Fats
What Are Fats?
• A type of lipid
• Lipids: A macromolecule; insoluble in water
• Three types of lipids found in foods:
– Triglycerides ** (Dietary Fat)
– Phospholipids
– Sterols
Triglycerides
Triglycerides
• Fatty acids differ in
– Length of carbon chain
• Short-, medium-, or long-chain
– Degree of saturation
• Saturation refers to how many H atoms surround
each carbon
– Shape
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 regions
Triglycerides
Triglycerides
• Shape is determined by saturation of the
carbon chains
• Saturated fatty acids pack tightly
together; solid at room temperature (RT)
– Ex: animal fats, butter, and lard are high in
saturated fatty acids
Triglycerides
• Unsaturated fatty acids do not stack;
they are liquid at RT
– Ex: Plant oils are high in unsaturated fatty
acids
• H atoms at the unsaturated region can be
arranged in different positions:
– Cis – same side of the carbon chain
– Trans – opposite sides of the chain
Triglycerides
Triglycerides
• Hydrogenation: Addition of H atoms to
unsaturated fatty acids
– Converts liquid fats (oils) into a more solid
form (increases shelf life by preventing rotting,
improves baking properties)
– Margarine is just hydrogenated plant oil
– Often creates trans fatty acids
• Tend to decrease useful lipoproteins and
increase harmful lipoproteins
Phospholipids
Sterols
• Lipids containing multiple Carbon rings
– Components of cell membranes & hormones
– Manufactured in our bodies; not essential
components of our diet
Digestion of Fats
• Not easily digested & absorbed because they are
insoluble in water
• No chemical digestion occurs in watery
environments of digestive tract.
– Where is that?
– Only mechanical digestion occurs: mixing, exposing
• Most digestion of fats occurs in the SI
Digestion of Fats
Fats in SI
• As fat enters the small intestine
– Bile is released from gall bladder & liver into SI.
• Made from cholesterol, produced by liver, stored in gall
bladder
Fats in SI
• Bile disperses fat into smaller fat droplets
– Hydrophobic portions surround fats; hydrophilic
portions face watery environment.
Fats in SI
– Pancreatic lipase break fat into 2 fatty acids
and one monoglyceride
Absorption & Transport
• Long 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
Structure of Lipoproteins
Chylomicrons
• Chylomicrons are produced by SI, then:
– Travel through lymphatic system
– Transferred to the bloodstream near heart,
finally to liver
• Short- and medium-chain fatty acids
absorbed more quickly since they are not
arranged into chylomicrons
Absorption of Fat
Small intestine
Stomach
Monoglyceride
Short-chain
fatty acids
Medium-chain
fatty acids
Glycerol
Chylomicrons
Micelle
Protein
Triglyceride
Lacteal
(lymph)
Capillary network
Chylomicron
Blood vessels
To blood
To liver
Longchain
fatty
acids
Size and Compositions of the Lipoproteins
Protein
Phospholipid
Cholesterol
Triglyceride
100
Chylomicron
80
VLDL
Percent
LDL
Protein
60
40
Cholesterol
20
Phospholipid
HDL
Triglyceride
0
Chylomicron
VLDL
LDL
HDL
Chylomicrons
•
Triglycerides inside chylomicrons are
disassembled by lipoprotein lipase before
they enter liver, muscle or adipose cells
•
Uses of Triglycerides
1. Immediately for energy
2. To make lipid-containing compounds
3. Stored in liver and muscle cells
• Lipoproteins: Wiley
Roles of Fats
1.
2.
3.
4.
5.
6.
Energy
Essential Fatty Acids
Fat Soluble Vitamins
Essential to body functions
Flavor and texture
High satiety value (makes us feel full)
The Role of Fat
• Energy
– Fat is energy dense, containing 9 kcal/g
– Primary source during rest, low-intensity
exercise, and after glycogen is depleted
– Excellent energy storage
Essential fatty acids
• 2 fatty acids cannot be synthesized; 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
Vitamins & other functions
• 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
Flavor, texture, satiety
• Provide flavor and texture
• Contributes to making us feel full because:
– Fats are more energy dense than carbs or
protein
– Fats take longer to digest
How Much Fat?
• Acceptable Macronutrient Distribution
Range (AMDR) for fat:
– 20-35% of calories should be from fat
• 65 g fat based on 30% of 2000-kcal diet
• Athletes and highly active people need
more energy from carbohydrates. Can
reduce fat intake to 20-25% of total
How Much Fat?
• Type of fat consumed is important
– Saturated fat - no more than 7-10% of total
calories
• 20 g saturated fat based on 10% of 2000-kcal diet
• 300 mg cholesterol
– Trans fatty acids – None, if you can do it
– Most dietary fat should come from
monounsaturated fats (eg., olive oil)
Health Problems From
Excess Fat
• Cardiovascular disease:
– Any dysfunction of the heart or blood vessels
• Blockage, swelling, weakening
– May result in heart attack or stroke
• Type of fat in our diet can either
contribute to or protect against
cardiovascular disease
Causes of Death
Leading Causes of Death
Leading Causes of Death
Cardiovascular Disease
• Heart disease + cerebrovascular disease
• Risk factors include
–
–
–
–
–
Being overweight
Physical inactivity
Smoking
High blood pressure
Diabetes
Types of Blood Lipids
• Blood lipids:
– Chylomicrons - transport dietary
lipids to liver & some body
tissues
– VLDLs – very low-density
lipoproteins; transport lipids
from liver to peipheral cells
– LDLs – low-density lipoproteins.
Also transport triglycerides
peripheral cells
• “bad cholesterol”
– HDLs – high-density lipoproteins
• “good cholesterol”
Cholesterol is cholesterol
• Where/how it is used
determines whether it
is “bad” or “good”
– LDL = many cholesterols,
which adhere to arterial
walls
– HDL = Mostly protein;
grabs cholesterol from
tissue cells and returns it
to liver
Cardiovascular Disease
•
Diets high in saturated fats
1. Decrease removal of LDLs from the blood
•
Contribute to the formation of plaques that can
block arteries
2. Increase triglyceride levels (chylomicrons and
VLDLs)
•
•
More VLDLs means more LDLs
Exercise can encourage rapid uptake (by cells) of
LDLs and their removal from bloodstream
Cardiovascular Disease
Cross-section of (a) a normal artery and (b) a partially blocked artery
Cardiovascular Disease
• Trans fatty acids:
– Can raise blood cholesterol levels as much as
saturated fat
– Abundant in hydrogenated (processed)
vegetable oils (margarine, vegetable oil
spreads)
Cardiovascular Disease
• Fat intake can protect against heart
disease?
• Diets high in omega-3 fatty acids (along
with moderate exercise) can increase HDL
“good” cholesterol levels
– Removes stray cholesterol from tissue cells &
arteries
Fat content of meats
Fat Content of Meats
Fat Content (mg/100g)
35
30
25
20
15
10
5
0
Feedlot (Beef)
Feedlot
(bison)
Range (bison) Range (Beef)
Type of Meat
Elk
Chicken
Days on grain affects fat
concentration
Decline in Omega 3 Fatty Acids
Percent TOTAL lipid conc
1.20
1.00
0.80
ALA
0.60
EPA
DHA
0.40
0.20
0.00
0
28
56
84
112
Days on grain
140
168
196