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117
Chapter 7 – Energy Metabolism
Learning Objectives
After completing Chapter 7, the student will be able to:
7.1 Identify the nutrients involved in energy metabolism and the high-energy compound that captures the
7.2 Summarize the main steps in the energy metabolism of glucose, glycerol, fatty acids, and amino acids.
a. Describe how carbohydrates, proteins, and fats are used to meet the energy needs of the body.
7.4 Describe how alcohol disrupts metabolism and impairs health.
a. Discuss the term moderation in reference to alcohol consumption.
b. Explain how the body metabolizes alcohol.
c. Discuss the role of the liver in alcohol metabolism.
d. Discuss the short- and long-term effects of alcohol on health.
Assignments and Other Instructional Materials
The following ready-to-use assignments are available in this chapter of the instructor’s manual:
• Case Study 7: Excessive Alcohol Use
• Worksheet 7-1: Metabolism Exercises
1
• Worksheet 7-2: Anabolic or Catabolic?
2
Lecture Presentation Outline
4
Key to instructor resource annotations (shown to the right of or below outline topics):
TRA = Transparency acetates: 13e = 13th edition, 12e = 12th edition, 11e = 11th edition, 10e = 10th edition
Website = Available for download from book companion website: HN = student handout
IM = Included in this instructor’s manual: CS = case study, WS = worksheet, CA = classroom activity
1
Worksheets 7-1 and 7-3 contributed by Daryle Wane.
2
Worksheet 7-2 and Handout 7-1 contributed by Sharon Rady Rolfes
3
Contributed by Carrie King.
4
Contributed by Melissa Langone.
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I. Chemical Reactions in the Body – Explain the following:
A. The Site of Metabolic Reactions—Cells – Metabolic reactions take place inside of cells
(Figure 7-1) 10e TRA 69
II. Breaking Down Nutrients for Energy (Figure 7-5) 12e TRA 15; IM CA 7-1, 7-2
A. Glucose IM WS 7-3
1. Glucose-to-Pyruvate – Glycolysis (Figure 7-6) 11e TRA 16
2. Pyruvate’s Options—Anaerobic or Aerobic
a. Anaerobic – lactate
4. Pyruvate-to-Acetyl CoA (Aerobic) – Is irreversible (Figures 7-8, 7-9, and 7-10) 10e TRA 73, 74
B. Glycerol and Fatty Acids IM HN 7-1
1. Glycerol-to-Pyruvate – Conversion of glycerol to pyruvate
C. Amino Acids (Figure 7-13) 10e TRA 77
1. Amino Acid Deamination
2. Amino Acid Pathways
E. The Final Steps of Energy Metabolism
1. The TCA Cycle – The TCA cycle contains a 4-carbon compound called oxaloacetate that has a critical
role (Figures 7-14 and 7-15) 11e TRA 17
III. Feasting and Fasting
A. Feasting—Excess Energy 10e TRA 83
1. Excess Protein – Is converted to fat but this is inefficient and indirect
2. Excess Carbohydrate – Is converted to fat but this is inefficient and indirect.
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C. Fasting—Inadequate Energy 10e TRA 85
1. Adaptation: Making Glucose – Produced from some amino acids (from proteins) and glycerol (from
triglycerides)
2. Adaptation: Creating an Alternate Fuel 10e TRA 86
a. The shift to ketosis occurs when the brain becomes fueled by ketone bodies
3. Adaptation: Conserving Energy – Symptoms of starvation:
a. Muscle wasting
1. Result in changes in metabolism similar to what occurs during fasting
2. Ketones will be present in the urine when glycogen depletion has occurred
3. When a dieter returns to a well-balanced diet, the body will retain depleted nutrients
IV. Highlight: Alcohol in the Body
A. Alcohol in Beverages (Figure H7-1)
1. Beer, wine, and distilled liquor (hard liquor)
2. Alcohol behaves like a drug
3. Moderation of drinks
a. 5 ounces of wine
1. In the GI Tract
a. Quickly absorbed
2. In the Liver (Figures H7-2 and H7-3) 10e TRA 87
a.. Accumulation of fatty acids
b. Alcohol dehydrogenase breaks down alcohol to acetaldehyde
3. In the Brain (Figure H7-4) – Alcohol acts as a narcotic, anesthetizes pain 11e TRA 18
C. Alcohol’s Damage
1. Dehydration – Alcohol suppresses antidiuretic hormone (ADH), resulting in the loss of body water
2. Malnutrition Website HN 7-2
a. Heavy drinkers may have inadequate food intake.
