CHAPTER 4 CARBOHYDRATES

The Carbohydrates:
Sugar, Starch,
Glycogen, and Fiber
Chapter 4
Sizer and Whitney, Nutrition: Concepts and Controversies, 15th
Edition. © 2020 Cengage. All Rights Reserved. May not be
scanned, copied or duplicated, or posted to a publicly accessible
website, in whole or in part.

Sizer and Whitney, Nutrition: Concepts and Controversies, 15th Edition. © 2020 Cengage. All Rights Reserved.
May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.
Learning Objectives
• Explain how plants synthesize carbohydrates
• Explain why carbohydrates are needed in the diet
• Describe how carbohydrates are converted to glucose in
the human body
• Describe the body’s handling of glucose
• Briefly summarize the differences among type 1 diabetes,
type 2 diabetes, and hypoglycemia
• Identify foods that are rich in carbohydrates
• Itemize the effects of added sugars on health

Carbohydrates
• Carbohydrates contain ideal nutrients that:
• Meet the body’s energy needs
• Feed the brain and the nervous system
• Keep the digestive system fit
• Keep your body lean
• Carbohydrates can be digestible and indigestible
• Complex carbohydrates
• Starch and fiber
• Simple carbohydrates
• Sugars

A Close Look at Carbohydrates
• Carbohydrates contain the sun’s radiant energy
• Green plants make carbohydrates
• Photosynthesis
• The process by which green plants make carbohydrates from carbon
dioxide and water using the green pigment chlorophyll to capture the
sun’s energy
• Carbohydrate-rich foods include plants and milk

Figure 4.1: Carbohydrate Is Made by
Photosynthesis

Sugars (Slide 1 of 2)
• Six sugar molecules are important in nutrition
• Three of these are:
• Monosaccharides: Glucose, fructose, and galactose
• Glucose is the most important monosaccharide in the human body
• The other three are:
• Disaccharides: Lactose, maltose, and sucrose
• All of their chemical names end in ose

Sugars (Slide 2 of 2)
• Monosaccharides
• Single sugar units
• Absorbed directly into the blood
• Disaccharides
• Pairs of single sugars linked together
• Digested and broken down by enzymes

Figure 4.2: How Monosaccharides Join to
Form Disaccharides
aGalactose does not occur in foods singly but only as part of lactose.
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, p. 124). Appendix A presents more detailed structures.

Starch, Glycogen, and Fibers
• Starch
• A plant’s storage form of glucose
• Packed in granules in a plant’s seeds
• Polysaccharides: Another term for complex carbohydrates;
compounds composed of long strands of glucose units linked
together
• Glycogen
• Animal storage form of glucose
• Fibers
• Supporting structures of a plant
• Digestion involves fermentation

Figure 4.3: How Glucose Molecules Join to
Form Polysaccharides
Starch
(branched)
Starch
(unbranched)
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
cannot 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.

The Need for Carbohydrates (Slide 1 of 2)
• Glucose is a critical and primary energy source
• Facilitates cell-to-cell communication
• Facilitates nerve and brain cell functioning
• The body tissues use carbohydrate for energy and other
critical functions
• The brain and nerve tissues prefer carbohydrate as fuel,
and red blood cells can use nothing else
• Intakes of refined carbohydrates should be limited

The Need for Carbohydrates (Slide 2 of 2)
• Carbohydrates have been wrongly accused of being the
“fattening” ingredient of foods
• For weight loss:
• Control caloric contribution
• Conversion into fat is inefficient
• Refined sugars contain no other nutrients
• Increase fiber-rich whole-food carbohydrate sources
• Reduce foods high in refined grains and added sugars

Why Do Nutrition Experts Recommend
Fiber-Rich Foods? (Slide 1 of 2)
• People who regularly eat fiber-rich fruit, legumes,
vegetables, nuts, seeds, and whole grains are often
reported to be healthier than those who do not
• There are two types of fibers:
• Soluble fibers
• Readily dissolve in water
• Many kinds are readily fermented
• Insoluble fibers
• Not viscous
• Retain shape and texture

