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5
Lipids: Essential
Energy-Supplying
Nutrients
© 2011 Pearson Education, Inc.
What Are Lipids?
• Lipids
• Diverse group of molecules that are insoluble in
water
• Fats
• The lipid content of diets and foods
© 2011 Pearson Education, Inc.
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 (triacylglycerides) 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
© 2011 Pearson Education, Inc.
© 2011 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
© 2011 Pearson Education, Inc.
© 2011 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
© 2011 Pearson Education, Inc.
© 2011 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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Triglycerides
• Hydrogenation: hydrogen atoms are added to
unsaturated fatty acids
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Make oils more solid and more saturated
Create trans fatty acids
Reduce oxidation; resist rancidity
Increase risk of cardiovascular disease
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
© 2011 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
© 2011 Pearson Education, Inc.
Phospholipids
• Phospholipids contain
• Glycerol backbone, two fatty acids, phosphate
• Soluble in water
• Transport fat in the bloodstream
• Manufactured in our bodies (not required)
© 2011 Pearson Education, Inc.
© 2011 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
© 2011 Pearson Education, Inc.
© 2011 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
Fat Digestion
© 2011 Pearson Education, Inc.
© 2011 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
© 2011 Pearson Education, Inc.
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
Lipid Absorption
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
The Roles of Fat
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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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
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
© 2011 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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Food Sources of Fat
• Fat replacers
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Used to lower fat content of foods
Found in chips, cakes, cookies
May cause GI side effects in large amounts
Example: olestra (Olean)
Fats in Food
© 2011 Pearson Education, Inc.
© 2011 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:
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Being overweight
Physical inactivity
Smoking
High blood pressure
Diabetes mellitus
Inflammation
© 2011 Pearson Education, Inc.
© 2011 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:
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Chylomicrons—present only after a meal
Very-low-density lipoproteins (VLDL)
Low-density lipoproteins (LDL)
High-density lipoproteins (HDL)
Lipoproteins: VLDL, LDL,
and HDL
© 2011 Pearson Education, Inc.
© 2011 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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
© 2011 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
© 2011 Pearson Education, Inc.
Cardiovascular Disease
• Lifestyle changes can prevent or reduce
cardiovascular heart disease
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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
© 2011 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)
Fast Food Trends
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Cardiovascular Disease
• Medicines help reduce risk
• Endogenous cholesterol synthesis inhibitors:
statins
• Bile acid sequestrants
• Nicotinic acid
© 2011 Pearson Education, Inc.