Download NSCC NTR150 Ch05 Fats (Lipids)

Chapter 5 - Fats
taught by
Norman D. Sossong, MD, PhD
NSCC – NTR150 – Spring 2008
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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Lipids
Description:
• A nonpolar, organic molecule
• Fatlike
• Insoluble in water
• Dissolve readily in nonpolar organic solvents
Lipid Types
Fats
Oils
Waxes
Steroids
Phospholipids
Carotenoids
What Are Fats?
Three types of lipids are found in foods:
• Triglycerides
• Phospholipids
• Sterols
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Lipids: Fats = Triglycerides
Composed of:
• Glycerol
• Fatty acids
Ratio of H:O > 2:1
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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Glycerol
A 3-carbon alcohol
One hydroxyl group on each carbon
Glycerol + 3 Fatty Acids →
Triglyceride
Fatty acids
Long hydrocarbon chains ending in a carboxyl
(-COOH) group
• Typical length is 14 to 20 carbon atoms
Fatty Acids in Triglycerides
Fatty acids can differ in
• Length of their carbon chain
• Level of saturation
• Shape
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Fatty Acids Differ in Length
Short-, medium-, or long-chain
Chain Length
• 4-24 carbons
• Typical length;
• 14-24 carbon
atoms
Fatty Acids in Triglycerides
Fatty acids can differ in
• Length of their carbon chain
• Level of saturation
• Saturation refers to how many hydrogen atoms
surround each carbon
• Shape
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3 Types of Fatty
acids
Saturated
Unsaturated
Polyunsaturated
Fatty acids
Saturated
• All the internal carbon atoms have single bonds with
either C or H
• This represents the maximum amount of H atoms that
can be attached
• (Animal fats are typically saturated)
Saturated Fat
Fatty acids: Levels of Saturation
Saturated
Unsaturated
• One, or more, of the carbons are attached with 2 or 3
bonds
• Bend at the double bonds
• (Most plant fats are unsaturated;
•
Palm & coconut oils are notable exceptions)
Unsaturated Fat
Polyunsaturated Fat
Polyunsaturated
• There are 2 or more double
bonds
• Bend at the double bonds →
• Low melting points
• Usually liquid at room
temperatures = oil
Fatty Acids: Level of Saturation
Degree of saturation
•
Saturated
• All single bonds between carbons
• Monounsaturated
• One carbon-carbon double bond
•
Polyunsaturated
• More than one carbon-carbon double bond
Lipids: Fats = Triglycerides
Physical Properties
• Saturated Fats
• Tend to be solids at room temperature
• Unsaturated Fats
• Tend to be liquids at room temperature
Applications & Sources
• Saturated Fats
• Tend to be structurally useful in land animals
• Unsaturated Fats
• Tend to be found in
cold-water fish & plants
Triglycerides
Fatty acids can differ in
• Length of their carbon chain
• Level of saturation
• Shape
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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.
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Triglycerides
Saturated fatty acids have hydrogen atoms
surrounding every carbon in the chain.
Monounsaturated fatty acids lack hydrogen
atoms in only one region.
Polyunsaturated fatty acids lack hydrogen atoms
in multiple locations.
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Triglycerides
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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
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Fatty acids
Saturated
Unsaturated
Polyunsaturated
Cis- vs. trans- fatty acids
Triglycerides
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Fatty Acids Are Key Building Blocks
Types of fatty acids
• Cis and trans
• Hydrogenation produces trans fatty acids
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
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Fatty Acids Are Key Building Blocks
Types of fatty acids
• Cis and trans
• Hydrogenation produces trans fatty acids
• Essential fatty acids
• Linoleic acid and alpha-linolenic acid
• Can’t be made in the body
• Used to make eicosanoids
Triglycerides = Fats
Structure
• Glycerol + 3 fatty acids
Functions
• Energy source and reserve
• Insulation and protection
• Carrier of fat-soluble vitamins
• Sensory qualities in food
Lipids: Fats = Triglycerides
Used to store energy in organism
• 9 kilocalories (kcal)/gram
• [compared with 4 kcal/gram for carbohydrates]
• Saturated fats tend to have more energy than
unsaturated fats
• 2 C-H vs. 1 C=C
• → animal fats usually have more calories than do
vegetable fats
Triglycerides in Food
Sources of omega-3 fatty acids
• Soybean, canola, walnut, flaxseed oils
• Salmon, tuna, mackerel
Sources of omega-6 fatty acids
• Vegetable oils
• Nuts and seeds
Photos © PhotoDisc
What Are Fats?
