides: Starch and Glycogen
1. Glucose synthesis
2. Two types of plant starch
a. amylose and amylopectin
b. both linked by alpha bonds (digestible)
c. straight-chain vs. highly branched
d. food sources
e. amylopectin used as modified food starch
3. Glycogen
a. storage form of carbohydrate in humans and other animals
b. glucose polymer with alpha bonds and numerous branches
c. liver glycogen can be converted to glucose
d. muscle glycogen cannot be converted to glucose
B. Indigestible Polysaccharides: Dietary Fiber
1. Dietary fibers are composed primarily of nonstarch polysaccharides
a. Cellulose
b. Hemicellulose
c. Pectins
d. Gums
e. Mucilages
f. Lignins (non carbohydrate components of dietary fiber)
2. Insoluble fibers
a. cellulose, hemicellulose, and lignins
b. do not dissolve in water
3. Soluble fibers
a. pectins, gums, mucilages
b. swell or dissolve in water
c. yield 3 kcal/g when metabolized
IV. Carbohydrate Digestion and Absorption
A. Carbohydrate Digestion
1. Salivary amylase mixes with starchy products
2. In stomach, amylase inactivated by acidic environment
3. Further carbohydrate digestion occurs in the small intestine
4. Amylase from pancreas breaks down starch into maltose
5. Enzymes in intestinal wall digest disaccharides
B. Carbohydrate Absorption
1. Active absorption
a. glucose
b. galactose
2. Facilitated diffusion
a. fructose
3. 5% escapes digestion
V. Functions of Glucose and Other Sugars in the Body
A. Yielding Energy
1. Source of energy to body cells and some tissues
B. Sparing Proteins from Use as an Energy Source
1. Glucose is protein-sparing
2. Gluconeogenesis
C. Preventing Ketosis
1. Ketone bodies
2. Body needs 50-100 grams of carbohydrate per day to ensure complete fat metabolism
3. Type I diabetes
D. Imparting Flavor and Sweetness to Foods
1. Sugars vary in sweetness on a per gram basis
2. Sugars improve palatability of many foods
VI. Functions of Dietary Fiber
A. Health benefits
1. Diverticulitis
2. Hemorrhoids
3. Weight control and reduced risk of developing obesity
4. Associated with decrease in colon cancer development
5. Slows glucose absorption from the small intestine
6. Inhibits absorption of cholesterol and bile acid from small intestines
VII. Expert Opinion: The Benefits of a High Carbohydrate Diet
VIII. Recommended Carbohydrate Intakes
A. How Much Dietary Fiber Do We Need?
1. 20-35 grams per day
2. For children over 2 years, experts recommend a fiber intake of age + 5 g/day
4. Avoiding a carbohydrate-rich diet (High triglycerides/Syndrome X)
B. Problems of High Fiber Diets
1. Requires high fluid intake
2. Diets containing 60 grams per day may pose health risks
3. Intestinal gas
4. Phytobezoars in stomach
C. Moderating in Intake of Simple Sugars Is Important for Many of Us
1. No more than about 10% of total energy intake
2. About 50 grams of simple sugar (or 10 teaspoons) per day based on 2000 kcal diet
3. During food processing, simple sugar content is often increased
D. Problems With High Sugar Diets
1. Diet Quality
a. crowds out nutrient-dense foods
2. Dental Caries
a. cariogenic carbohydrates
3. High Glycemic Index
a. definition
b. influences
c. effects
E. Moderation in Lactose Is Important for Some People
1. Lactose intolerance is estimated to present in about 75% of the world’s population
2. Ways to overcome
IX. Carbohydrate in Foods: Food Sweeteners
A. Nutritive Sweeteners
1. Sugars
a. all monosaccharides and disaccharides discussed earlier are designated nutritive
sweeteners
b. high fructose corn syrup is about 40%-90% fructose
c. turbinado sugar
d. brown sugar
e. maple syrup
f. honey
honey is not safe for infants because it may contain spores of Clostridium botulinum
2. Sugar Alcohols
a. sorbitol, mannitol, and xylitol
b. contribute energy 1.5-3.0 kcal/g
c. metabolized and absorbed as glucose more slowly than simple sugars
d. in large amounts (50 grams) may have a laxative effect
B. Alternative Sweeteners
1. Saccharin
a. oldest alternative sweetener
2. Aspartame
a. Methyl ester of aspartic acid and phenylalanine
b. Nutrasweet/Equal
not heat resistant
PKU warning
3. Acesulfame-K
a. Sunette
b. not digested by body
c. used in baking
4. Sucralose
Splena
Used in baking
e. Other Alternative Sweeteners
Alitame
D-Tagatose
Stevia
Thaumatins
X. Nutrition Perspective: When Blood Glucose Regulation Fails
A. Regulation of Blood Glucose
B. Diabetes Mellitus
1. Type 1 Diabetes
2. Type 2 Diabetes
C. Hypoglycemia
Reactive
Fasting
ACTIVITIES, EXERCISES, AND ASSIGNMENTS (in Text)
1.
