The Lipids:
Triglycerides,
Phospholipids,
and Sterols
Chapter 5
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Introduction
• Poor health
• Too much fat
• Too little fat
• Too much of some kinds of fat
• Family of lipids
• Triglycerides
• Phospholipids
• Sterols
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Chemist’s View of Fatty Acids
and Triglycerides
• Energy provided per gram greater than
carbohydrates
• More carbons and hydrogens
• Preview of lipids
• Triglycerides: glycerol and three fatty acids
• Fatty acids: even number of carbons
• Saturated or unsaturated
• Omega-3 and omega-6 fatty acids
• 18-carbon polyunsaturated fatty acids
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Fatty Acids
• Methyl group at one end
• Acid group at other end
• Usually even number of carbons
• 18-carbon fatty acids abundant in food
• Saturations
• Saturated – full of hydrogens
• Unsaturated – missing hydrogens
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18-Carbon Fatty Acids
Name
Nu mb er o f
Carb o n
Ato ms
Nu mb er o f
Do u b le
Satu ration
Bo n d s
Co mmo n F ood So urces
S t earic ac id
18
0
S at urat ed
Mos t animal f ats
Oleic ac id
18
1
Monouns aturat ed
Oliv e and c anola oils
Linoleic ac id
18
2
P oly unsaturated
S unf lower, s afflower, c orn,
and s oy bean oils
Linolenic ac id
18
3
P oly unsaturated
S oy bean and c anola oils,
f lax seed, walnuts
NOTE: Chemists use a shorthand notation to describe fatty acids. The first number indicates the number of carbon atoms; the second, the
number of the double bonds. For example, the notation for stearic acid is 18:0.
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Bonds in the Fatty Acid Chain
• Double bonds
• Nearest the methyl end of the carbon chain
• Omega number represents location of the
closest double bond from methyl end
• Omega-3’s closest double bond is three carbons
away from methyl end
• Linolenic acid
• Monounsaturated fatty acids
• Omega-9 groups
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Omega-3 and Omega-6 Fatty
Acids Compared
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Triglycerides
• Three fatty acids attached
to a glycerol
• Formed via series of
condensation reactions
• Usually contain mixture of
fatty acids
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Condensation of Glycerol and
Fatty Acids to Form a Triglyceride
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Characteristics of Solid Fats
and Oils
• Firmness
• Polyunsaturated fats tend to be liquid at room
temperature
• Saturated fats tend to be solid
• Length of carbon chain influences degree of
firmness
• Stability
• Fats spoil when exposed to oxygen
• Polyunsaturated fats spoil most readily
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Diagram of Saturated and
Unsaturated Fatty Acids Compared
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Fatty Acid Composition of
Common Food Fats
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Hydrogenation
•
•
•
•
Protects against oxidation
Makes liquid oils more solid
Partial hydrogenation most common
Trans-fatty acids
• Configurations – cis and trans
• Relatively few natural sources of trans fats
• Similarity to other types of fat
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Illustration of Hydrogenation
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Cis- and Trans-Fatty Acids
Compared
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Phospholipids
•
•
•
•
•
Solubility in fat and water
Emulsifiers in food industry
Lecithin is best-known
Food sources
Roles
• Part of cell membranes
• Emulsifiers
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Lecithin
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Sterols
• Food sources
• Cholesterol
• Plant sterols
• Roles of sterols
• Made in the body
• Structural component of
cell membranes
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Lipid Digestion
• Fats are hydrophobic
• Digestive enzymes are hydrophilic
• Goal of fat digestion
• Dismantle triglycerides
• Monoglycerides, fatty acids, and glycerol
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Fat Digestion in the GI Tract
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The Beginning of Fat Digestion
• Mouth
• Lingual lipase plays role in fat digestion in infants
• Stomach
• Strong muscle contractions
• Gastric lipase
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Lipid Digestion in the
Small Intestine
• Cholecystokinin (CCK)
• Gall bladder releases bile
• Bile acts as emulsifier
• Pancreatic lipase
• Hydrolysis
• Triglycerides and phospholipids
• Bile routes
• Effect on blood cholesterol levels
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Emulsification of Fat by Bile
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Fat
Watery GI
juices
Enzymes
In the stomach,
the fat and
watery GI juices
tend to separate.
