Download Lipids NTR150

Lipids
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
What Are Fats?
Fats are one type of lipid.
Lipids: diverse class of molecules that are
insoluble in water.
Lipids (fats) do not dissolve in water.
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What Are Fats?
Three types of lipids are found in foods:
(1) Triglycerides
(2) Phospholipids
(3) Sterols
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Triglycerides
Triglycerides are composed of
• Three fatty acid molecules
• Fatty acids are long chains of carbon atoms
surrounded by hydrogen atoms
• One glycerol molecule
• Glycerol is a 3-carbon alcohol that is the
backbone of a triglyceride
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Triglycerides
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Triglycerides
Fatty acids can differ in
• Length of their carbon chain
• Short-, medium-, or long-chain
• Level of saturation
• Saturation refers to how many hydrogen atoms
surround each carbon
• Shape
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Names of some common Fatty Acids
Lipid
# Carbons
Lauric Acid
Myristic Acid
Palmitic Acid
Stearic Acid
Oleic Acid
Linoleic Acid
Conjugated Linoleic Acid
Alpha-Linoleic Acid
Gamma-Linoleic Acid
Di-homo-Gamma-Linoleic Acid
Arachidonic Acid
12
14
16
18
18
18
18
18
18
20
22
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# double bonds
0
0
0
0
1
2
2
3
3
3
4
# omega
none
none
none
none
omega-9
omega-6
omega-6
omega-3
omega-6
omega-6
omega-6
Triglycerides
Saturated fatty acids have a hydrocarbon tail that
consists of single-bonded carbons only.
Monounsaturated fatty acids contain one double
bond in the hydrocarbon tail.
Polyunsaturated fatty acids contain multiple
double in the hydrocarbon tail.
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Triglycerides
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Triglycerides
The shape of a triglyceride is determined by the
saturation of the carbon chains.
Saturated fatty acids can pack tightly together
and are solid at room temperature.
• For example animal fats, butter, and lard are
high in saturated fatty acids.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Triglycerides
Unsaturated fatty acids do not stack together well
and are liquid at room temperature.
• Plant oils have unsaturated fatty acids.
The hydrogen atoms at the unsaturated region
can be arranged in different positions:
• Cis – same side of the carbon chain
• Trans – opposite sides of the chain
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Triglycerides
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Triglycerides
Hydrogenation: The addition of hydrogen atoms
to unsaturated fatty acids.
• Coverts liquid fats (oils) into a more solid
form
• Used to create margarine from plant oil
• Often creates trans fatty acids
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Phospholipids
Phospholipids
• Are composed of
• Glycerol backbone
• 2 fatty acids
• Phosphate
• Are soluble in water
• Are manufactured in our bodies so they are not
required in our diet
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Phospholipids
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Sterols
Sterols: Lipids containing multiple rings of
carbon atoms.
• Are essential components of cell membranes
•
and many hormones
Are manufactured in our bodies and therefore
are not essential components of our diet
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Sterols
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Digestion of Fats
Fats are not digested and absorbed easily because
they are insoluble in water.
Very little digestion of fats occurs in the watery
environments of the stomach and mouth.
Most digestion of fats begins in the small
intestine.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Digestion of Fats
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Digestion of Fats
As fat enters the small intestine
• Bile is secreted from the gall bladder into the
•
•
•
small intestine
Bile is produced by the liver and stored in the
gall bladder
Bile disperses fat into smaller fat droplets
Pancreatic enzymes break fat into 2 separate
fatty acids and a monoglyceride
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Digestion of Fats
Fatty acids are arranged as lipoproteins for
absorption and transport.
Chylomicron: A lipoprotein produced by cells
lining the small intestine.
• Composed of fatty acids surrounded by
•
phospholipids and proteins
Soluble in water
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Structure of a Lipoprotein
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Digestion 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.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Digestion of Fats
Triglycerides in the chylomicrons must be
disassembled by lipoprotein lipase before they
can enter body cells.
After entering body cells, triglycerides can be
• Used immediately for energy
• Used to make lipid-containing compounds
• Stored in liver and muscle cells
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The Role of Fat
Energy
• Fat is very energy dense, containing 9 kcal per
•
•
•
gram.
Much of the energy used during rest comes
from fat.
Fat is used for energy during exercise,
especially after glycogen is depleted.
Fat is also used for energy storage.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
The Role of Fat
Essential fatty acids
• Two fatty acids cannot be synthesized in the
body and must be obtained in the diet:
(1) Alpha-linoleic acid (omega-3 fatty acid)
• Found in vegetables, fish and fish oils
(2) Linoleic acid (omega-6 fatty acid)
• Found in vegetable and nut oils
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What foods are rich in Omega-3?
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Essential Fatty Acids
“Essential for well-being”:
•Lowers the risk of breast and colon cancer
•Improve learning and attention span in schoolchildren
•Improve cognitive function in the elderly
•Elevate mood, resulting in less depression
•Lower the risk of cardiovascular disease
•Promote healthy skin
•Improve vision, especially night vision
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The Role of Fat
Fat-soluble vitamins
• Vitamins A, D, E, and K are soluble in fat; fat is
required for their transport
Fat is essential to many body functions
• Cell membrane structure
• Nerve cell transmissions
• Protection of internal organs
• Insulation to retain body heat
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
The Role of Fats
Fat provides flavor and texture to foods.
Fat contributes to making us feel satiated because
• Fats are more energy dense than carbohydrates
•
or protein
Fats take longer to digest
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How Much Fat?
The Acceptable Macronutrient Distribution
Range (AMDR) for fat:
20-35% of calories should be from fat
Athletes and highly 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?
The type of fat consumed is important.
• Saturated fat should be no more than 7% of
•
•
total calories.
Trans fatty acids should be reduced to the
absolute minimum.
Most fat in our diets should be from
monounsaturated fats (eg., olive oil).
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Food Sources of Fat
Visible fats
• Fats we knowingly add to foods
• Butter, cream, mayonnaise, dressings
Invisible fats
• Fats hidden in foods
• Naturally occurring or added during processing
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Health Problems From Fat
Cardiovascular disease
• Dysfunction of the heart or blood vessels
• Can result in heart attack or stroke
The type of fat in our diet can contribute to or
protect against cardiovascular disease.
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Cardiovascular Disease
Risk factors for cardiovascular disease include
• Being overweight
• Physical inactivity
• Smoking
• High blood pressure
• Diabetes
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Cardiovascular Disease
Blood lipids include
• Chylomicrons
• VLDLs – very low-density lipoproteins
• LDLs – low-density lipoproteins
• “bad cholesterol”
• HDLs – high-density lipoproteins
• “good cholesterol”
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Types of Blood Lipids
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Cardiovascular Disease
Diets high in saturated fats
• Decrease the removal of LDLs from the blood
• Contribute to the formation of plaques that can
•
block arteries
Increase triglyceride levels (chylomicrons and
VLDLs)
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Cardiovascular Disease
Cross-section of (a) a normal artery and (b) a partially blocked artery.
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Cardiovascular Disease
Trans fatty acids:
• Can raise blood cholesterol levels as much as
•
•
saturated fat
Are abundant in hydrogenated vegetable oils
(margarine, vegetable oil spreads)
Should be reduced to the absolute minimum
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Cardiovascular Disease
How can fat intake protect against heart disease?
Diets high in omega-3 fatty acids (along with
moderate exercise) can increase HDL “good”
cholesterol levels.
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What are “fat-replacers”?
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What are “fat replacers”?
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
What are “fat replacers”?
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings