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Chapter 5 – The Lipids: Triglycerides, Phospholipids, and Sterols
Learning Objectives
After completing Chapter 5, the student will be able to:
1. Describe the structure of a fatty acid and the effects of chain length and saturation on the properties of the fat.
2. Describe the triglyceride.
3. List and describe the three types of fatty acids found in foods.
4. Explain the structure of the omega-3 and -6 fatty acids.
5. Explain the roles of phospholipids and sterols in foods and in the body.
6. Trace the digestion of lipids including identification of enzymes needed and the role of bile.
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 5-1: Trans Fat1
Other instructional materials in this chapter of the instructor’s manual include:
• Answer key for How To (pp. 156, 159, 161) activities
• Classroom activities
• Worksheet answer keys (as appropriate)
• Handout 5-1: How to Modify a Recipe—Lasagna4
• New! Handout 5-2: Cholesterol in Selected Foods
Lecture Presentation Outline5
“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
Website = Available for download from book companion website: HN = student handout
I. The Chemist’s View of Fatty Acids and Triglycerides
The class of nutrients known as lipids includes triglycerides (fats and oils), phospholipids, and sterols. Most
are triglycerides with glycerol backbones and three fatty acids attached. Fatty acids vary in carbon chain
lengths, degree of unsaturation, and number of double bonds. Saturation affects the physical characteristics of
the fat and its storage properties. Trans-fatty acids, which are altered, have the same negative health effects as
saturated fatty acids.
A. Fatty Acids
1. The Length of the Carbon Chain
2. The Degree of Unsaturation
a. Saturated fatty acids carry the maximum possible number of hydrogen atoms. When most of the
fatty acids are saturated it is called a saturated fat. 10e TRA 40
b. Unsaturated fatty acids lack hydrogen atoms and have at least one double bond. The double
bond is considered the point of unsaturation.
1. Monounsaturated fatty acids lack two hydrogen atoms and have one double bond. When
3. The Location of Double Bonds 10e TRA 43
a. The omega number refers to the position of the first double bond.
b. An omega-3 fatty acid has the location of the double bond in the third position. An example is
linolenic acid.
B. Triglycerides are lipids with three fatty acids attached to a glycerol. 10e TRA 44, 45
C. Degree of Unsaturation Revisited 12e TRA 10; 10e TRA 46
1. Firmness
a. Saturated fats are solid at room temperature.
2. Stability
a. Saturated fat is more resistant to oxidation.
b. Monounsaturated fat is slightly less susceptible to spoilage.
3. Hydrogenation 10e TRA 47
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a. Protects against oxidation, therefore prolonging shelf life.
b. Alters texture.
4. Trans-Fatty Acids 10e TRA 48; IM WS 5-1, CA 5-5, CI 5.3
a. Act like saturated fats in the body.
II. The Chemist’s View of Phospholipids and Sterols
Phospholipids and sterols have unique chemical structures that allow them to have unique roles in the body.
Sterols have a multiple-ring structure.
A. Phospholipids
1. Phospholipids in Foods 10e TRA 49
a. Phospholipids contain glycerol, two fatty acids and a phosphate group with a molecule of choline.
2. Roles of Phospholipids
a. Enable transport of lipids across cell membranes.
B. Sterols – A well-known sterol is cholesterol.
1. Sterols in Foods 10e TRA 50
2. Roles of Sterols
a. Starting material for bile acids, sex hormones, adrenal hormones, and vitamin D.
b. Structural component of cell membranes.
III. Digestion, Absorption, and Transport of Lipids
Special arrangements are made in the digestion of lipids. This is due to the hydrophobic nature of lipids. Lipids
tend to separate from the watery fluids of digestion. Digestive enzymes are hydrophilic, or water loving. Bile
from the liver emulsifies lipids. Enzymes are then able to break down lipids to monoglycerides and fatty acids.
A. Lipid Digestion
1. In the mouth, the salivary glands release lingual lipase.
3. In the Small Intestine 10e TRA 51, 52
a. Cholecystokinin (CCK) signals the gallbladder to release bile.
b. Pancreatic and intestinal enzymes hydrolyze lipids to monoglycerides and fatty acids.
B. Lipid Absorption 10e TRA 53
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1. Glycerol and short- and medium-chain fatty acids diffuse and are absorbed directly into the
C. Lipid transport is made possible by a group of vehicles known as lipoproteins.
10e TRA 54, 55, 56; 12e TRA 11
1. Chylomicrons
a. Largest of the lipoproteins.
c. Get smaller as triglyceride portion is removed by the cells.
