Chapter 5
The Lipids: Fats, Oils,
Phospholipids, and Sterols
Nutrition: Concepts & Controversies, 12e
Sizer/Whitney
Learning Objectives
 Discuss the reasons why a moderate intake
of lipids is an essential part of a healthy
diet.
 Compare and contrast the physical
properties and the sources of saturated,
polyunsaturated, and monounsaturated
fats.
Learning Objectives
 Describe how and where dietary lipids are
broken down and absorbed during
digestion and how they are transported
throughout the body.
 Describe the significance of the blood tests
for HDL and LDL cholesterol.
 Describe the roles of omega-3 and omega6 fatty acids in the body, and discuss which
may be too low in some people’s diets and
how they can increase their intakes.
Learning Objectives
 Justify the recommendation to eat fatty fish
instead of relying on fish oil supplements,
and discuss safety issues surrounding both
choices.
 Describe the information and structure of a
trans-fatty acid, and state ways in which
consumers may reduce their intakes.
Learning Objectives
 Develop a diet plan that provides enough of
the right kinds of fats within calorie limits.
 Discuss evidence for the benefits and
drawbacks of specific dietary fats in terms
of their potential effects on human health.
Introduction
 Diet moderate in fats
 Lipids are necessary and valuable
 Lipids can harm health
 Three classes of lipids
 Triglycerides
 Phospholipids
 Sterols
Usefulness of Fats in the Body
 Chief storage form of energy
 Provides most energy for body’s work
 Adipose tissue
 Secretes hormones
 Purposes of fat
 Shock absorbers, insulation, cell
membranes
 Fat-soluble substances
A Fat Cell
Muscle
tissue
Fat
tissue
Blood
capillaries
Fat
cell
Lipids enter
from blood
Lipids exit
to blood
Nucleus
Cell
membrane
Fig. 5.1, p. 151
Usefulness of Fats in Food
 People naturally
like high-fat foods
 Aromas
 Flavors
 Tenderness
 Satiety
Triglycerides: Fatty Acids and
Glycerol
 Triglycerides
 Glycerol backbone
 Three fatty acids
 Fatty acid
differences
 Chain length
 Saturation
 Animal species
make triglycerides
Glycerol
3 fatty acids
of differing
lengths
A triglyceride
formed from
1 glycol +
3 fatty acids
Fig. 5.3, p. 153
Saturated Versus Unsaturated
Fatty Acids
 Saturation
 Hydrogen atoms
 Levels of saturation
 Saturated
 Unsaturated
 Polyunsaturated
 Monounsaturated
Three Types of Fatty Acids
Saturated
Monounsaturated
Polyunsaturated
Point of
unsaturation
Points of
unsaturation
Fig. 5.4, p. 154
Saturated Versus Unsaturated
Fatty Acids
 Melting point
 More unsaturated,
more liquid
 Fat hardness
 Softer generally is
healthier
 Sources of fatty
acids
 Heart disease
Fatty Acid Composition of
Common Food Fats
Phospholipids and Sterols
 Phospholipids
 Glycerol, two fatty acids, and a phosphorus
molecule
 Soluble in water and fat
 Emulsifier
 Sterols
 Roles in the body
 Plant sterols
Digestion and Absorption of Fats
 Digestion
 Stomach
 Small intestine
 Bile
 Pancreas
Fat
Fat
Watery
digestive
juices
Enzyme
Bile compounds
Emulsified
fat
Emulsified
fat
Enzymes
In the stomach, the fat
and watery digestive
juices tend to separate.
Enzymes are in the water
and can’t get at the fat.
When fat enters the small
intestine, the gallbladder
secretes bile. Bile
compounds have an
affinity for both fat and
water, so it can bring the
fat into the water.
After emulsification, more
fat is exposed to the
enzymes, making fat
digestion more efficient.
Fig. 5.6, p. 157
Digestion and Absorption of Fats
 Absorption
 Fatty acids split from glycerol
 Fatty acids, phospholipids, and
monoglycerides
 Bile shuttles lipids across mucus layer
 Efficiency of absorption process
 Speed of digestion
The Process of Lipid Digestion
and Absorption
Esophagus
Pancreas
Stomach
Liver
1 In the mouth and stomach:
2
Little fat digestion takes place.