3. Short-Term Effects
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4. Long-Term Effects
a. Abuse during pregnancy
b. Third leading cause of preventable death
c. Health effects of heavy alcohol consumption
1. Arthritis
2. Cancer
3. Fetal alcohol syndrome
4. Heart disease
13. Psychological disturbances
D. Personal Strategies
1. Serve and consume nonalcoholic beverages
2. Drink slowly and consume alcohol moderately
3. Do not drive
Case Study 7: Excessive Alcohol Use
5
Steve Quintana is a 52-year-old Hispanic male with a family history of alcoholism. He is 6 feet 1 inch tall and
weighs 238 pounds, with much of his excess weight around his middle. He considers himself a social drinker
although he has had two arrests for driving under the influence of alcohol. He recently has been diagnosed with
diabetes and takes an oral medication to control his blood glucose. He also has high cholesterol and has recently
started on a lipid-lowering medication. Recent tests have revealed Steve has fatty liver, which concerns him. He also
reports having occasional low blood glucose (hypoglycemia) and feeling shaky and dizzy.
1. From information in this chapter, explain how Steve’s alcohol intake may be a factor in his diagnosis of fatty
liver.
2. What might help explain Steve’s low blood sugar reactions?
3. According to Table H7-5, even if Steve eats a balanced diet, what nutrients may not be well absorbed if he
continues to drink excessively?
4. Explain why Steve may be at risk for a deficiency of the B vitamins folate and thiamin. What might be a
reasonable recommendation to reduce this risk?
5. How would you address Steve’s concern about his fatty liver in a way that may encourage him to seek help in
abstaining from alcohol?
6. List at least 3 practical tips you would give to people who only drink alcohol occasionally and who want to stay
within current recommendations for health and safety.
Answer Key
1. Alcohol is broken down in the liver in preference over fatty acids, which then accumulate. Alcohol also
permanently changes the structure of liver cells, which impairs the liver’s ability to metabolize fats and can lead
to fatty liver.
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Suggested Classroom Activities
To teach metabolism well—that is, to teach it so that students do not try to memorize fragments of it blindly but
become intrigued with it, feel comfortable with it, and really understand it—is a challenge. It helps when you are
enthused about the subject. It also helps to have your objectives clearly in mind, and not to be unrealistically
ambitious. Do you want students to memorize and spit back all of the TCA cycle intermediates with their structures,
or do you want them to be able to tell you in words what kinds of transformations can occur among amino acids,
fatty acids, and glucose? Offer as much as students are able to assimilate in the available time. It usually doesn’t pay
to get into the details of the TCA cycle at the beginning level; too few gain any real understanding.
Ask students to consider a car having a manual transmission with only two gears: first and high. First gear is
beneficial for rapid acceleration. If you do not shift out of first gear, the car will no longer accelerate, and it will use
gasoline very inefficiently. You must shift into high gear to keep the car running efficiently at a higher speed.
Human beings obtain energy from two analogous processes: glycolysis and the TCA cycle. Anaerobic glycolysis
serves the need for quick energy to accomplish an intense activity for a short duration of time. For endurance
activities, additional energy must be obtained from the TCA cycle. Explain that the choice of activity determines the
proportions of fat and glucose burned during the activity.
Energy
Obtained
Measure of
Energy
Advantage
Disadvantage
Car
First gear
Miles/gallon
Quick acceleration
Can only be used for a few seconds
of acceleration
Human beings
Glycolysis
(anaerobic)
ATP
Quick, intense muscle
activity
Can only be used for a few seconds
as lactic acid is produced
Car
High gear
Miles/gallon
Used to sustain desired
velocity over maximum
amount of time
Depends on rate of oxygen delivery
to fuel source; better tuned engines
achieve maximum miles/gallon
Human beings
TCA cycle
(aerobic)
ATP
Used to sustain desired
amount of muscle activity
over maximum amount of
time
Depends on rate of oxygen delivery
to fuel source; better conditioning
improves rate of oxygen delivery
Classroom Activity 7-2: Obtain Feedback Regarding Understanding of Metabolism
Objective: Review and clarification Class size: Any
Instructions: Chapter 7 is one of the most challenging chapters in the text. Asking for feedback regarding the
concepts that were grasped and others that were less understood can provide an excellent baseline regarding areas
that need clarification for the subsequent class. At the end of class, students are asked to anonymously provide
feedback on the day’s lesson. Students are asked to respond to two or three short questions that can vary in format
122
and emphasis. Two common questions are: “What did you learn during this class?” and “What was least
understood?”