The enzymes in
the GI juices
can’t get at the
fat.
Fat
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relationship ID rId5 was
not found in the file.
Bile
Emulsified
fat
Enzyme
The image part
with
relationship ID rId5 was
not found in the file.
Emulsified
fat
Emulsified
fat
When fat enters
the small intestine,
the gallbladder
secretes bile. Bile
has an affinity for
both fat and water,
so it can bring the
fat into the water.
Bile’s emulsifying
action converts
large fat globules
into small droplets
that repel each
other.
After
emulsification,
more fat is
exposed to the
enzymes, making
fat digestion more
efficient.
Stepped ArtEmulsification of fat by bile
Hydrolysis of a Triglyceride
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Enterohepatic Circulation
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In the gallbladder,
bile is stored.
In the liver,
bile is
made from
cholesterol.
In the small intestine,
bile emulsifies fats.
In the colon, bile that has
been trapped by soluble
fibers is lost in feces.
Stepped ArtEnterohepatic Circulation
Lipid Absorption
• Directly into bloodstream
• Glycerol and short- and medium-chain fatty acids
• Lymphatic system
• Micelles diffuse into intestinal cells
• Reassembled into triglycerides
• Packed with proteins into transport vehicles called
chylomicrons
• Bypass liver at first
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Absorption of Fat
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Lipid Transport
• Four main types of lipoproteins
• Chylomicrons
• Largest and least dense
• Transport diet-derived lipids
• Liver removes remnants from blood
• Very-low-density lipoproteins (VLDL)
• Made in the liver
• Proportion of lipids shifts
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Lipoprotein Types
• Low-density lipoproteins (LDL)
• Cell needs
• Liver regulation
• High-density lipoproteins (HDL)
• Remove cholesterol from cells
• Carry cholesterol to liver for recycling
• Anti-inflammatory properties
• Health implications
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Sizes and Compositions of the
Lipoproteins
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Lipid Transport via
Lipoproteins
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Roles of Triglycerides
• Provide the cells with energy
• Virtually unlimited ability to store fat energy
• Adipose tissue stores body fat
• Secretes hormones (adipokines)
• Other uses of fat in the body
•
•
•
•
Skin insulation
Shock absorption
Cell membrane material
Cell signaling pathways
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An Adipose Cell
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Essential Fatty Acids
• Must be supplied by
the diet
• Linoleic acid
• Linolenic acid
• Can be used to make
other fatty acids
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Omega-6 and Omega-3 Fatty
Acids
• Linoleic acid – Omega-6 fatty acid
• Sources: vegetable oils and meats
• Linolenic acid – Omega-3 fatty acid
• Cannot be made in the body
• Must be supplied by food
• DHA
• EPA
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Eicosanoids
• Eicosanoids
• “Hormonelike”
• Health benefits
• Omega-6 to Omega-3 ratio
• Fatty acid deficiencies
• Rare in the United States and Canada
• Symptoms
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A Preview of Lipid Metabolism
• Adipose cells store fat after meals
• Lipoprotein lipase
• Hydrolyzes triglycerides
• Triglycerides reassembled inside adipose cells
• Using fat for energy
• Fat supplies 60 percent of energy needs during
rest
• Energy deprivation
• Fasting: fat and lean protein tissue used for energy
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Health Effects of Saturated Fats,
Trans Fats, and Cholesterol
• Current American diet
• Excessive amounts of solid fats
• Blood lipid profile
• Heart disease
• Elevated LDL cholesterol a risk factor
• Saturated fats increase LDL cholesterol, promote
blood clotting
• Dietary choices
• Trans fats – increase LDL cholesterol
• Dietary cholesterol
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Fat Links to Cancer and Obesity
• Cancer
• Dietary fat and cancer risk
• Differs for various types of cancer
• Promotion rather than initiation of cancer
• Obesity
• Cutting fat from diet reduces kcalories
• Dietary recommendations
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Recommended Intakes of Saturated
Fat, Trans Fat, and Cholesterol
• DRI and Dietary Guidelines
• 20 to 35 percent of daily energy from fat
• Less than 10 percent of daily intake from
saturated fat
• As little trans fat as possible
• Less than 300 mg cholesterol
• Avoid getting too little fat
• Recommendation: one teaspoon of fat with every
meal
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Health Effects of Monounsaturated
and Polyunsaturated Fats
• Heart disease
• Replace saturated fats with
unsaturated fats
• Regular consumption of
omega-3 fatty acids
• Suppresses inflammation
• Cancer
• Omega-3 fatty acids from
food
• Supplements
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Replacing Saturated Fat
with Unsaturated Fat
Portion sizes have been adjusted so that each of these foods provides approximately 100 kcalories. Notice that
for a similar number of kcalories and grams of fat, the second choices offer less saturated fat and more
unsaturated fat.