2. VLDL (Very-Low-Density Lipoproteins)
a. Composed primarily of triglycerides.
b. Made by the liver.
3. LDL (Low-Density Lipoproteins)
4. HDL (High-Density Lipoproteins)
5. Health Implications
a. High LDL is associated with higher risk of heart attack and is known as “bad” cholesterol.
1. Weight control.
2. Replace saturated fat with monounsaturated fat and polyunsaturated fat in the diet.
3. Soluble fibers.
d. Genes influence lipoprotein activity.
IV. Lipids in the Body
The triglycerides have important roles in the body. Essential fatty acids also play important roles. The body can
store unlimited amounts of fat when fat is consumed in excess. The liver can also convert excess carbohydrate
and protein to fat. The body needs carbohydrate to break down fat efficiently. Inefficient breakdown of fat
forms ketone bodies.
A. Roles of Triglycerides 10e TRA 57
1. A source of energy for the cells.
2. Provide more energy than carbohydrates or proteins.
B. Essential Fatty Acids – cannot be made by the body.
1. Linoleic Acid and the Omega-6 Family
2. Linolenic Acid and the Omega-3 Family
3. Eicosanoids
a. Made from arachidonic acid and EPA.
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b. Like hormones but have different effects on different cells.
c. Include prostaglandins, thromboxanes, and leukotrienes.
4. Fatty Acid Deficiencies
C. A Preview of Lipid Metabolism
1. Storing Fat as Fat
2. Using Fat for Energy
a. Hormone-sensitive lipase inside the adipose cells hydrolyzes triglycerides when needed for
energy.
V. Health Effects and Recommended Intakes of Lipids
High intakes of saturated fat and trans fat and high blood LDL cholesterol are related to increased risk for heart
disease. Omega-3 fatty acids in the diet appear to have a protective effect.
A. Health Effects of Lipids PL V “Cholesterol-Lowering Diet”
1. Blood lipid profile IM CI 5.6
a. Reveals concentrations of lipids in the blood
b. Desirable levels
1. Total cholesterol 200 mg/dL
2. Heart Disease IM CI 5.7, 5.8
a. Elevated blood cholesterol is a risk factor for cardiovascular disease.
3. Risks from Saturated Fats
a. Saturated fat in the diet raises LDL cholesterol, which increases risk of heart disease.
4. Risks from Trans Fats
a. Trans-fatty acids in the diet increase LDL cholesterol and decrease HDL cholesterol.
5. Risks from Cholesterol
6. Benefits from Monounsaturated Fats and Polyunsaturated Fats
a. Replacing saturated fat and trans fat with monounsaturated fat and polyunsaturated fat is the most
effective dietary strategy in preventing heart disease.
7. Benefits from Omega-3 Fats
a. Beneficial effects in reducing risk of heart disease and stroke, supporting the immune system, and
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b. Food sources include vegetable oils (canola, soybean, and flaxseed), walnuts and flaxseeds, and
fatty fish (mackerel, salmon, and sardines).
1. Need to avoid fish with high levels of mercury.
8. Omega-6 to Omega-3 Ratio
9. Cancer
a. Dietary fat has an association with risks for some types of cancer, but it is not as strong as the link
10. Obesity can be a consequence of high-fat, high-kcalorie diets in excess of energy needs.
B. Recommended Intakes of Fat IM WS 5-5, CA 5–4, CI 5.1, 5.2
1. The DRI and the 2005 Dietary Guidelines recommend fat at 20%-35% of energy intake (400-700
kcalories of a 2,000-kcalorie diet).
3. 2005 Dietary Guidelines suggest choosing a diet low in saturated fat and cholesterol and moderate in
total fat.
4. Daily Values
6. Too little fat can be detrimental to health.
C. From Guidelines to Groceries IM WS 5-3, HN 5-1, CA 5-2, 5-3, CI 5.5
1. Very lean and lean options of meats and meat alternates should be chosen.
2. Choose fat-free and low-fat milks and milk products.
3. Choose a wide variety of vegetables, fruits, and whole grains.
some consumers.
7. Read Food Labels
a. Provide information on fat grams and % Daily Values.
b. % Daily Values are not the same as % of kcalories from fat.
VI. Highlight: High-Fat Foods—Friend or Foe? IM CI Highlight
There are many relationships between the kinds of fat in the diet and their roles in supporting or harming health.
It is complex. Translating the research from general recommendations into specific recommendations is
challenging.