Three types of lipids are found in foods:
• Triglycerides
• Phospholipids
• Sterols
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Phospholipids
•
Are composed of
• Glycerol backbone
• 2 fatty acids
• Phosphate
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Phospholipids
•
Are composed of
• Glycerol backbone
• 2 fatty acids
• Phosphate
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Phospholipids
Modified fats
• = a triglyceride with one fatty acid chain replaced by
a phosphate-containing group
Phospholipids
Composed of
• Polar “head” (phosphate group) at one end
• 2 nonpolar “tails” at the other end
Phospholipids
Composed of
• Polar “head”
•
(phosphate group) at
one end
2 nonpolar “tails” at the
other end
Phospholipids
• Form bilipid layers which form biological
membranes
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Phospholipids
• Are soluble in water
• Are manufactured in our bodies;
so they are not required in our diet
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Phospholipids: Summary
Structure
• Glycerol + 2 fatty acids +
phosphate group
Functions
• Component of cell membranes
• Lipid transport as part of
•
lipoproteins
Emulsifiers
Food sources
• Egg yolks, liver, soybeans, peanuts
What Are Fats?
Three types of lipids are found in foods:
• Triglycerides
• Phospholipids
• Sterols
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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
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Sterols
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Cholesterol
Cholesterol
Sterols: Cholesterol
Functions
•
•
Component of cell membranes
Precursor to other substances
• Sterol hormones
• Vitamin D
• Bile acids
Synthesis
•
•
Made in the liver
From saturated fats
Food sources
•
Found only in animal foods
Steroids
Composed of 4 carbon rings
Examples
• Cholesterol
• Estrogen
• Progesterone
• Aldosterone
• Testosterone
Lipid and Lipid-Related Molecules
Digestion of Fats
Fats are not digested and absorbed easily because
they are insoluble in water.
No digestion of fats occurs in the watery
environments of the mouth or stomach.
Digestion of fats begins in the small intestine.
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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
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Digestion of Fats
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Digestion and Absorption
Mouth and stomach
• Minimal digestion of triglycerides
Small intestine
• Emulsified by phospholipids
• Digested by pancreatic lipase
• Absorbed into intestinal cells
• Formed into chylomicrons and moved into
lymphatic system
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.
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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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Cholesterol Transport
in Blood
Lipoproteins
• Chylomicrons
• VLDL = Very Low
•
•
Density Lipoproteins
LDL = Low Density
Lipoproteins
HDL = High Density
Lipoproteins
Lipids in the Body
Lipoproteins carry lipids around the body
• Chylomicrons
• Delivers dietary lipids from
intestines to cells and liver
Lipids in the Body
Very-low-density lipoproteins (VLDL)
•
Deliver triglycerides to cells
Low-density lipoproteins (LDL)
• Deliver cholesterol to cells
High-density lipoproteins (HDL)
•
Pick up cholesterol for removal or recycling
Lipoprotein
Composition
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.
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The Role of Fat
Essential fatty acids
• Two fatty acids cannot be synthesized in the
body and must be obtained in the diet
• Alpha-linoleic acid (omega-3 fatty acid)
• Found in vegetables, fish and fish oils
• Linoleic acid (omega-6 fatty acid)
• Found in vegetable and nut oils
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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
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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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Lipids in the Diet
Recommended intake
•
•
•
•
Reduce saturated and trans fat intake
• Saturated fats → ↑ cholesterol production
• Trans fat → ↑ risk of heart attacks
Total fat: 20-35% of calories
Need ~ 2% of calories as essential fatty
acids
Improve balance of
omega-3: omega-6 fatty
acids
Photos © PhotoDisc
What are sources of highly saturated fats?
Animal products such as:
• Lard
• Pork
• Beef
• Lamb
• Chicken fat
•
Butterfat
• Cream
• Butter
• Cheese
(Note: fish oil is not
very saturated)
What are sources of highly saturated fats?
Vegetable products such as:
• Coconut oil
• Palm oil
• Chocolate
Note: both coconut oil and palm oil are widely used in prepared
foods such as:
• Cakes
• Puddings
• Frozen dinners
Unsaturated Fats
Are oils at Room Temperatures
Help reduce cholesterol in the blood
Types:
• Monounsaturated
• Polyunsaturated
Monounsaturated Fat Sources
Olive oil
Canola oil
Peanut oil
Almonds
Avacados
Cashews
Polyunsaturated Fat Sources
Corn oil
Soybean oil
Safflower oil
Sunflower oil
Cottonseed oil
Sesame oil
Walnuts
Cholesterol Sources
Not made by plants
Animal kingdom
• Humans
• Liver
• Saturated fats  the amount made
• Foods of animal origin
Foods of Animal Origin That Act as
Cholesterol Sources
Shell fish
Meats
Poultry
Egg yolks (but not egg whites)
Cream (and products made from cream)
• Butter
• Cheese
• Ice cream
Lipids and Health
Obesity
• High fat diets promote weight gain
Heart disease
• High saturated and trans fat intake raises LDL
cholesterol
Cancer
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
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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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Lipids in the Diet
Fat substitutes
• Different types of
•
composition
Olestra
• Sucrose + fatty acids
• Indigestible – provides
zero kcals
• Reduces absorption of
fat-soluble vitamins