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Chapter 4 – The Carbohydrates: Sugars, Starches, and Fibers
Learning Objectives
After completing Chapter 4, the student will be able to:
1. Classify carbohydrates as mono-, di-, or polysaccharides.
2. Explain the two major types of dietary fibers and their uses in the body.
3. Trace the digestion and absorption of carbohydrates.
4. List the enzymes used in the digestion of carbohydrates.
5. Describe lactose intolerance symptoms, prevalence, and treatment.
6. List the major uses of glucose in the body.
Assignments and Other Instructional Materials
The following ready-to–use assignments are available in this chapter of the instructor’s manual:
• New! Case study
• Worksheet 4-1: Hidden Sugars—What Is Your Sugar IQ? 1
Other instructional materials in this chapter of the instructor’s manual include:
• Classroom activities
• Worksheet answer keys (as appropriate)
• New! Handout 4-1: Alternatives to Sugar
Lecture Presentation Outline4
“Of special interest to…” symbol key: = Hot Topic = Personal Health
= Health Care Professionals = Science Majors
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Key to instructor resource annotations (shown to the right of or below outline topics):
PL = Available on Power Lecture DVD-ROM (ISBN 0538797592): V = video
TRA = Transparency acetates: 12e TRA = 12th edition, 11e TRA = 11th edition, 10e TRA = 10th edition
I. The Chemist’s View of Carbohydrates 10e TRA 31
Carbohydrates are made of carbon, hydrogen, and oxygen atoms. These atoms form chemical bonds that follow
the laws of nature.
A. Monosaccharrides are single sugars (most are hexoses). 10e TRA 32, 33
1. Glucose serves as the essential energy source, and is commonly known as blood sugar or dextrose.
B. Disaccharides are pairs of monosaccharides, one of which is always glucose. 10e TRA 34, 35
1. Condensation reactions link monosaccharides together.
C. The Polysaccharides contain many glucose units bound/linked together in straight or
branched chains. 12e TRA 6
1. Glycogen
a. Storage form of glucose in the body.
b. Provides a rapid release of energy when needed.
3. Dietary fibers provide structure in plants, are very diverse, and cannot be broken down by human
enzymes. Website HN 4-2, 4-4
a. Soluble fibers are viscous and can be digested by intestinal bacteria (this property is also known
as fermentability). These fibers are found in fruits and vegetables.
II. Digestion and Absorption of Carbohydrates
The body breaks down starches and sugars to short glucose chains called dextrins. They are then broken down
A. Carbohydrate Digestion
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1. In the mouth, the salivary enzyme amylase begins to hydrolyze starch into short polysaccharides and
maltose.
B. Carbohydrate Absorption 10e TRA 37
1. Primarily takes place in the small intestine.
3. Fructose is absorbed by facilitated diffusion.
C. Lactose Intolerance IM CI 4.4
1. Symptoms include bloating, abdominal discomfort, and diarrhea.
3. Prevalence
a. Lowest in Scandinavians and northern Europeans.
b. Highest in Southeast Asians and native North Americans.
4. Dietary Changes
a. Increase consumption of milk products gradually.
b. Mix dairy with other foods.
III. Glucose in the Body
Through the study of sugars, known as glycobiology, researchers are uncovering many roles that glucose has in
the body. These include glucose’s interaction with protein and lipid molecules.
A. A Preview of Carbohydrate Metabolism
1. The body stores glucose as glycogen in liver and muscle cells.
4. Making ketone bodies from fat fragments
a. The accumulation of ketone bodies in the blood is called ketosis.
b. Ketosis upsets the acid-base balance in the body.
5. The body can use glucose to make body fat when carbohydrates are consumed excessively.
B. The Constancy of Blood Glucose 12e TRA 7
1. Maintaining Glucose Homeostasis
a. Low blood glucose may cause dizziness and weakness.
2. The Regulating Hormones
a. Insulin moves glucose into the cells and helps to lower blood sugar levels.
3. Balance glucose within the normal range by eating balanced meals regularly. IM CA 4-2
4. Blood glucose can fall outside the normal range with hypoglycemia or diabetes.
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5. Diabetes PL V “Diabetes Prevention”; IM CI 4.5
6. Hypoglycemia is low blood glucose and can often be controlled by dietary changes.
7. Glycemic response is how quickly the blood glucose rises and elicits an insulin response.
a. Glycemic index classifies foods according to their potential for raising blood glucose. 10e TRA 39
IV. Health Effects and Recommended Intakes of Sugars
Excessive intake of sugar may displace nutrients and contribute to obesity. Consuming foods with added
sugars should be limited. Naturally occurring sugars from fruits, vegetables and milk are acceptable sources.
A. Health Effects of Sugars – Foods with added sugars often have sugars listed as a first ingredient. Sugars
may include brown sugar, confectioners’ sugar, corn sweeteners, corn syrup, dextrose, granulated
sugar, high-fructose corn syrup, honey, invert sugar, levulose, maple sugar, molasses, raw sugar,
turbinado sugar, and white sugar.
1. Nutrient deficiencies may develop from the intake of empty kcalories.
B. Recommended Intakes of Sugars IM WS 4-1, CA 4-3, 4-4, CI 4.1
1. The USDA Food Guide states that added sugars can be included in the diet as part of discretionary
kcalories.
V. Alternative Sweeteners PL V “Diet Soda & Weight Gain”; IM HN 4-1, CI 4.6
A. Artificial sweeteners (nonnutritive sweeteners) provide little if any energy. Large doses can have
negative effects on health.
A. Health Effects of Starch and Fibers PL V “High-Fiber Foods: Benefits and Tips”
1. May be some protection from heart disease and stroke.
a. Soluble fibers bind with bile and thereby lower blood cholesterol levels.
b. Fiber may also displace fat in the diet.
2. Reduce the risk of type 2 diabetes by decreasing glucose absorption.
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B. Recommended Intakes of Starch and Fibers IM CI 4.1, 4.3
1. RDA for carbohydrate is 130 g per day, or 45%-65% of energy intake.
C. From Guidelines to Groceries IM WS 4-3, CI 4.2; Website HN 4-3
1. Grains – encourage whole grains.
2. Vegetables – starchy and nonstarchy vegetables differ in carbohydrate content.
VII. Highlight: Carbs, kCalories, and Controversies PL V “Diet Comparison”; IM CI Highlight
Many popular diet plans recommend carbohydrate restriction.
A. Carbohydrates’ kCalorie Contributions 12e TRA 8, 9
1. Carbohydrates have been blamed for increases in obesity.
2. Epidemiological studies have found that as carbohydrate intake increases, body weight decreases.
4. Weight loss is due to kcalorie restriction.
B. Sugars’ Share in the Problem
1. There has been an increase in the use of high-fructose corn syrup in manufactured food and soft drinks.
2. Cravings and Addictions – Carbohydrates may be sought out to increase the secretion of serotonin in
the brain, which elevates the mood. There is no physiological or pharmacological addiction that occurs
5. Energy Regulation – Sugar in liquid form cannot be detected, leading to higher energy consumption.
C. Insulin’s Response
1. Insulin resistance is a major health concern.
2. The Glycemic Index and Body Weight
a. In studies, a low-glycemic index diet did not show greater weight loss than for those following a
3. The Individual’s Response to Foods – Metabolism impacts insulin response.
D. In Summary
1. Restricting all carbohydrates is not recommended.
Case Study5
Frank P. is a 48-year-old landscape architect recently diagnosed with hypoglycemia from a glucose tolerance blood
test. He is 69 inches tall and weighs 202 pounds. His usual weight is 190 pounds; he reports an unexpected weight
gain of 12 pounds over the past 6 months. Frank reports he often skips breakfast or stops for a donut and coffee on
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his way to work in the morning. He often eats out with clients for lunch or he grabs a fruit smoothie on his way to a
job site. He eats dinner at home with his wife most evenings. He reports feeling hungry, weak, and “anxious” on
many occasions during his work day, which he says is relieved somewhat by eating a candy bar or other high-sugar
snack food. His diet history reveals no food intolerances although he states he avoids products which contain high–
fructose corn syrup and prefers to use products sweetened with sugar.
1. Which of Frank’s symptoms could be due to hypoglycemia? What dietary habits may be aggravating these
symptoms?
2. What are the similarities and differences between glucose and fructose that would be important for Frank to
understand when making decisions about his diet?
Answer Key
1. Weakness, anxiety, and hunger. Skipping meals, not eating at regular times, and eating high-sugar, low-protein
meals and snacks.
2. Glucose and fructose have the same chemical formula but vary in structure. Glucose and fructose together form
sucrose (table sugar). Glucose is the primary fuel and energy source for the brain, muscles, nerves, and other
body cells. Fructose is digested more slowly and causes a smaller rise in blood sugar than glucose. Foods that
contain both types of sugar should be eaten in moderation.
5. Eating balanced meals at regular intervals helps the body maintain a happy medium between the extremes of
blood sugars. Balanced meals that provide protein and carbohydrates, including fibers and a little fat, help to
slow down the digestion and absorption of carbohydrate so that glucose enters the blood more gradually.
Suggested Classroom Activities
An excellent way to begin this chapter is with a discussion of the brain’s dependence on glucose and the body’s
regulation of it. The concepts are new to the majority of beginning students, complex enough to be challenging but
simple enough to grasp, and of great personal interest.
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record what they ate for breakfast, and at what time. Collect the papers, eliminate those who ate more than 5 or
fewer than 2 hours earlier, sort the remaining ones into high-protein, low-protein, no-protein, and no-breakfast piles,
and average the energy scores.
In over two dozen demonstrations, the results have been in the expected direction: those who ate high-protein
breakfasts feel the most energetic; those with no-protein, least. (This only works for morning classes, of course.) If it
doesn’t “work,” explain what you would expect to see, and why. Criticize the demonstration as unscientific (it’s not
blind, there may be bias); but point out that it at least illustrates that a balanced breakfast can influence a morning’s
performance, while the many deviations from the average show that a multitude of other factors are working, too.
This exercise may help students remember that dietary protein influences blood glucose regulation—a first stone in
the foundation for understanding metabolism.
Classroom Activity 4-3: Sugar in Soda
Key concept: Added sugar content of soda Class size: Any
Materials needed: Sugar (at least 10 teaspoons), teaspoon for measuring, drinking glass of water
Classroom Activity 4-4: Sugar Content of Processed Foods
Key concept: Added sugar content of processed foods Class size: Any
Instructions: Have students read the packages of cereal boxes or other foods and record sugar contents on index
cards. Be sure to instruct them to look for other terms that also denote sugar. Discuss findings in class.
Classroom Activity 4-5: Fiber Content of Over-the-Counter Fiber Supplements
Key concept: Fiber sources Class size: Any
Classroom Activity 4-6: Scheduled Interruption: Think/Pair/Share
Objective: Reflection on content Class size: Any
Instructions: Examination of student attention levels throughout class indicate that students’ attention levels are the
highest during the first five minutes of class, then levels slowly decline throughout a lecture. To enhance students’
Critical Thinking Questions6
These questions will also be posted to the book’s website so that students can complete them online and e–mail their
answers to you.
1. Discuss in some detail the three different types of carbohydrates. In your discussion, explain how each type is
chemically different from the others, and how these differences relate to its activity and function.
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Answer: Monosaccharides: These are simple sugars that are made up of 6 carbon and 6 oxygen units with 12
hydrogen units. The three monosaccharides are:
• Glucose
• Fructose
Polysaccharides are very important for the body for several reasons. First, the body is able to store a limited
amount of energy in the form of glycogen. Glycogen is generally stored in the liver and muscle tissue and can
be released very quickly when needed. Athletes frequently work to increase their ability to store glycogen in an
effort to improve their performance abilities in endurance events.
Starches can be used for energy and for cooking purposes and are found in the grains and root vegetables such
as potatoes, yams, and parsnips, while fibers can be found in fruits, vegetables, and whole-grain foods. Fibers
serve as an important digestive aid to our bodies. Dietary fibers help to facilitate passage of food through the
intestines, thus reducing the time that digested food may sit in the intestinal tract, causing constipation and/or
inappropriate bacterial growth. There are two types of important fibers clients should be aware of: soluble
(which are found in oats, barley, and legumes) and insoluble (found in whole grains and vegetables).
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2. The importance of developing strong bone mineral density is dependent on the intake of a calcium-rich diet.
While there appears to be an abundance of dairy products available to individuals in the United States, there still
appears to be an increasing prevalence of bone diseases such as osteoporosis (thin or brittle bones). From your
readings, discuss why you think this may be a problem. What are your suggestions to help a client to avoid bone
issues, and why would these suggestions work with someone that has problems digesting lactose-containing
products?
Answer: This question is asking the student put together several disparate facts. For instance, the enzyme
lactase is most efficient at birth and in childhood. As a person ages, the enzyme’s efficiency declines. As
outlined in the text, lactose intolerance is also genetically linked. Given the ever increasing ethnic diversity of
Some people can tolerate “fermented products” such as yogurt better than regular milk products as well as some
of the hard cheeses such as parmesan. Digestive aids such as “Lactaid” are also helpful for those that can’t
tolerate any of the other above suggestions. As above, some individuals are able to tolerate dairy products to
some degree and still retain some lactase enzyme to enable them to process the lactose in their diets. However,
the types of dairy products they consume must be consumed in small amounts and the fermented products or
those that have some of the lactose removed are better tolerated by these individuals.
3. Obesity is a significant problem in this country, as are its comorbidities, heart disease, diabetes, and some
cancers. Describe how carbohydrates can play a role in the cause and in the prevention of obesity and its
subsequent comorbities. What types of assessment should be utilized as a diagnostic tool in the prevention and
treatment of obesity and its comorbidities?
Answer: Over ingestion of simple sugars, which is often accompanied with ingestion of fats, is a major
contributor to obesity in the United States. For example, the ingestion of sugar candies is often associated with
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Another frequently noted contributor to obesity in our country is our “biggie size” society. Most Americans do
not have any knowledge of portion sizing for any food product and product labels often provide misinformation
on portion control. Therefore, there are many areas within the production and distribution of simple sugars that
accentuate the issue of obesity.
Overconsumption of simple sugars is stored as fat and can lead to heart disease, stroke, diabetes, and some
cancers. Many diseases are a result of over accumulation of excess fat, plaque accumulation on the artery walls,
lack of exercise, and the body’s inability to continue to function in an environment that is wearing out all of its
control mechanisms. For example, in type 2 diabetes, an individual that is obese continues to call upon the
pancreas and all its hormones to work in a continually overloaded situation. Eventually, this system becomes
inefficient or stops operating.
It is also important to stress the importance of complex carbohydrates (polysaccharides) to clients who believe
that carbohydrates are “bad.” Carbohydrates are essential for energy, in particular brain energy and muscle
energy, something that many individuals do not understand. In addition, carbohydrates provide an important
source of B vitamins, fiber, and more. Deleting them from one’s diet does not improve health status.
The use of carbohydrate planning tools such as the glycemic index does assist some individuals that find
themselves very sensitive to consumption of carbohydrates. The glycemic index is a measure of the rise in
blood sugar caused by various carbohydrate-containing foods. For some individuals, particularly brittle
diabetics and hypoglycemics, use of the glycemic index can be very helpful. However, keep in mind that
product information is not always kept up to date nor does it account for the variety of foods in one product.
There are times that one individual may react slightly different than another. Finally, some foods rate differently
than would be expected: i.e., low-glycemic index foods are the complex carbohydrates while high-glycemic
foods are the simple sugars. With combined foods, some foods will react as a high-glycemic food when they are
expected to be a low-glycemic food.
