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Chapter 5 Lecture
The Science of Nutrition
Third Edition
Lipids: Essential
Energy-Supplying
Nutrients
© 2014 Pearson Education, Inc.
What Are Lipids?
• Lipids
– Diverse group of molecules that are insoluble
in water
• Fats
– The lipid content of diets and foods
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What Are Lipids?
• Three types of lipids are found in foods and in
body cells and tissues:
– Triglycerides
– Phospholipids
– Sterols
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Triglycerides
• Triglycerides (also called triacylglycerols)
contain:
– Three fatty acid molecules
– One glycerol molecule
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Triglycerides
• Fatty acids are classified by:
– Carbon chain length
– Saturation level
– Shape
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Triglycerides: Chain Length
• Short-, medium-, or long-chain fatty acids
• Carbons can be numbered
– Carboxyl end (COOH): -carbon (alpha—first)
– Methyl end (CH3): Ω-carbon (omega—last)
• Determines method of lipid digestion,
absorption, metabolism, and use
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Triglycerides: Saturation
• Saturated fatty acids have hydrogen atoms
surrounding every carbon in the chain
• Monounsaturated fatty acids lack one hydrogen
atom (one double bond)
• Polyunsaturated fatty acids have more than
one double bond
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Triglycerides: Shape
• Determined by the saturation of the carbon
chains
• Saturated fatty acids pack tightly together and
are solid at room temperature
– Animal fats, butter, and lard are high in
saturated fatty acids
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Triglycerides: Shape
• Unsaturated fatty acids do not stack together
well and are more liquid at room temperature
• Hydrogen atoms at the unsaturated part can be
arranged in different positions:
– Cis: same side of the carbon chain
– Trans: opposite sides of the chain
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Triglycerides
• Hydrogenation: hydrogen atoms are added to
unsaturated fatty acids
– Make oils more solid and more saturated
– Create trans fatty acids
– Reduce oxidation; resist rancidity
– Increase risk of cardiovascular disease
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Triglycerides
• Essential fatty acids: cannot be made by the
body and must be obtained from food
• Linoleic acid (omega-6 fatty acid)
– Found in vegetable and nut oils
• Alpha-linolenic acid (omega-3 fatty acid)
– Found in vegetables, soy, flaxseeds, walnuts
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Triglycerides
• Omega-3 fatty acids found in fish and fish oil
– Eicosapentaenoic acid (EPA)
– Docosahexaenoic acid (DHA)
• Reduce risk of heart disease
– Stimulate prostaglandins and thromboxanes
that reduce inflammatory responses
– Reduce blood clotting and plasma
triglycerides
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Phospholipids
• Phospholipids contain
– Glycerol backbone, two fatty acids, phosphate
• Soluble in water
• Transport fat in the bloodstream
• Manufactured in our bodies (not required)
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© 2014 Pearson Education, Inc.
Sterols
• Sterols contain multiple rings of carbon atoms
• Plant sterols appear to block the absorption of
dietary cholesterol
• Cholesterol is made in our bodies and therefore
is not necessary in the diet
– Sex hormones, vitamin D, bile
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© 2014 Pearson Education, Inc.
Digestion of Fats
• Fat digestion begins in the small intestine
• Cholecystokinin (CCK) and secretin: gallbladder
contractions release bile
• Bile is produced by the liver and stored in the
gallbladder
• Bile emulsifies fat into small droplets
• Pancreatic enzymes break fat into two fatty
acids and a monoglyceride
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Absorption of Fats
• Lipoprotein transports lipids for absorption
• Chylomicron: lipoprotein produced in intestine to
transport lipids from a meal
– Composed of fatty acids surrounded by
phospholipids and proteins
– Soluble in water
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Absorption of Fats
• Chylomicrons are absorbed by cells of the small
intestine, then:
– Travel through the lymphatic system
– Transferred to the bloodstream
• Short- and medium-chain fatty acids are
absorbed more quickly since they are not
arranged into chylomicrons
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Absorption of Fats
• Triglycerides in the chylomicrons must be
disassembled by lipoprotein lipase before they
can enter body cells
• In body cells, triglycerides can be:
– Used immediately for energy
– Used to make lipid-containing compounds
– Stored in muscle and adipose tissues
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
The Roles of Fat
•
•
•
•
•
•
9 kcal per gram
Major fuel at rest
Endurance exercise
Stored energy
Essential fatty acids
Fat-soluble vitamins
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•
•
•
•
Regulates cell function
Maintains membrane
Protects the body
Provides flavors and
textures of foods
• Helps us feel satiated
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How Much Fat?