In addition to providing valuable feedback for the instructor, it challenges students to evaluate their own learning.
Study Card 7 Answer Key
1. Metabolism is the sum total of all the chemical reactions that go on in living cells. Energy metabolism includes
2. Coenzymes are complex organic molecules, many of which have B vitamins as part of their structures, that
work with enzymes to facilitate the enzymes’ activity. Without its coenzyme, an enzyme cannot function.
5. The 4 basic units derived from foods are glucose (6 carbons), glycerol (3 carbons), fatty acids (usually an even
number of carbons, often 16 or 18), and amino acids (2, 3, or more carbons).
6. Aerobic and anaerobic metabolism consist of oxygen-requiring and non-oxygen-requiring reactions,
respectively. Insufficient oxygen affects metabolism by forcing the body to rely more on anaerobic pathways
7. Before entering the metabolic pathways, amino acids are deaminated (that is, they lose their nitrogen-containing
14. In an effort to conserve body tissues for as long as possible, the hormones of fasting slow metabolism. During
fasting, the body can use its stores of fat to furnish most of its cells with energy, but the red blood cells are
completely dependent on glucose, and the brain and nerves prefer energy in the form of glucose. Glycerol and
15. Fat loss is the reduction in the body’s triglyceride stores from adipose tissue that results when energy intake is
inadequate and the body relies on fat stores to fuel body cells. Weight loss, on the other hand, can represent the
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Critical Thinking Questions
7
1. Describe how the body uses physiological mechanisms to control energy metabolism. What pathway is shared
by the macronutrients to help facilitate energy generation?
2. The liver is described as the “metabolic workhorse” of the body in that it facilitates metabolic processes for both
macro- and micronutrients. Provide a brief description of the significant roles that the liver plays with regard to
nutrient metabolism.
3. How does oxygen influence energy metabolism in the body?
4. Given that lipids are the most concentrated energy source based on mass (1 gram of fat provides 9 kcalories),
why are they not recommended to be the most significant dietary energy source for the body?
5. It has long been known that a minimum amount of carbohydrates must be present in the diet to spare protein. In
terms of energy metabolism, why is it also critical that a minimum number of carbohydrates be present to
facilitate energy metabolism?
6. If one does not consume an adequate mix of recommended nutrients (protein, lipids, and carbohydrate), how
will this affect energy metabolism and weight status?
Answer Key
1. Through a complex series of chemical reactions the body attempts to reach homeostasis. Food is broken down
into nutrient components so that energy can be generated to support cellular activities. Anabolic pathways
require energy, whereas catabolic pathways release energy. Utilizing this interplay of energy balance, cells in
the body participate in a series of chemical reactions facilitated by nutrient breakdown products, enzymes, and
2. Protein: Based on consumption, the liver manufactures non-essential amino acids and/or degrades proteins into
their constituent amino acids or converts them to glucose and lipids when in excess. The degradation process
produces ammonia, which the liver converts into urea for elimination via the renal system.
3. The presence and/or absence of oxygen in the body facilitates different chemical reactions in the body. Oxygen
as a driving force affects acid/base balance, which helps to maintain pH levels in the body. The body’s pH
status effectively either facilitates or turns off a particular reaction. In the presence of oxygen, this is called
4. Even though fats are more concentrated energy sources as compared to carbohydrates and protein, this fact does
not make them more readily available for energy retrieval. The major dietary lipid unit is triglycerides. The
5. Carbohydrates provide the main fuel of the body: glucose. This is a known fact. However, ingestion of
carbohydrates is also critical to help in the formation and regeneration of oxaloacetate in the TCA cycle.