A. Guidelines for Fat Intake
1. It is recommended that individuals replace “bad” fats with “good” fats.
B. High-Fat Foods and Heart Health PL V “Heart–Healthy Habits for Women”; 11e TRA 14
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1. Cook with Olive Oil
2. Nibble on Nuts
3. Feast on Fish
a. Rich in long-chain omega-3 polyunsaturated fatty acids.
C. High-Fat Foods and Heart Disease
1. Limit Fatty Meats, Milk Products, and Tropical Oils
2. Limit Hydrogenated Foods
D. The Mediterranean Diet
1. Links with good health but may not be the only factor.
E. Conclusion
1. Saturated fat and trans fat are poor for heart health.
2. Unsaturated fat in moderation is good for heart health.
Case Study6
1. What factors may be contribute to Dave’s elevated cholesterol and triglyceride levels?
2. Identify the sources of saturated fat in Dave’s diet. What are some changes he could make to lower his intake of
saturated fat from these foods?
3. What general guidance pertaining to the source and firmness of different types of fat would help him identify
foods that contained healthier unsaturated fats in his diet?
Answer Key
1. Genetics (family history), alcohol consumption, diet high in saturated fat, inactivity.
2. Butter and cheese. Eat these foods less often or in smaller amounts or substitute less saturated forms of fat such
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3. Choose vegetable-based fats that are liquid at room temperature such as vegetable oils more often than animal–
based fats that are solid at room temperature such as butter or lard.
5. Replace food sources of saturated fat with moderate amounts of fish, nuts, and olive oil. Do not exceed more
than 35 percent of daily calories from total fat intake. Decrease or eliminate alcohol. Exercise daily.
6. 2000 calories x 0.35 = 700 calories ÷ 9 calories per gram = 78 grams of fat per day.
Suggested Classroom Activities
Remember that, while they’re familiar to you, to a new student words such as glycerol, triglyceride, and lipoprotein
are a jumble of unfamiliar new terms. It takes time to assimilate this new information. It helps to define the terms
repeatedly as you lecture. To sustain motivation, interject information relevant to students and their personal lives.
Relate lipids to heart disease, cancer, obesity, and other subjects.
Classroom Activity 5-1: Chapter Opening Quiz
Objective: Introduction to chapter Class size: Any
Classroom Activity 5-2: Compare Energy Values of Food Prepared by Different Techniques
Key concept: Effect of food preparation method on fat content Class size: Any
Instructions: Instruct students to calculate and compare the kcalories in a baked, broiled, or steamed food versus the
same food after frying. Use the table of nutrient composition of foods and fast foods in the appropriate appendix of
the textbook.
Classroom Activity 5-3: How to Modify a Recipe7
Key concept: Strategies for cutting fat in recipe Class size: Any
Classroom Activity 5-4: Discussion of Changing Guidelines for Fat Intake
Object: Exploring beliefs about fat Class size: Any
Classroom Activity 5-5: Trans Fat Label Analysis
Key concept: Trans fat; reading food labels Class size: Any
Materials needed: Copy of Worksheet 5-1 for each student
Instructions: Trans fat has major health implications and food labels include information regarding this fat.
Distribute Worksheet 5-1 and have students complete the questions.
Classroom Activity 5-6: Review of Fats
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Instructions: Distribute Worksheet 5-2 and ask students to complete this questionnaire to see how much information
they have retained. All 10 statements are false.
How To “Try It” Activities Answer Key
How to Make Heart-Healthy Choices—by Food Group8
Type of milk (1 cup)
Whole
Reduced-fat
Low-fat
Nonfat
How to Calculate a Personal Daily Value from Fat
58 g fat per day
How to Understand “% Daily Value” and “% kCalories from Fat”
%DV for fat = 6%; % kcal from fat = 31%
Critical Thinking Questions9
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. Lipids are chemically classified into three different categories: triglycerides, phospholipids, and sterols. Discuss
the details of these three different categories and the role they play in our bodies and in the food industry.
Answer: Triglycerides: Triglycerides are the predominant category of lipids in the body. Triglycerides are
composed of one glycerol molecule and three fatty acids. The number of double bonds within the chain of
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Sterols are ring structures, for which sex hormones are an example as are vitamin D, a fat-soluble vitamin, and
bile acids. Cholesterol, a sterol itself, is the building block for all of these substances. Endogenous cholesterol
or cholesterol made by the body is sufficient to meet the body’s needs. There also exist plant sterol sources that
can be helpful in clearing excessive exogenous cholesterol from the body.
Overall, it is important to point out that lipids are chemically composed of oxygen, carbon, and hydrogen,
similar to carbohydrates. However, lipids provide twice the kcalories or energy of carbohydrates or proteins.