Small
intestine
2 In the small intestine:
Digestive enzymes accomplish most
fat digestion in the small intestine.
There, bile emulsifies fat, making it
available for enzyme action. The
enzymes cleave triglycerides into
free fatty acids, glycerol, and
monoglycerides.
3
Large intestine
(colon)
3 At the intestinal lining:
The parts are absorbed by intestinal
villi. Glycerol and short-chain fatty
acids enter directly into the
bloodstream.
4
Capillary
network
Lymph
The cells of the intestinal lining
4 convert large lipid fragments, such
as monoglycerides and long-chain
fatty acids back into triglycerides
and combine them with protein,
forming chylomicrons (a type of
lipoprotein) that travel in the lymph
vessels to the bloodstream.
Villi
Chylomicrons
Blood
vessels
5 In the large intestine:
A small amount of cholesterol
trapped in fiber exits with the feces
Lymph
to blood
5
Bloodstream
Fig. 5.7, p. 158
Transport of Fats
 Glycerol and shorter-chain fatty acids
 Bloodstream
 Larger lipids
 Protein carriers
 Released into lymph
 Chylomicrons
Storing and Using the Body’s Fat
 Body conserves fat molecules
 Fat depots
 Excess carbohydrate
 Call for energy
 Dismantle stored triglycerides
 Release fatty acids into blood
 Carbohydrate’s role
 How to use more fat for energy…
Glucose to Fat
Fatty acid
Glucose is
broken down
into fragments.
The fragments can
provide immediate
energy for the tissues.
Or, if the tissues need no
more energy, the fragments
can be reassembled, not
back to glucose but into
fatty acid chains.
Fig. 5.8, p. 159
Dietary Fat, Cholesterol, and
Health
 Heart and artery disease
 Saturated and trans fats
 Beneficial fats
 Cancer
 Diet high in saturated fats
 Obesity
 Overconsumption of calories
Recommendations for Lipid
Intakes
 Some fat in the diet is essential
 Healthy range of fat intakes
 DRI
 20 to 35 percent of daily energy
 Fats to keep low
 Essential fatty acids
Lipoproteins and Heart Disease
Risk
 Lipoprotein movement in the body
 Liver
 Types of lipoproteins
 Chylomicrons
 Very-low-density lipoproteins (VLDL)
 Low-density lipoproteins (LDL)
 High-density lipoproteins (HDL)
Lipoproteins
100
80
Protein
60
40
Cholesterol
20
Phospholipid
Triglyceride
0
LDL
(More lipid,
less protein)
Lower density
HDL
(Less lipid,
more protein)
Higher density
Fig. 5.9, p. 162
Phospholipid
Protein
Cholesterol
Triglyceride
A typical lipoprotein
Fig. 5.9, p. 162
Lipoproteins and Heart Disease
Risk
 LDL and HDL
difference
 Size and density
 Delivery and
scavenging
 Inflammation
 Heart attack risk
 Oxidation of LDL
 Phytochemicals
Food Cholesterol and Blood
Cholesterol
 Saturated and trans fats
 CVD risk indicators
 Dietary cholesterol
 Genetic inheritance
 Moderation is key
Recommendations Applied
 Heart disease
 Leading cause of death among Americans
 Lower LDL
 Dietary tactics
 Trim saturated and trans fats from diet
 Raise HDL
 Physical activity
 Benefits for heart health
Food Fat, Saturated Fat, and
Calories
Top Contributors of Saturated
Fats to the U.S. Diet
The Need for Essential Fatty
Acids
 Essential fatty acids
 Linoleic acid and
linolenic acid
 Functions
 Eicosanoids
 DRI recommendations
 Deficiencies
Omega-6 and Omega-3 Fatty
Acid Families
 Linoleic
 Omega-6 fatty acid
 Arachidonic acid
 Linolenic acid
 Omega-3 fatty acid
 DHA and EPA
 Heart disease
 Brain function and vision
 Inflammation
Fish Oil Intakes and
Cardiovascular Death Rates