Why Do Nutrition Experts Recommend
Fiber-Rich Foods? (Slide 2 of 2)
• Health benefits of fiber-rich foods:
• Reduce risk of heart disease and stroke
• Diets rich in fruit, legumes, vegetables, nuts, seeds, and whole grains
• Other complex carbohydrates
• Reduce risk of diabetes
• Metabolic diseases that impair a person’s ability to regulate blood
glucose
• Reduce risk of colon and rectal cancer
• Improve digestive tract health
• Promote healthy body weight
• Appetite control
• Less energy per bite

Figure 4.6: Characteristics, Sources, and
Health Effects of Fibers
aInulin, a soluble and fermentable but nonviscous fiber, is found naturally in a few vegetables, but is also purified from chicory root for use
as a food additive.
bPsyllium, a soluble fiber derived from seed husks, resists fermentation and is used as a laxative and food additive.

Figure 4.7: One Way Fiber in Food May Lower
Cholesterol in the Blood
High-fiber diet: More
cholesterol (in bile) is
carried out of the body.
Low-fiber diet: More
cholesterol (from bile) is
reabsorbed and returned
to the bloodstream.
1 - The liver acts something like a
vacuum cleaner, sucking up
cholesterol from the blood, using it to
make bile, and discharging the bile
into its storage bag, the gallbladder.
2 - The gallbladder empties its bile
into the intestine, where bile
performs necessary digestive tasks.
3 - In the intestine, some of the
cholesterol in bile associates with
fiber.
4 - Fiber carries cholesterol in bile
out of the digestive tract with the
feces.
5 - The cholesterol that remains in
the intestine is reabsorbed into the
bloodstream.

Digestive Tract Health (Slide 1 of 2)
• Supported by soluble and
insoluble fibers
• Ample fluid intake
• Benefits of fiber
• Protects against constipation,
hemorrhoids, appendicitis,
and diverticulosis

Digestive Tract Health (Slide 2 of 2)
• Hemorrhoids: Swollen, hardened (varicose) veins in the
rectum, usually caused by pressure resulting from
constipation
• Appendicitis: Inflammation and/or infection of the
appendix
• Diverticula: Sacs or pouches that balloon out of the
intestinal wall, caused by weakening of the muscle layers
that encase the intestine

Fiber Intakes and Excesses
• Few people in the U. S. meet recommendations
• 14 grams per 1,000 calories of total fiber
• Add fiber by substituting plant sources for animal sources
• Too much fiber?
• Use purified fibers with moderation
• Binders in fiber
• Chelating agents: Molecules that attract or bind with other
molecules and are therefore useful in either preventing or
promoting movement of substances from place to place

Table 4.3: Usefulness of Carbohydrates
(Slide 1 of 2)
Carbohydrates in the Body Carbohydrates in Foods
Energy source. Sugars and starch from
the diet provide energy for many body
functions; they provide glucose, the
preferred fuel for the brain and nerves
Flavor. Sugars provide sweetness
Glucose storage. Muscle and liver
glycogen store glucose
Browning. When exposed to heat, sugars
undergo browning reactions, lending
appealing color, aroma, and taste
Raw material. Sugars can be partly
broken down to fragments that are used
in making other compounds, such as
certain amino acids (the building blocks
of proteins), as needed
Texture. Sugars help make foods tender.
Cooked starch lends a smooth, pleasing
texture
Structures and functions. Sugars interact
with protein molecules, affecting their
structures and functions
Gel formation. Starch molecules expand
when heated and trap water molecules,
forming gels. The fiber pectin forms
the gel of jellies when cooked with sugar
and acid from fruit