4. Discuss the differences between type 1 diabetes and type 2 diabetes.
Answer: The key difference between type 1 and type 2 diabetes is the etiology, or root cause. Type 1 results
from autoimmune destruction of the pancreatic beta-cells that produce insulin. This leads to a decline in insulin
Type one diabetes is better known as juvenile diabetes; its cause is not fully known at this time. Onset is usually
in children between the ages of less than four years old to the teen years. Regulation of blood sugar does take
some time to achieve, but is achievable. Many of these children wear an insulin pump to deliver the insulin
automatically so that they do not have to be injected constantly. The issue with juvenile diabetes is the ability to
regulate the blood sugar and the sequelae of the disease such as blindness, vascular disease, etc. Medical
advances have helped considerably in the recent years; however, children of juvenile diabetes must always be
vigilant of their diets and blood sugar.
5. In this chapter, you have learned about the importance of carbohydrates in a number of facets. Carbohydrates
can serve as energy for the brain, storage energy for the muscles, and digestive aids. However, unlike proteins,
carbohydrates continue to be perceived as a “bad food” in the diet. Individuals may go to great length to “avoid”
carbohydrates but eat a “healthy diet.”
While some consumers may take a more moderate approach and use replacement or substitute sweeteners
(alternative sweeteners) to replace sucrose, use of a variety of foods should be the preferred route to a healthy
diet. Discuss the fallacies in thinking that alternative sweeteners can replace sugar and discuss the role of
alternative sweeteners in a dietary plan for a healthy adult.
Answer: Carbohydrates are very important in the diet as a source of energy for the body, brains, red blood cells,
and muscle. Carbohydrates are absorbed and quickly transported to the cells where they are metabolized to
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often hides the fresh flavors of vegetables and whole–grain pastas and rice.
Alternative sweeteners are a popular market item that has a place in the diet of the American public. Their use
has long been recognized for the diabetic that cannot add simple sugars to their diet; however, with a diet–
crazed American public, alternative sweetener sales are a multimillion dollar industry. Recognizing that “all
foods fit” in the diet of any individual, working with the consumer to moderate the use of alternative sweeteners
is the preferred approach.
If a consumer is consuming a great deal of high-fructose soda, the RD is encouraged to work with the consumer
so that they replace half of their regular soda consumption with one fourth water consumption and one fourth
diet soda consumption. Over time, the RD will try to reduce the soda consumption as well as the types until s/he
can achieve consumption of greater amounts of water and far less of either diet or regular soda, as neither
retains any nutritional value.
6. In Highlight 4 you learned a bit about the issues surrounding carbohydrates and weight gain. In the following
scenario, what advice would you recommend to the individuals and why?
You are visiting overnight with family relatives that you have not seen for some time. They have learned that
you are studying to become an RD. The mother of the family (your distant aunt) is quite overweight and the two
children, 12 y/o and 16 y/o, are “heavy” but you would not classify them as obese. The father of the family
recently had a heart attack and while in the hospital was put on a low-fat diet. He is not overweight by
observation.
Your aunt is trying to follow the diet “faithfully” for her husband and believes that having everyone in the
household follow the diet would be best (children included). The diet includes lean meats and low-fat dairy
products. Your aunt decided that the family should also cut out carbohydrates as well given that “they can cause
you to become fat” and is making sure that everyone is consuming plenty of liquids to wash away the plaque in
the arteries.
What do you think of this diet and what recommendations would you give to your aunt and her family?
Answer: One would have to start with a few questions here. I hope you’re asking the same questions! First,
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While fluids, particularly water, are important to the body, if many other types of fluids are consumed that add
calories and no other nutrition, this can be a problem. The RD student would want to assess this and discuss
with the family. Fluids are important for hydration but cannot remove plaque. Therefore, the aunt must be
advised about what fluids provide to the diet and what types of fluids are best for each individual.
