Transcript The Liver - University of Akron

Lipids
Properties of Lipids
Do not readily dissolve in water
Fats are solid at room temperature
Oils are liquid at room temperature
Energy dense (9 kcal /gm)
Three Groups of Lipids
Triglycerides: the main form of lipids in
food and body (storage)
Phospholipids
Sterols
Triglyceride (TG)
Structure
Contain Carbons (C), Hydrogens (H),
Oxygens (O)
Glycerol + 3 fatty acids
Triglycerides
H
O
H--C--OH
HO-C-R
H
H--C--O--C-- R + H2O
O
H--C--OH
+
HO-C-R
O
H--C--O--C-- R + H20
O
H--C--OH
HO-C-R
H
Glycerol
O
O
H--C--O--C-- R + H20
H
+ 3 FA’s
(Ester bond)
Triglyceride +
3 H20
Triglycerides
H
H
H--C--OH
Fatty Acid
H--C--OH
+
Fatty Acid
H--C--O--C-- Fatty Acid
O
H--C--O--C-- Fatty Acid
Fatty Acid
H--C--OH
O
O
H--C--O--C-- Fatty Acid
H
H
esterification
desterfication
Phospholipid
Built on a glycerol backbone
Has at least one fatty acid replaced with
phosphorus compound
Found in body
Synthesized by the body as needed
Phospholipid Structure
Functions of
Phospholipids
Make up cell membrane
Emulsifier
Bile acids
 Lecithins
 Improves food products

Emulsifier
Hydrophilic end
(attracts water)
Hydrophobic end
(attracts lipid)
Emulsification
Cholesterol
Most common sterol
A multi-ringed structure
Does not have a glycerol backbone
Waxy substance
Do not readily dissolve in water
Cholesterol is a sterol
Cholesterol Structure
Dietary Sources of
Cholesterol
Found in animal products only
Never found in plants
However ↑ saturated fat intake ↑ serum
cholesterol
Serum (blood)
Cholesterol
Dietary cholesterol
Endogenous cholesterol
Made in liver
 Increases with increased SFA intake

Functions of Cholesterol
Essential component of cell
membrane
Produced by the liver
Found only in animal products
Forms important hormones

Estrogen, testosterone, vitamin D
Precursor to bile acids
Fatty Acids
Simplest form of lipids
Common to most lipids, in the body and
in foods
Chain of 4-26 carbons bonded together,
flanked by hydrogens
Alpha end: is an acid
Omega end: a methyl group
Fats in foods are generally fatty acid
mixtures
Differences in
Fatty Acids
Number of carbons
Degree of saturation




Number of single or double bonds in carbon chain
Saturated
Monounsaturated
Polyunsaturated
Point of first unsaturated bond