Table 4.3: Usefulness of Carbohydrates
(Slide 2 of 2)
Carbohydrates in the Body Carbohydrates in Foods
Digestive tract health. Fibers help
maintain healthy bowel function (reduce
risk of bowel diseases)
Bulk and viscosity (thickness).
Carbohydrates lend bulk and increased
viscosity to foods. Soluble, viscous fibers
lend thickness to foods such as salad
dressings
Blood cholesterol. Fibers promote
normal blood cholesterol concentrations
(reduce risk of heart disease)
Moisture. Sugars attract water and keep
foods moist
Blood glucose. Fibers modulate blood
glucose concentrations (help control
diabetes)
Preservative. Sugar in high concentrations
dehydrates bacteria and preserves the
food
Satiety. Fibers and sugars contribute to
feelings of fullness
Fermentation. Carbohydrates are
fermented by yeast, a process that causes
bread dough to rise and beer to brew
Body weight. A fiber-rich diet is
conducive to a healthy body weight
N A

Whole Grains
• The Dietary Guidelines for Americans recommend that at
least half of daily grains should be whole grains
• Recommended flour types
• Four parts of the kernel
• Germ
• Endosperm
• Bran
• Husk

Figure 4.9: A Wheat Plant and a Single
Kernel of Wheat

Enrichment of Refined Grains
• The U. S. Enrichment Act for refined grain
• 1942: Iron, thiamin, riboflavin, and niacin
• 1996: Folate added to the list
• Whole grain foods superior to enriched grain foods
• Vitamin B6, magnesium, zinc, fiber, and phytochemicals

Figure 4.10: Nutrients in Whole-Grain,
Enriched White, and Unenriched White
Breads

Health Effects of Whole Grains
• Whole-grain intakes provide health benefits beyond just
nutrients and fiber
• Three daily servings of whole grains often have healthier
body weights and less body fat than other people
• Fill up the stomach
• Slow down digestion
• Promote longer-lasting feelings of fullness than refined grains
• Lower risks of heart disease, type 2 diabetes, and death
• A diet rich in whole grains is associated with reduced
risks of overweight and certain chronic diseases

Finding the Real Whole-Grain Foods (Slide 1
of 2)
• Not every choice
must be 100%
whole grain
• Misleading labels
• High fiber
• Brown color
• Label subtleties
• Cereals
• Limit intake of any
cereal, hot or cold,
with a high sugar,
sodium, or saturated
fat content
A Sampling of Whole Grains
Amaranth, a grain of the ancient Aztec peoplea
Barley (hulled but not pearled)b
Buckwheata
Bulgur wheat
Corn, including whole cornmeal and popcorn
Millet
Oats, including oatmeal
Quinoa (KEEN-wah), a grain of the ancient Inca
peoplea
Rice, including brown, red, and others
Rye
Sorghum (also called milo), a drought-resistant
grain

Finding the Real Whole-Grain Foods (Slide 2
of 2)
A Sampling of Whole Grains
Teff, popular in Ethiopia, India, and Australia
Triticale, a cross of durum wheat and rye
Wheat, in many varieties such as spelt, emmer, farro, einkorn, durum; and forms
such as bulgur, cracked wheat, and wheatberries
Wild ricea
aAlthough not botanical grains, these foods are similar to grains in nutrient contents, preparation, and use.
bHulling removes only inedible husk; pearling removes beneficial bran.

Figure 4.11: Bread Labels Compared

From Carbohydrates to Glucose
• To obtain glucose from newly eaten food:
• The digestive system must first render the starch and
disaccharides from the food into monosaccharides that can be
absorbed through the cells lining the small intestine
• Starch digestion begins in the mouth
• Enzymes split starch into shorter units
• Digestion ceases in the stomach but resumes in the small intestine
• Resistant starch: The fraction of starch in a food that is digested
slowly, or not at all, by human enzymes

Digesting Sugars and Fiber
• Sugars
• Split to yield free monosaccharides
• Enzymes on the small intestine lining
• Travel to the liver
• Fiber
• Fermented by bacteria in the colon

