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HLTH 213
Lecture #3
Chapter 2
Nutrients: Ingestion to Energy Metabolism
Chapter Objectives
1. Describe the digestive system, its parts, and their general functions.
2. Explain the basic structure of carbohydrates and describe how they are digested, absorbed, transported,
and assimilated in the body.
3. Explain the basic structure of dietary fats and describe how they are digested, absorbed, transported, and
assimilated in the body.
4. Explain the basic structure or proteins and describe how they are digested, absorbed, transported, and
assimilated in the body.
5. Explain how minerals, vitamins, and water are absorbed and transported in the body.
6. Define energy metabolism and explain why understanding it is important.
7. Define energy and its basic forms.
8. Define adenosine triphosphate (ATP) and understand its role in the body.
9. Discuss the metabolic-factory concept of how cells make ATP.
10. Introduce the three energy systems, their characteristics, and the metabolic pathways associated with
each.
11. Discuss the metabolic pathways associated with the aerobic breakdown of carbohydrates.
12. Discuss the metabolic pathways associated with the aerobic breakdown of fats and proteins.
13. Explain how the energy systems work together to supply ATP during sport performance.
Chapter Outline
I. What happens to nutrients after they are ingested?
A. They enter the digestive tract but do not officially enter the body (Figure 2.1).
Author Note: Ask students what happens if a penny is swallowed.
B. Once food is placed in the mouth, the process of digestion begins.
C. Each region of the digestive tract serves a specific role (Figure 2.2).
II. How are carbohydrates digested, absorbed, transported, and assimilated in the body?
A. Carbohydrates are broken down into simple sugars during digestion.
B. Carbohydrate digestion involves the following:
1. Mastication
2. Enzymatic breakdown in the mouth (i.e., amylase) and small intestines (i.e., pancreatic
amylase, brush border disaccharides)
C. Absorption
1. Occurs primarily in the small intestine (i.e., jejunum)
2. Nutrients can be absorbed in the following ways:
a. Passive diffusion (no role in carbohydrate absorption)
b. Facilitated diffusion (fructose is absorbed this way)
c. Active transport (glucose is absorbed this way)
d. Endocytosis (no role in carbohydrate absorption)
D. Transport
1. Sugars are delivered in solution in the blood plasma.
E. Assimilation
1. Active transport into cells occurs via glucose transporters (i.e., GLUT1, GLUT4).
2. Carbohydrates can be stored as glycogen, converted to fat, or used for energy (see
Figure 2.9).
III. How are fats digested, absorbed, transported, and assimilated in the body?
A. Most dietary fats exist as triglycerides (Figure 2.10).
1. Glycerol backbone
2. Fatty acids (Figure 2.11)
a. Short (4 or fewer carbons)
b. Medium (6 to 10 carbons)
c. Long (12 or more carbons)
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B. Fat digestion involves the following (Figure 2.12):
1. Mastication
2. Emulsification
3. Enzymatic breakdown in the mouth (lingual lipase), stomach (gastric lipase), and small
intestines (pancreatic lipase)
C. Absorption (Figure 2.13)
1. Occurs in the small intestine
2. Passive diffusion is mode of absorption
D. Transport
1. Chylomicrons in the lymph (monoglycerides and long-chain fatty acids)
2. Blood plasma (short- and medium-chain fatty acids)
E. Assimilation
1. Short- and medium-chain fatty acids are absorbed by cells via passive diffusion.
2. Triglycerides in chylomicrons are acted on by lipoprotein lipase; released fatty acids
are absorbed via passive diffusion.
3. Once in cells, fats can be resynthesized into triglycerides or used for energy.
Author Note: Ask students to speculate how and where "fat-blocking" weight-loss compounds may disrupt
fat digestion and thus decrease calories available to the body.
IV. How are proteins digested, absorbed, transported, and assimilated in the body?
A. Proteins are composed of amino acids.
B. Protein digestion involves the following (Figure 2.15):
1. Mastication
2. Exposure to acids in stomach causing denaturation
3. Enzymatic activity in the small intestine (i.e., proteases, peptidases)
B. Absorption
1. Facilitated diffusion
2. Active transport (majority of amino acids)
C. Transport
1. Blood plasma
D. Assimilation
1. Enters cells via facilitated diffusion.
2. Once in cells, amino acids can be used to synthesize new structural proteins, enzymes,
hormones, or other nitrogen-containing compounds. (See protein synthesis, Figure 2.17.)
a. Transcription
b. Translation
3. They can also be used for energy if other sources of energy are low or energy demands
are high.
V. How are minerals, vitamins, and water absorbed and transported in the body?
A. These nutrients do not have to be broken into smaller units.
B. Digestion does help to release these nutrients from the foods ingested so that they can be
absorbed.
C. Water-soluble vitamins (B-complex and C) are absorbed, along with water, via passive
diffusion, primarily in the small intestine. They move freely throughout the body within the
watery fluids found inside and outside of cells.
D. Fat-soluble vitamins dissolve in digested fats of foods and are absorbed via passive diffusion in
the small intestine. They are transported via chylomicrons in lymph to the bloodstream where they
are then transported throughout body.