6. Nutrient intake in the recommended proportions supports effective energy nutrient breakdown in the body.
Whereas excesses in protein and carbohydrates increase oxidation processes in the body, an excess of dietary fat
IM Worksheet Answer Key
Worksheet 7-1: Metabolism Exercises
Worksheet 7-2: Anabolic or Catabolic?
Worksheet 7-3: Fat and Carbohydrate Metabolism (Internet Exercise)
Worksheet 7-4: Blood Alcohol Levels
1-3. Answers will vary based on the individual’s weight.
Worksheet 7-5: Chapter 7 Crossword Puzzle
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Worksheet 7-1: Metabolism Exercises
Indicate whether each of the following reactions is anabolic or catabolic by circling the appropriate word:
Reaction Type of Reaction
1. Glucose + glucose → glycogen Anabolic Catabolic
2. C6H12O6 + 6H2O → 6CO2 + 6H2O Anabolic Catabolic
3. AB → A + B Anabolic Catabolic
8. Oxidation reaction Anabolic Catabolic
9. Muscle tissue breakdown → release of amino acids Anabolic Catabolic
10. Adipose tissue formed from fatty acids Anabolic Catabolic
11. A-OH + H-B → AB + HOH Anabolic Catabolic
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Worksheet 7-2: Anabolic or Catabolic?
Metabolism explains how the cells in the body use nutrients to meet its needs. Cells may start with small,
simple compounds and use them as building blocks to form larger, more complex structures (anabolism).
These anabolic reactions involve doing work and so require energy. Alternatively, cells may break down
large compounds into smaller ones (catabolism). Catabolic reactions usually release energy. Determine
whether the following reactions are anabolic or catabolic.
Anabolic
Catabolic
1. A cracker becomes glucose.
2. Glucose becomes glycogen.
3. You consume more energy than your body expends.
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Worksheet 7-3: Fat and Carbohydrate Metabolism (Internet Exercise)
1. Protein, carbohydrates, and fat are used in the body as the main energy sources.
2. A larger person requires more metabolic intake than a smaller person to sustain body functions.
3. In order to sustain itself from a metabolic standpoint, the body exhibits metabolic flexibility.
4. Which statement reflects the situation within the body in a fed state, after one has eaten a meal?
a. Decreased insulin and fat use and increased carbohydrate use
b. Decreased carbohydrate and fat use and increased insulin
c. Increased insulin and fat use and decreased carbohydrate
d. Increased insulin and carbohydrate use and decreased fat use
5. Which statement reflects the situation within the body in a fasting state?
6. Which statement reflects the situation within the body during performance of vigorous exercise?
7. Which statement provides the best explanation of the pie charts shown in the video?
a. The greatest percentage of carbohydrate use is found in the after-exercise state.
b. There is a proportional increase in fat usage seen between the fed state and vigorous exercise state.
c. The percentage of fat use appears to be consistent between the fed state and vigorous exercise state.
d. Smaller amounts of carbohydrates are used in the fed state and vigorous exercise state.
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Worksheet 7-4: Blood Alcohol Levels
Use the calculator to complete the table below based on your weight (choose the weight closest to yours from the
list). Select one type of drink from the list on the website, and use that same type of drink for each calculation. If
you drink, choose the beverage you like best or consume most often. Use 3 hours as the time period. Pay attention to
the description of your theoretical state (e.g., “possible impairment”) as well as your BAC.
Type of drink selected: _____________________________________________
Number of drinks
Blood alcohol concentration
1
2
Reflect on this information, and answer the following questions.
1. What did the website predict your state of alertness would be after 4 drinks? after 6? after 8?
2. After how many drinks did it predict your BAC would reach or exceed the legal limit for driving, 0.08%?
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Worksheet 7-5: Chapter 7 Crossword Puzzle
1
2
3
4
5
6
7
8
9
10
11
Across:
Down:
3. The number of _____ molecules relates to the
amount of energy a nutrient can provide.
8. Referred to as the sum of all chemical reactions in
living cells
11. Fatty acids cannot be converted to _____ so they
cannot generate glucose.
2. Carbohydrates, fat, and protein are referred to as
_____ nutrients.
5. Processes that occur without oxygen
7. Harmful effect of excessive alcohol intake that can
kcalories per gram
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Handout 7-1: The Carbons of a Typical Triglyceride