Figure 4.12: How Carbohydrate in Food
Becomes Glucose in the Body

Why Do Some People Have Trouble
Digesting Milk?
• Ability to digest milk carbohydrates varies
• Lactose intolerance: Impaired ability to digest lactose due to
reduced amounts of the enzyme lactase
• Also called milk allergy
• Insufficient production of lactase enzyme of the small intestine
splits the disaccharide lactose to monosaccharides
• Symptoms of intolerance
• Nausea, pain, diarrhea, and excessive gas
• Nutritional consequences
• Replace its protein, calcium, and vitamin D in the diet

Table 4.7: Lactose Intolerance Strategies
Product Effects/Strategies
Aged cheeses Bacteria or molds used to create cheeses ferment lactose
during the aging process. Use in moderation
Lactase pills and drops Lactase added to milk products by consumers or pills
taken before milk product consumption split lactose
molecules in the digestive tract. Harmless when used as
directed by the manufacturer
Lactase-treated milk
products
Lactase added to milk products during manufacturing
splits lactose before purchase. Use freely in place of
ordinary milk products
Milk substitutes (soy, pea,
nut, or grain beverages),
cheese and yogurt
substitutes
Nonmilk replacements for milk products may or may not
be fortified with the nutrients of milk. Compare Nutrition
Facts panels for calcium, protein, and vitamin D in
particular
Yogurt (live culture type) Yogurt-making bacteria can survive in the human digestive
tract; the bacteria possess an enzyme to split lactose
Yogurt (with added milk
solids listed on the label)
These contain extra lactose and can overwhelm the
system

The Body’s Use of Glucose
• Basic carbohydrate unit used for energy
• The body handles glucose judiciously
• Maintains internal store
• Tightly controls blood glucose concentration
• The brain stores a tiny fraction of the total as an
emergency reserve to fuel the brain for an hour or two in
severe glucose deprivation

Splitting Glucose for Energy (Slide 1 of 3)
• Glucose is broken in half
• Can be reassembled
• Is broken into smaller
molecules
• Irreversible
• Two pathways

• Glucose can be converted to fat
• Body fat cannot be converted to glucose to feed the brain
adequately
• Depends on protein when there is insufficient carbohydrate
• Protein-sparing action of carbohydrate
• Ketosis: An undesirably high concentration of ketone
bodies, such as acetone, in the blood or urine
• Shift in body’s metabolism caused by the use of ketone bodies for
energy
• Ketone bodies: An undesirably high concentration of ketone bodies,
such as acetone, in the blood or urine
• Can disrupt the acid-base balance in blood

• D R I
• Recommends at least 130 grams of carbohydrate a day
• Much more is recommended to maintain health and glycogen stores

How Is Glucose Regulated in the Body?
(Slide 1 of 2)
• Blood glucose levels should not be too high or too low
• Two safeguard activities to maintain blood glucose:
• Siphoning off excess blood glucose
• Replenishing diminished glucose
• Two hormones prove critical to these processes:
• Insulin
• Stimulates glucose storage as glycogen
• Glucagon
• Helps release glucose from storage

Figure 4.15: Blood Glucose Regulation—
An Overview

How Is Glucose Regulated in the Body?
(Slide 2 of 2)
• Muscles hoard two-thirds of the body’s total glycogen
• The liver stores the remainder and is generous with its
glycogen releasing glucose into the bloodstream for the
brain or other tissues when the supply runs low

Excess Glucose and Body Fatness
• Two Ways to Handle Excess Glucose:
• Body tissue shift
• Burn more glucose: Fat is left to circulate and be stored
• Carbohydrate and weight management
• Carbohydrate is stored as fat, and weight is maintained through dietary
importance and composition