…with these foods
Replace these foods…
Saturated Unsaturated Total
Fat (g)
Fat (g)
Fat (g)
Butter (1 tbs)
Bacon (2 slices)
Potato chips (10 chips)
Cheese (1 slice)
Steak (1'/2 0z)
Totals
Saturated Unsaturated Total
Fat (g)
Fat (g)
Fat (g)
7
4
11
Olive oil (1 tbs)
3
6
9
Sunflower seeds (2 tbs)
2
5
7
Mixed nuts (2 tbs)
4
4
8
Avocado (6 slices)
2
3
5
18
22
40
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Salmon (2 oz)
Totals
2
9
11
1
7
8
1
8
9
2
8
10
1
3
4
7
35
42
Recommended Intakes of Monoand Polyunsaturated Fats
• 20 to 35 percent of kcalories from fat
• Includes essential fatty acids
• AI have been established
• DRI
• Linoleic acid: 5-10% of daily energy
• Linolenic acid: 0.6-1.2% of daily energy
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Selecting Groceries
• Fat-soluble vitamins
• A, D, E, and K
• Flavor, texture, and palatability
• Protein foods
• Selections
• Milk and milk products
• Selections
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Cutting Fat Cuts kCalories and
Saturated Fat
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Grocery Choices
• Vegetables, fruits, and grains
• Lowers consumption of various fats in the diet
• Provides phytochemicals
• Solid fats and oils
• Fried and baked goods
• Choose wisely
• Unprocessed foods
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Food Labeling
• Total fat, saturated fat, trans fat, and
cholesterol
• Compare products
• Percent Daily Value versus percent kcalories
from fat
• Fat replacers
• Types
• Risks
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High-Fat Foods –
Friend or Foe?
Highlight 5
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Guidelines for Fat Intake
• Limit saturated fat and trans fat intake
• Moderate kcalories
• Enough fat for good health
• Not too much of the harmful fats
• DRI recommendations
• Compatible with low rates of disease
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High-Fat Foods and Heart
Health
• Olive oil
• Benefits for heart health
• Replace saturated fats
• Nuts
•
•
•
•
LDL cholesterol
Fat composition
Benefits for heart health
Cautious advice for dietary inclusion
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Fish
• Omega-3 fatty acids
• Benefits for heart health
• Environmental contaminants
• Farm raised versus wild
• Dietary recommendations
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High-Fat Foods and Heart
Disease
• Saturated fat the top dietary determinant of
LDL cholesterol
• Sources of saturated fat in the U.S.
• Meats
• Whole milk products
• Tropical oils
• Zero saturated fat is not possible
• Trans fat
• Limit hydrogenated foods
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Two Meals Compared
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The Mediterranean Diet
• Features of a traditional Mediterranean diet
•
•
•
•
•
Low in saturated fat
Very low in trans fat
Rich in monounsaturated and polyunsaturated fat
Rich in complex carbohydrate and fiber
Rich in nutrients and phytochemicals
• Benefits for heart disease risk
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Mediterranean Diet Pyramid
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