• Acceptable Macronutrient Distribution Range
(AMDR) for fat: 20−35% of calories
• Minimize saturated and trans fatty acid intake to
lower risk of heart disease
• Active people may need more energy from
carbohydrates and can reduce their fat intake to
20−25% of total calories
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How Much Fat?
• Dietary Reference Intakes (DRIs) set for
essential fatty acids
– Linoleic acid: AMDR of 5−10% of energy
– Alpha-linolenic acid: 0.6−1.2% of energy
– 5:1 to 10:1 ratio of linolenic:alpha-linolenic
acid
• Saturated fat: less than 7% of energy
– Trans fats: reduced to the absolute minimum
© 2014 Pearson Education, Inc.
Food Sources of Fat
• Visible fats
– Fats we add to foods
– Butter, cream, mayonnaise, salad dressings
• Invisible fats
– Fats hidden within foods
– Occur naturally or added during processing
– Baked goods, dairy, meats, fast foods
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Food Sources of Fat
• Beneficial fats
– Omega-3 fatty acids may be low in diets
– Fish, walnuts, soy, canola, flaxseed
• Switching to more healthful fats without
increasing total fat intake
– Use olive or canola oil in place of butter or
margarine
– Select low-fat or nonfat dairy products
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Food Sources of Fat
• Fat replacers
– Used to lower fat content of foods
– Found in chips, cakes, cookies
– May cause GI side effects in large amounts
– Example: olestra (Olean)
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© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Cardiovascular Disease
• Cardiovascular disease
– Dysfunction of the heart or blood vessels
– Can result in heart attack or stroke
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Cardiovascular Disease
• Risk factors for cardiovascular disease:
– Being overweight
– Physical inactivity
– Smoking
– High blood pressure
– Diabetes mellitus
– Inflammation
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© 2014 Pearson Education, Inc.
Cardiovascular Disease
• Dietary fats increase blood lipids
• Highly saturated and trans fat intakes increase
blood cholesterol
• Omega-3 fatty acids reduce inflammation and
blood triglycerides
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Cardiovascular Disease
• Blood lipids include:
– Chylomicrons—present only after a meal
– Very-low-density lipoproteins (VLDL)
– Low-density lipoproteins (LDL)
– High-density lipoproteins (HDL)
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Cardiovascular Disease
• Diets high in saturated fats
– Decrease the removal of LDLs from the blood
– Increase blood cholesterol levels
– Contribute to the formation of plaques that
can block arteries
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Cardiovascular Disease
• Diets high in trans fatty acids:
– Can raise blood levels of LDL-cholesterol as
much as saturated fat
– Are abundant in hydrogenated vegetable oils
(margarine, baked goods, fried foods)
• FDA requires that trans fatty acid content be
listed on labels for conventional foods and some
dietary supplements
© 2014 Pearson Education, Inc.
Cardiovascular Disease
• Lifestyle changes can prevent or reduce
cardiovascular heart disease
– Total fat intake: 20−35% total calories
– Saturated fat: less than 7% total calories
– Cholesterol: less than 300 mg per day
– Trans fat: reduce to absolute minimum
– Increase omega-3 fatty acids
– Dietary fiber: 20−30 grams per day
– Folate: 400 micrograms/day
© 2014 Pearson Education, Inc.
Cardiovascular Disease
• Lifestyle changes can prevent or reduce
cardiovascular heart disease
– Maintain normal blood glucose level
– Eat throughout the day
– No more than 2 alcoholic beverages per day
for men and 1 drink per day for women
– Maintain an active lifestyle
– Maintain a healthful body weight
– Decrease salt intake (DASH diet)
PLAY
© 2014 Pearson Education, Inc.
ABC News Video: On Call: Tips to Raise
Good Cholesterol
Cardiovascular Disease
• Medicines help reduce risk
– Endogenous cholesterol synthesis inhibitors:
statins
– Bile acid sequestrants
– Nicotinic acid
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High-Fat Diets and Cancer
• Three types of cancer have been studied
extensively for their possible relationship to
dietary fat intake:
– Breast cancer
– Colon cancer
– Prostate cancer
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High-Fat Diets and Cancer
• Until the links with cancer are settled, the
American Institute for Cancer Research
recommends these common-sense rules:
– Maintain a healthy body weight
– Engage in moderate physical activity at least
30 min/day
– Limit consumption of sugary foods, empty
Calories, red meats, salty foods, and alcohol
– Eat a variety of fruits, vegetables, and wholegrain foods
© 2014 Pearson Education, Inc.
PLAY
© 2014 Pearson Education, Inc.
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