Ask students to consult the yellow pages of a telephone directory for advertisements by
chiropractors, hemopaths, naturopaths, and health/diet food stores offering treatment and products
for constipation and “irregularity.” Investigate other possible sources of advertising for laxative
products and “colonic irrigation” that might be found in local newspapers and magazines. Discuss
the cost of these treatments and determine if there is a potential for harm from such treatments or
products.
2.
Visit pharmacies, supermarkets, and health food stores to determine the types of laxatives and
diarrhea medications offered for sale. Make a list of these OTC drugs and medications that promise
relief from gastrointestinal disorders. Read labels and determine active ingredients in these products.
Do any come with warning labels?
3.
Visit health-food stores selling enzymes and other aids to digestion. Where are these products made
and what are the basic ingredients? What sort of health claims do they make? Discuss the potential
harm in taking megadoses of these enzymes.
4.
Have students watch television commercials for several evenings (particularly around the dinner
hour) and record the number of commercials devoted to promoting OTC laxatives, antacids and
products to treat heartburn. Determine the volume of advertising devoted to these products in the
local market. Consult marketing specialists for the dollar volume of business generated by these
products.
5.
Using the previous print out from FoodWorks diet analysis assignment, determine the fiber intake in
a day's menu. Discuss how students can increase their fiber intake. Sort foods by their content of
water-soluble and water-insoluble fibers.
6.
Using the students’ 3 day diet records, have them separate 1 days food intake into protein, fat,
carbohydrate, alcohol and hydrating beverages. Have them diagram the digestion and absorption
pathways for their foods, according to the macronutrient composition.
7.
Complete the following student assignment to discover what diet changes and possible treatment
need to be made to adjust when the lactase enzyme fails to function.
STUDENT ASSIGNMENT
LACTOSE INTOLERANCE
Talk with a person who has been diagnosed with lactose intolerance. Consider helping this person learn
more about the intolerance and how to best adjust.
1.
What are the major complaints or symptoms?
2.
What physiologically has caused these symptoms?
3.
Persons with lactose intolerance usually have individual intolerances. Which dairy foods cannot be
tolerated? (Be specific as to which kinds of cheeses, milks, yogurt, etc.)
4.
How can this individual ensure getting enough calcium in the diet with these food limitations? What
alternative calcium rich food choices do they have?
5.
What commercial products are available to be taken or chewed to increase the tolerance of fluid
milk? (List product names and the forms in which they can be purchased, such as in tablet, liquid,
etc.)
6.
On what basis do these commercial products work?
7.
What are the directions for their safe use?
ANNOTATED REFERENCES AND READINGS (Annotated References in
Text)
1.
Eastwood, MA: The physiological effect of dietary fiber: an update; Action of fiber along the
gastrointestinal tract. Annual Review of Nutrition 12:23-29, 1992.