Omega-3
Omega-6
Fatty Acid Structure
H H H H H H H H H H H H H H H HHO
H-C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C-C-OH
H H H H H H H H H H H H H H H H H
omega end
alpha end
stearic acid (C18:0)
Saturated Fatty Acids
(SFA)
All the bonds between carbons are
single connections and the carbons are
filled with hydrogen
Foods containing primarily saturated
fats tend to be solid at room
temperature
Medium chain (coconut oil) and shortchain saturated fatty acids (dairy fat)
may be liquid
Saturated Fatty Acids
Don’t spoil easily, therefore longer shelf
life
High intakes of sfa are associated with
an increased risk of cardiovascular
disease
Sources of SFA
Animal fats (meat, dairy)
Tropical oils (coconut and palm oil)
Hydrogenated fats
Saturated Fatty Acid
Structure
H H H H H H H H H H H H H H H HHO
H-C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C-C-OH
H H H H H H H H H H H H H H H H H
omega end
alpha end
degree of saturation: single carbon bond
stearic acid: C18:0
Monunsaturated
Fatty Acids (MFA)
One double bond between the
carbons (missing hydrogens)
Liquid at room temperature
Easily oxidized → becomes rancid
 Double
bonds are weak points
 Easily broken by oxygen (oxidized)
Monounsaturated
Fatty Acids
Canola, olive, peanut oil contain a high
percentage of monounsaturated fatty
acids
MFA decreases CVD risk
Monounsaturated
Fatty Acid Structure
H H H H H H H H
H H H H H H H O
H-C--C--C--C--C--C--C--C--C=C--C--C--C--C--C--C--C--C-OH
H H H H H H H H H H H H H H H H H
omega end
One double bond
ω-9 C18:1
alpha end
Polyunsaturated
Fatty Acids (PUFA)
More than one double bond
between the carbons
Liquid at room temperature
Easily oxidized
Polyunsaturated fat decreases
CVD risk when substituted for SFA
Polyunsaturated
Fatty Acids
Corn, soybean, sunflower, and
safflower oils are rich in
polyunsaturated fatty acids (PUFA)
Polyunsaturated Fatty
Acid Structure (Fig. 5-1-C)
H H H H H
H
H H H H H HH O
H-C--C--C--C--C--C=C--C--C=C--C--C--C--C--C--C--C--C-OH
H H H H H H H H H H H H H H H H H
omega end
> 2 double bonds
alpha end
Fatty Acid Profiles in Foods
Hydrogenation of Fatty
Acids
Addition of H to C=C double bonds
Breaks double bonds
Formation of trans fatty acid
(similar to shape of saturated
fatty acid)
Hydrogenation of
Fatty Acids
Process used to solidify an oil
Resistant to oxidation
 Increases
shelf life
 Can be reused longer in frying
However resulting trans fatty acids
are associated with ↑ CVD risk
Cis and Trans Fatty Acid
Health Dangers of
Trans Fatty Acids
Raises LDL
Lowers HDL
Increases risk for heart disease
Current intake is~3% of total kcals
Soon to be on food labels
Sources of
Trans Fatty Acid
Stick margarine
Shortening
Crackers
Hydrogenated fats
Deep-fried foods
High fat baked goods
Non-dairy creamers
Rancidity
Decomposed oils
Breakdown of the C=C double
bonds by ultraviolet rays, &/or O2
Yields unpleasant odor and flavor
PUFA more susceptible
Limits shelf life
Prevention of Rancidity
Hydrogenation
Addition of vitamin E
Addition of Butylated
hydroxyanisol (BHA) and
Butylated hydroxytolune (BHT)
Functions of Fats
Provide essential fatty acids
Provide energy (muscles and many
organs burn fat)
Supply fat soluble vitamins
Satiety
Texture and flavor
Essential Fatty Acids
Body can only make double bonds
after the 9th carbon from the
omega end
Needed for immune function,
vision, cell membrane, and
production of hormone-like
compounds
Essential Fatty Acid- Omega-3
(alpha-linolenic acid)
H H H H H H H H H H H H H H H HH O
H-C--C--C=C--C--C =C--C--C=C--C--C--C--C--C--C--C--C-OH
H H
H
H
H H H H H H H
omega end
alpha end
1st double bond is located on the 3rd carbon
from the omega end
Omega-3 Fatty Acid
Primarily from fish oil
Also found in canola or soybean oil
Recommend intake of ~2 servings of
fish per week
Essential Fatty Acid- Omega-6
(alpha-linoleic acid)
H H H H H
H
H H H H H H H O
H-C--C--C--C-- C--C =C--C--C=C--C--C--C--C--C--C--C--C-OH
H H H H H H H H H H H H H H H H H
omega end
alpha end
1st double bond is located on the 6th carbon
from the omega end
Omega-6 Fatty Acid
Found in vegetable oils
Only need
~ 1 tablespoon a day
Essential Fatty Acids
Omega-3
Omega 6
Alpha-linolenic acid
DHA
(docosahexanoic
acid)
EPA
(eicosapentaenoic
acid)
Linolenic acid
Arachidonic Acid
Effects of Essential
Fatty Acids
Archidonic acid (Omega-6 )


increase blood clotting
increase inflammatory responses
DHA, EPA (Omega-3)




decrease blood clotting
reduces heart attack
excess may cause hemorrhagic stroke
large amounts may decrease inflammation pain
with rheumatoid arthritis
Signs and Symptoms of
Essential Fatty Acids
Deficiency
Flaky, itchy skin
Diarrhea
Infections
Retarded growth and wound healing
Anemia
Functions of Body Fat
Energy store
Adipose cells
 1 pound fat = 3500 calories