The Glycemic Index of Food
• A ranking of foods according to their potential for raising
blood glucose relative to a reference dose of glucose
• Measures the degree of elevation of blood glucose and insulin
• Food score
• A steady diet of high-glycemic ultra-processed foods may
be linked with chronic diseases
• Metabolism affects the body’s insulin response
• Diabetes
• Type 1 diabetes: The pancreas fails to produce insulin
• Type 2 diabetes: Body cells fail to respond to insulin

Think Fitness (Slide 1 of 2)
• A working body needs carbohydrate fuel to replenish
glycogen, and when it runs low, physical activity can seem
more difficult. If your workouts seem to drag and never get
easier, take a look at your eating pattern. Are your meals
regularly timed? Do they provide abundant carbohydrate
from nutritious whole foods to fill up glycogen stores so they
last through a workout?
• Here’s a trick: at least an hour before your workout, eat a
small snack of about 300 calories of foods rich in complex
carbohydrates and drink some extra fluid. Remember to cut
back your intake at other meals by an equivalent amount to
prevent unwanted weight gain

Think Fitness (Slide 2 of 2)
• The snack provides glucose at a steady rate to spare
glycogen, and the fluid helps maintain hydration
• Start now! Choose a one-week period and have a healthy
carbohydrate-rich snack of about 300 calories, along with a
bottle of water, about an hour before you exercise. Be sure
to track your diet in Diet & Wellness Plus in MindTap during
this period so that you can accurately determine your total
calorie intake. Did you have more energy for exercise after
you changed your eating plan?

Table 4.8: Low Glycemic Index of Selected
Foods
Note: Using the glucose reference scale, foods are classified as low (55 or less), medium (56 to 69), or high (70 or greater).
aProtein foods that contain little or no carbohydrate (such as meats, poultry, fish, and eggs) do not raise blood glucose, and therefore do not
have a glycemic index.
Source: Adapted from F. S. Atkinson, K. Foster-Powell, and J. C. Brand-Miller, International tables of glycemic
index and glycemic load values: 2008, Diabetes Care 31 (2008): 2281–2283.
Grains Fruit Vegetabl
es
Milk
Products
Protein
Foodsa
Other
Barley,
chapati,
corn
tortilla,
rice
noodles,
rolled
oats,
pasta
Apple,
apple juice,
banana,
dates,
mango,
orange,
orange
juice,
peaches
(canned),
strawberry
jam
Carrots,
corn
Ice
cream,
milk, soy
milk,
yogurt
Legumes Chocolate
candy

Table 4.8: Medium Glycemic Index of Selected
Foods
Grains Fruit Vegetable
s
Milk
Products
Protein
Foodsa
Other
Brown
rice,
couscous
Pineapple Potatoes
(French
fries),
sweet
potatoes
N A N A Popcorn,
potato
chips,
soft
drinks
aProtein foods that contain little or no carbohydrate (such as meats, poultry, fish, and eggs) do not raise blood glucose, and therefore do
not have a glycemic index.

Table 4.8: High Glycemic Index of Selected
Foods
Grains Fruit Vegetables Milk
Products
Protein
Foodsa
Other
Breads,
breakfast
cereals,
white rice
Watermelon Potatoes
(boiled)
N A N A Rice
crackers
aProtein foods that contain little or no carbohydrate (such as meats, poultry, fish, and eggs) do not raise blood glucose, and therefore do
not have a glycemic index.

Diabetes (Slide 1 of 2)
• In some people, blood glucose regulation fails, causing
either diabetes or hypoglycaemia
• An abnormally low blood glucose concentration, often
accompanied by symptoms such as anxiety, rapid heartbeat, and
sweating
• Blood glucose rises after a meal and remains above
normal
• Insulin is either inadequate or ineffective

Diabetes (Slide 2 of 2)
• Abnormally high blood glucose
• Type 1 diabetes: Blood glucose stays too high
• Insulin is lacking
• Often diagnosed in childhood
• Type 2 diabetes: Blood glucose stays too high
• The cells do not respond to normal insulin levels
• Often diagnosed in adulthood
• Occurs as a consequence of obesity
• To achieve stable blood glucose:
• Control carbohydrate and calorie intake
• Exercise appropriately
• Take insulin injections or medications