E. Minerals are absorbed via passive diffusion in the small and large intestines. The majority of
minerals are absorbed in the small intestine; Na, K, and Cl are absorbed in the large intestine. Like
water-soluble vitamins, they move freely throughout the body within the body fluids.
VI. What is energy metabolism and why is it important?
A. Energy metabolism is a foundational component of sports nutrition. Without knowledge of
energy metabolism and energy systems, the sports nutrition professional is severely disadvantaged
with regard to creating an individualized diet plan.
Author Note: Have the class come up with examples of why knowledge of energy metabolism would be
important to the sports nutrition professional.
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VII. What is energy?
A. Energy has no shape, no describable features, and no physical mass.
B. Energy is defined as the ability to perform work.
C. Energy exists in several forms: thermal, electrical, nuclear, chemical, mechanical, and radiant.
The form of energy that drives human metabolism is chemical energy.
VIII. What is the human body's source of chemical energy?
A. The energy currency of the body is adenosine triphosphate, or ATP. It provides energy for all
biological work (Figure 2.19).
B. When phosphate bonds in ATP are broken, energy is released and used by the body to perform
work (Figure 2.20).
IX. How do cells make ATP?
A. Cells possess enzymes and organelles (most notably mitochondria) that break down
macronutrients (i.e., carbohydrates, proteins, fats), releasing energy that can be captured to form
ATP. ATP can then be used to power cellular work/activity.
B. The capture, transfer, and use of energy within biological systems is known collectively as
“bioenergetics.”
X. What are the three energy systems?
A. Phosphagen System (Immediate Energy System)
1. Low-complexity process with essentially no lag time in supplying ATP
2. Very fast rate of production of ATP
3. Very limited capacity to make ATP
B. Anaerobic System
1. Slightly more complex process with short lag time in supplying increased demand for
ATP
2. Fast rate of production; runs a close second to phosphagen system
3. Limited capacity to make ATP
4. Results in the formation of lactic acid
C. Aerobic System
1. Highly complex process with long lag time relative to other two systems
2. Slow rate of production compared to the other energy systems; runs a distant third
3. Unlimited capacity to make ATP as long as oxygen is present; default energy system
the body relies on to survive
4. Results in formation of carbon dioxide and water
D. All three energy systems work together to meet the energy demands placed upon the body at
any point in time (Figure 2.25). At rest, the predominant energy system is the aerobic system.
XI. What pathways are associated with the aerobic breakdown of carbohydrates?
A. Metabolic pathways are sequences of reactions that are catalyzed by enzymes. Metabolic
pathways allow for the slow and controlled breakdown of foodstuffs so that energy can be
captured and used to form ATP.
B. Glycolysis: Breaks glucose into two pyruvate molecules. After glycolysis but before entering
into the next metabolic pathway, the pyruvate molecules are converted into acetyl CoA molecules.
C. Citric acid cycle (Figure 2.30): Strips hydrogen from entering acetyl CoA molecules.
D. Electron transport chain (Figure 2.31): Responsible for the stepwise transfer of hydrogens from
the citric acid cycle to oxygen, which results in the formation of water and ATP.
XII. What pathways are associated with the aerobic breakdown of fats and proteins?
A. Fats (Figure 2.28)
1. Beta-oxidation
2. Citric acid cycle
3. Electron transport chain
B. Proteins (Figure 2.28)
1. Deamination
2. Citric acid cycle
3. Electron transport chain
XIII. How do the energy systems work together to supply ATP during sport performance?
A. Sport participation places a continuum of energy demands on the body. The intensity and
duration of activities dictates the energy requirement. The three energy systems work together to
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meet those requirements (Figure 2.34). If the energy demands can't be met (i.e., metabolic
production of ATP can’t match activity demand), then the athlete fatigues and is no longer able to
continue at that intensity.
Author Note: Break the class into groups and give each group a different sport. Each group should think of
the activities involved in the sport and try to determine the role each energy system plays during those
activities. Then have the groups consider the overall total energy demands within that sport (i.e., all the
different activities combined) and determine which energy system is most influential in regards to
participating in that sport.
Chapter Discussion Questions
1. Assume that you are an insoluble fiber that has been ingested. What regions of the digestive system will
you pass through, what are the roles of each of those regions, and how many, if any, calories will you
provide the body? (pp. 28–29)
2. You are a starch that has been ingested. Describe the parts of the digestive tract you may pass through
and the digestive processes you experience in each region. Describe where and how you are absorbed
across the digestive tract lining. (pp. 29–33)
3. Discuss how fats are digested and absorbed in the digestive tract. (pp. 36–37)
4. Explain how proteins are constructed from individual amino acids within the cells. (pp. 43–44)
5. Explain why the following statement is not totally accurate: "Carbohydrates, fats, and proteins supply the
energy for exercise." (p. 46)
6. Discuss the metabolic pathways required to aerobically metabolize carbohydrates, fats and proteins.
Which, if any, of these pathways are common to all three foodstuffs? (p. 53, Figure 2.28)
7. Discuss the role of the aerobic energy system in sports that predominantly rely on the phosphagen and
anaerobic systems for successful performance. In other words, discuss why being in fairly good aerobic
shape might be beneficial to athletes involved in sports such as football that are considered to be “anaerobic
sports.” (pp. 57–58)
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