Finally, each individual in this family should have a different goal, weight wise. While the uncle had the heart
attack, there can be many reasons other than weight for this. As indicated, his weight is within normal standards
for his height, but upon assessment (not provided in the case) of his lipid profile, his LDL is extremely high and
his HDL is very low. He has a family history of cardiac disease. Therefore, the uncle remains at high risk for
cardiovascular disease and will benefit from the low-fat, high-fiber diet.
The mother is in need of a weight-loss plan, which can be achieved by following the rest of the family’s
program of low-fat, moderate-protein, high-fiber foods and lots of exercise. Plenty of fresh water and sunshine
are also helpful in her success. If she becomes anxious, she is recommended to go to massage therapy or yoga,
etc. All of these approaches will help all of the family improve their health and overall well being.
IM Worksheet Answer Key
Worksheet 4-1: Hidden Sugars—What Is Your Sugar IQ?
Answers will vary depending on source of nutrition data used. Here are some example answers:
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Worksheet 4-2: Glycemic Index and Glycemic Load
Food
GL
Sugar (1 Tbsp.)
8 (8.16)
Worksheet 4-3: Check Your Carbohydrate Choices – Answers will vary.
Worksheet 4-4: Chapter 4 Crossword Puzzle
Worksheet 4-5: Carbohydrate Basics (Internet Exercise)
Canadian Information7
4.1 Canadian Recommendations for Intake of Sugars, Starch, and Fibre for Healthy People
The textbook describes recommended intakes for sugars on pages 114-115 and for starches and fibre on pages 120–
121. The Canadian guidelines and recommendations concerning dietary intake of carbohydrates are as follows:
Eating Well with Canada’s Food Guide
• Eat at least one dark green and one orange vegetable each day.
• Have vegetables and fruit more often than juice.
Dietary Reference Intakes (DRI)
• AMDR – 45-65% of total daily energy intake
Reference Daily Values on Food Labels
• Carbohydrate – 300 g
• Fibre – 25 g
Diet-related Health Claim
• A healthy diet rich in a variety of fruits and vegetables may help reduce the risk of some types of cancer.
Apple (1 med.)
38
16
6 (6.08)
low
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11
8 (7.92)
low
White rice (1 c.)
64
52
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4.2 Labelling of Carbohydrates in Canada
Due to widespread use of the term “carb” in the marketplace, Canadian Food Inspection Agency (CFIA) will not
object to the use of the term “carb” as an abbreviation for “carbohydrate” when used in the context of nutrient
content claims or as part of a quantitative statement. However, CFIA objects to use of “carb” in the Nutrition Facts
4.3 Carbohydrate Intake of Canadians
The Canadian Community Health Survey (CCHS), Cycle 2.2 on Nutrition, conducted in 2004, collected 24-hour
dietary recall and related data including physical activity, chronic health conditions, lifestyle choices, food security,
sociodemographic data, and measured heights and weights from a nationally-representative sample of Canadians
across the nation. A second 24-hour dietary recall was also obtained from a representative sub-sample of the original
group. The report, Overview of Canadians’ Eating Habits, generated from the CCHS data and released in July 2006,
indicates carbohydrates comprise an average of approximately 50% of total daily caloric intake for Canadian
adults.11 This level of average intake is within the suggested AMDR for carbohydrates.
A subsequent publication, Nutrient Intakes from Food: Provincial, Regional and National Summary Data Tables,
Volume 1, released in 2007, reported summary tables comparing the usual intake of the 13 core nutrients found on
the Nutrition Facts table on food labels to the DRIs. These nutrients include: energy, 6 nutrients presented as percent
of total energy intake (fats, proteins, carbohydrates, saturated fats, monounsaturated fats, and polyunsaturated fats)
and 6 nutrients in absolute amounts (total dietary fibre, cholesterol, vitamin A, vitamin C, calcium, and sodium).
This is the first of three volumes of summary tables generated from data collected in the CCHS, Cycle 2.2: Nutrition
4.4 Lactose Intolerance
Students may find the Dietitians of Canada fact sheet on lactose intolerance, titled Milk Matters, a useful companion