Hypoglycemia
• Rare disease
• Abnormally low blood glucose
• Symptoms
• Weakness, irregular heartbeats, sweating, anxiety, hunger,
trembling, and, rarely, seizures and loss of consciousness
• Causes
• Poorly managed diabetes
• Too much insulin
• Too much strenuous or physical activity
• Inadequate food intake
• Illness

Finding the Carbohydrates in Foods (Slide 1 of
3)
• Fruits
• Vary in water, fiber, and sugar concentrations
• Limit juice intake
• Vegetables
• Starchy vegetables are major contributors of starch in the diet
• Grains
• Low-fat and low-sugar choices

3)
• Protein foods
• Nuts and legumes
• Milk and milk products
• Generous contributor of carbohydrate
• Oils, solid fats, and added sugars
• Devoid of carbohydrate
• Added sugars provide almost pure carbohydrate
• Honey

3)
• Sugar alcohols
• Provide fewer calories than sugars
• Lower glycemic response
• Don’t cause dental caries
• Nature of sugar
• Each teaspoonful of any sweet can be assumed to supply about 4
grams of carbohydrate

Controversy 4:
Are Added Sugars “Bad” for You?
• Do added sugars cause obesity?
• Americans have grown fatter in past decades
• Top calorie sources: Sugary foods and beverages

Figure C4.1: Increases in Adult Body
Weight over Time
Source: C. D. Fryar and coauthors, National Center for Health Statistics, Anthropometric reference data for children and
adults: United States, 2011–2014 Vital and Health Statistics 38 (2016), available at www.cdc.gov/nchs/data/series
/sr_03/sr03_039.pdf.

Figure C4.2: Daily Energy Intake over Time
Source: U.S. Department of Agriculture, Agricultural Research Service Energy Intakes, Percentages of energy from protein,
carbohydrate, fat, and alcohol, by gender and age, What We Eat in America, NHANES 2013–2014, (2016), available at
https://www.ars.usda.gov/ARSUserFiles/80400530/pdf/1314/Table_5_EIN_GEN_13.pdf; E. S. Ford and W. H. Dietz, Trends in
energy intake among adults in the United States: Findings from NHANES, American Journal of Clinical Nutrition 97 (2013): 848–
853.

Figure C4.3: Sources of Added Sugars in
the U.S. Diet
Sources: U.S. Department of Health and Human Services and U.S. Department of Agriculture, 2015–2020 Dietary
Guidelines for Americans, 8th edition (2015), available at http://health.gov/dietaryguidelines/2015/guidelines/.

Do Added Sugars Cause Diabetes?
• Added sugars may raise blood pressure, and blood
pressure plays a critical role in the health of the heart
• To reduce the risk of diabetes:
• Maintain healthy body weight
• Limit alcohol intake
• Eat according to the Dietary Guidelines for Americans

Do Liquid Calories Pose Special Risks?
• Affect appetite control
• People’s expectations
• Easily gulped down
© Polara Studios, Inc.

Hints of Metabolic Mayhem
• Some important metabolic links exist among added
sugars, obesity, and chronic diseases
• Insulin
• Insulin resistance: Body cells fail to respond to insulin’s effects
• Fructose
• Handled differently in the body
• Affects appetite differently
• Body fatness and blood lipids
• Stimulates the liver to synthesize new fat molecules that can be stored
in adipose tissue and this can cause damaging non-alcoholic fatty liver
disease (N A F L D)

Figure C4.4: Glucose and Fructose in
Common Added Sugars
aA typical mixture; others exist.

High-Fructose Corn Syrup (H C F S)
• Is H C F S more harmful than sucrose?
• Research indicates virtually identical metabolic effects
• All common added sugars are similar
• Shouldn’t be consumed in excess

CHAPTER 4 CARBOHYDRATES

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