While lipids are typically viewed as “bad” in the diet, lipids are necessary as noted above for cell membrane
structure, composition of hormones, digestion and absorption of fat-soluble vitamins, blood clotting
2. As your text points out, lipids are hydrophobic, which could be problematic as regards their absorption.
However, lipid enzymes are hydrophilic, enhancing the ability for lipids to be digested and absorbed. Discuss
the variety of factors that are involved in the absorption and transport of lipids in the body. How can some of
these factors be confusing to the average health consumer?
Answer: One fascinating point cited in the text was that “on average from the food we eat, 50-100 grams of
triglycerides, and 4 to 8 grams of phospholipids and 200 to 350 milligrams of cholesterol” are processed by the
body. Think about how remarkable our bodies are to process all of these lipids in this challenging environment!
And then think about all the individuals that eat well beyond the “average”!! The result is a body always
working overtime.
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they change in character and density, depending on the individual diet, activity level, health status, genetics, etc.
Triglycerides, sterols, and phospholipids are distributed, stored, and picked up and as the lipoprotein goes about
its business it may become more or less dense.
The consumer often becomes confused by the various interchanging terms for lipoproteins. What is good and
what is bad cholesterol? Where do VLDL and LDL and HDL come into the picture with all of this? What about
the proportions between them? Is cholesterol in all foods?
3. Lipids have many important functions. Discuss what important roles lipids have in our bodies.
Answer: As noted earlier, lipids or fats (the terms are being used interchangeably) are very important in our
bodies. First, extra layers of fat in our bodies protect against extreme negative temperatures (cold). Many
distance swimmers that have attempted to swim the English Channel have added additional layers of fat to
protect themselves against the cold temperatures of the water as well as to provide them with energy during
4. Differentiate between all the various components in a blood lipid profile. Discuss how different types of lipids
can affect the blood lipid profile, and how diet and exercise habits can be modified to improve it.
Answer: Normal Blood Lipid Profile:
• Total cholesterol: Less than 200 mg/dL
• LDL cholesterol: Less than 100 mg/dL
Overall, to maintain the best cholesterol profile, a diet that is full of complex carbohydrates is best. This allows
for plenty of intake of soluble and insoluble fiber. Be sure to select plenty of fruits and vegetables and well as
legumes and nuts to provide for a valuable source of photochemicals. Choose low-fat meats, fish, and poultry as
well as legumes for protein sources. Select monounsaturated and polyunsaturated fatty acids for the diet and
stay away from saturated fats and trans fats when selecting food products, meats, and cooking products. Plenty
of exercise is important to help raise HDL levels that support cholesterol clearance from the body. These
activities should assist each client in maintaining the correct weight for their body type and frame.
5. It is clear that many Americans consume too much fat or too many lipids in their diets. This might be evidenced
by the high prevalence of obesity, average cholesterol and LDL levels, and dietary intake patterns of the
American consumer. There are individuals that become fearful of obesity because of the prevalence of such
statistics, and therefore select diets almost void of fats. (a) What might this type of diet look like, (b) what might
be the outcome of such a dietary pattern on the body’s physiology given the importance of fat, and (c) how
might you counsel clients to include lipids in their diets in a healthful manner?
Answer: (a) A diet that is totally void of fats would be a diet that is free of any processed foods, dairy products,
meats, poultry, nuts, and of course oils, etc. Clearly, whole food groups are being left out of such a diet, which
would result in the individual becoming deficient in many micronutrients as well as the macronutrient lipid.
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With regard to fat, while the body does not require a great deal of fat to function at its optimum, some fat in the
diet is important to support physiological functions. Fat is needed for the phospholipids in the cell membranes,
for the sterols that support hormone production, for the bile acids that break down fats for transport to body
tissues, and for the various other functions of fats such as insulation, energy supply, and metabolic functions
such as blood clotting, etc. Americans clearly eat too much fat, yet we must not forget that some fat is not a bad
thing for the body. It has many important activities to perform every minute of the day to keep us going!
6. Dietary fads are as plentiful as the choices of unprocessed foods we have to select and consume in our diets. Yet
neither selection appears to be winning weight-loss battle for the American consumer. In this Highlight, you,
the student, received a recap on the chapter on lipids and learned a bit about the Mediterranean diet. Do you feel
this diet might stand out from other diet trends in being able to accomplish healthy weight loss for the American
consumer? Why or why not? Support your opinion with literature citations.
Answer: This question does ask the student for their opinion, which may support the dietary program or not
support the dietary program. Primary literature review citations have been requested for their write-up, which is
important in helping the student to establish their professional work ethic as one centered on evidenced-based