Insulation

Subcutaneous fat
Protection

Internal organs
Lipids in Foods
Hidden Fat
Look on the Nutrition Facts
Look on the lists of ingredients
Control portion size
Reduced Fat Foods
Sugar is commonly
added in place of
fat
Check calorie
content
Fat Substitutes
Water (diet margarine)
Z-trim (starch derivative that binds with
water)
Fiber cellulose (Maltrin, Stellar, Oatrim)
Dairy-Lo (protein globules)
Olestra (links fatty acid to sucrose)
not digested
 fat-soluble vitamins issue

Digestion of Fat in the
Stomach
Gastric lipase works only in an acidic
environment
Gastric lipase acts on triglycerides
containing short & medium chain fatty
acid
Longer fatty acid chain is not affected
by the stomach
Digestion of Fat in the
Small Intestine
Primary site of fat digestion
CCK stimulates pancreas to release pancreatic
lipase
Pancreas release lipase
Bile acid emulsifies digested fat
Fat is broken down to monoglycerides and
fatty acids
Absorption of Fat
Diffuse into the absorptive cells
Short and medium chain (<12 C) fatty
acids are water soluble

Enters the portal system
Long chain fatty acids reforms into TG

Enters the lymphatic system
Carrying Fat in the
Bloodstream
Water (blood) and oil (fat) are
incompatible
Unique system of fat transportation is
needed
Fat
Transportation of
Digested Fat
Re-formed into triglycerides
Packaged into chylomicrons
Lipoprotein lipase breaks down
triglycerides in the chylomicrons
Fatty acids are absorbed by cells
Takes 2-10 hours to clear chylomicron
Lipoproteins
Transportation of
Synthesized Fat
Fat and cholesterol made primarily by the
liver
Very Low Density Lipoprotein (VLDL)
Low Density Lipoprotein (LDL)
Receptor pathway for cholesterol uptake
Scavenger pathway for cholesterol uptake
Scavenger Pathway
Scavenger WBC removes (oxidized) LDL
from circulation
Prevents oxidized LDL from returning to
circulation
Build-up of plaque on walls of the blood
vessels
Leads to plaque and atherosclerosis
Causes: smoking, diabetes, HTN,
homocysteine, LDL
Antioxidant
Reduces oxidation
Slows LDL uptake into scavenger
cells
Need for supplements of
antioxidants?
High Density Lipoprotein
(HDL)
Synthesized by liver and intestine
High proportion of protein
Picks up cholesterol from dying cells and
other sources
Transfers cholesterol to other lipoproteins for
transport to the liver for excretion
HDL can also transfer directly back to the
liver
Benefits of (a high) HDL
(level)
Remove cholesterol from the blood
stream
HDL may block oxidation of LDL
Reduce risk of heart disease
Pre-menopausal women have higher
HDL
Functions of Lipids
Provide energy
Efficient storage of energy
Insulation
Protection
Transport fat-soluble vitamins
Satiety
Flavor and mouth feel
Recommendation
No RDA
4% of total kcal should come from
essential fatty acids
No more than 15% from PUFA
Current diet supplies ~33% of total kcal
from fat

much from animal, whole milk, pastries,
cheese, margarine, and mayo
Dietary Reference
Intakes (2002 Update)
20-35% total calories from fat
≤30% with typical American diet
Up to 35% with more monunsaturated
fat
American Heart Association
Population Guidelines
≤10% total calories from lipid-raising
fats (saturated fat and trans fat)
≤10% total calories from
polyunsaturated fat
At least 10% of calories from
monounsaturated fat
<300 mg cholesterol/day
Eat two servings of fish/week