Recommendations for Omega-3
Fatty Acid Intake
 Competition for metabolic enzymes
 Consumption levels
 Lacking omega-3 fatty acids
 Fish oil supplements
 Health concerns with fish oil supplements
 Omega-3 enriched foods
 Flaxseed
Food Sources of Omega-6 and
Omega-3 Fatty Acids
Seafood Safety – Balancing Risks
and Benefits
 Safe consumption levels
 Mercury
 Methylmercury
 Damage to the body
 Cooking methods of fish
 Benefits outweigh risks
Mercury in Fish Species
Effects of Processing on
Unsaturated Fats
 Hydrogenation
 Effects on fats
 Oxidation of unsaturated oils
 Hydrogenation of oils
 Benefits of hydrogenation
 Nutrient losses
 Alternatives to hydrogenation
Hydrogenation Yields Both
Saturated and Trans-Fatty Acids
Unsaturated fatty acid
Points of unsaturation are places on fatty acid chains where
hydrogen is missing. The bonds that would normally be
occupied by hydrogen in a saturated fatty acid are shared,
reluctantly, as a double bond between two carbons that both
carry a slightly negative charge.
Point of
unsaturation
Hydrogenated fatty acid (now fully saturated)
When a positively charged hydrogen is made
available to an unsaturated bond, it readily
accepts the hydrogen and, in the process,
becomes saturated. The fatty acid no longer
has a point of unsaturation.
Trans-fatty acid
The hydrogenation process also produces
some trans fatty acids. The trans fatty acid
retains its double bond but takes a twist
instead of becoming fully saturated. It
resembles a saturated fatty acid both in
shape and in its effects on health.
Fig. 5.14, p. 172
Effects of Processing on
Unsaturated Fats
 Trans-fatty acids
 Polyunsaturated fats
 Change in chemical structure
 Health effects
 LDL and HDL cholesterol
 Similarities with saturated fat
 Trans fat in foods
Fat in the Diet
 Essential fat
 20% of calories from unsaturated fats
 Visible vs. invisible fat
 Added fats
 Majority are invisible fats
Fat in the Diet
 Meat, poultry, fish, dried peas & beans,
eggs, & nuts
 Four categories for meat
 Limit intake to 5 to 7 ounces per day
 Choosing low-fat meats
 Ground turkey or chicken vs. beef
 Milk, yogurt, and cheese
 Foods not included in this category
 Grains
Calories, Fat, and Saturated Fat
in Cooked Ground Meat Patties
Lipids in Milk, Yogurt, and Cheese
Lipids in Bread, Cereal, Rice, and
Pasta
Defensive Dining
 Portion sizes
 In the grocery stores
 Fat replacers & artificial fats
 Olestra
 “Fat-free” options
 Cooking at home
Substitute Ingredients to Lower
Saturated Fat Intakes
Defensive Dining
 Use flavorful fats
 Choose unsaturated oils
 Revamp recipes
 Suggestions
 Find lower-fat fast foods
 Change your habits
Good Fats and Bad Fats –
Which are Which?
Controversy 5
Objectives to “Low-Fat”
Guidelines
 Problems with low-fat diets
 Groups who benefit from low-fat diets
 Mediterranean-type diets
 New guidelines
 Up to 35 percent of total calories
High-Fat Foods and Heart Health
 Olive oil
 Potential health
benefits
 Darker the better
(extra virgin)
 Canola oil
High-Fat Foods and Heart Health
 Mediterranean diet
 Whole foods
 Dietary focus
 Fish
 Nuts
 Walnuts
 Almonds
 Potential benefits
High-Fat Foods and Heart Health
 Butter or margarine
 Read labels
 Low saturated fat and trans fat levels
 Plant-enriched margarines
 Drawbacks
 Fats to avoid
 Choose carefully among high-fat foods
Impact of Change in Saturated Fatty
Acid Intake on Blood LDL Cholesterol
and Heart Disease Risk