Transcript Slide 1

The Lipids:
Triglycerides,
Phospholipids, and
Sterols
Chapter 5
Fig. 5-CO, p. 132
Introduction
 Poor health
 Too much fat
 Too little fat (unlikely in U.S.)
 Too much of some kinds of fat
 Family of lipids
 Triglycerides- fats and oils
 Phospholipids
 Sterols
Overview of Fatty Acids and
Triglycerides
 Energy provided per gram
 More carbons and hydrogens per oxygen
 Preview of lipids from diet
 Triglycerides: 1 glycerol plus 3 fatty acids
 Fatty acids have even number of carbons
 Fatty acids are saturated or unsaturated
 Omega-3 and omega-6 fatty acids
Chemist’s View of Fatty Acids
and Triglycerides
 Fatty acids
 Organic (carbon-based) acid
 Methyl group at one end; acid group at other
end
 Usually even number of carbons, 4-24
 18-carbon fatty acids abundant in food
 Saturations
 Saturated – full of hydrogens, no double bonds
 Unsaturated – missing hydrogens
Acid
end
Methyl
end
Up to 22 more carbons
p. 138
Saturated Fatty Acids
 NO double bonds
 Solid at 77 F
 Found in meat, dairy, tropical fat
 Max. allowed is 1/3 total daily fat
Stearic Acid
Fully saturated,
no double bonds
Stearic Acid
Zero double bonds
Polyunsaturated
Fatty Acids (PUFA’s)
 Omega-3: 1st double bond is 3 carbons
from methyl end; ex: linolenic acid
• fatty fishes
 Omega-6: 1st double bond is 6 carbons
from methyl end; ex: linoleic acid
 many vegetable oils
 Liquid at 77 F
PUFA’s
Linolenic acid, an omega-3 fatty acid
Omega carbon
at #3
Acid end
Methyl end
Linoleic acid, an omega-6 fatty acid
Omega carbon
at #6
Acid end
Methyl end
Monounsaturated
Fatty Acids (MUFA’s)
 One double bond
 Most MUFA in diet are omega-9
 Oleic acid most common MUFA
 Olive, safflower, canola oils
 Liquid at 77 F
Impossible configuration
One Double Bond
Mono= one point of unsaturation
Linoleic acid, an 18-carbon PUFA
2 double bonds
Linoleic acid
Double bond
Saturated fatty acids tend to stack
together. Consequently, saturated
fats tend to be solid (or more firm)
at room temperature.
This mixture of saturated and
unsaturated fatty acids does not
stack neatly because unsaturated
fatty acids bend at the double
bond(s). Consequently,
unsaturated fats tend to be liquid
(or less firm) at room temperature.
Fatty Acids
 Distinction by location of double bonds
 Omega number is 1st double bond
nearest the methyl end of the carbon
chain
 Linolenic acid 3 dbl bonds, minus 6 H+
 Linoleic acid 2 dbl bonds, minus 4 H+
 Monounsaturated fatty acids
 Omega-9 groups
PUFA’s in Food
Linolenic acid, an omega-3 fatty acid
Omega carbon
at #3
Acid end
Methyl end
Linoleic acid, an omega-6 fatty acid
Omega carbon
at #6
Acid end
Methyl end
Triglycerides (TG)
 Glycerol backbone
 Three fatty acids
 Formed via series of condensation
reactions
 Usually contain mixture of fatty
acids
Glycerol
How Triglycerides are Made
Glycerol + three fatty acids
An H atom from glycerol and an OH group
from a fatty acid combine to create water,
leaving the O on the glycerol and the C at the
acid end of each fatty acid to form a bond.
Saturation vs Unsaturation
 Firmness
 Poly and Monounsaturated fats
 Saturated fats
 Length of carbon chain- shorter
 Stability
 Oxidation and spoilage of fats
 Saturated fats are more stable
 Antioxidants BHA, BHT, Vitamin E
softer
Hydrogenation
 Adding H2 to PUFA’s to reduce
double bonds, making them more
saturated / solid and more resistant
to oxidation which leads to rancidity.
 Hydrogenation produces trans fatty
acids
How to Make Trans from Poly
with Hydrogen Gas
Hydrogenation
 Advantages
– Shelf life
– Texture improvement
 Disadvantages
 Acts like saturated fat in the blood,
only worse
Cis- and Trans-
cis-fatty acid
trans-fatty acid
A cis-fatty acid has its hydrogens
on the same side of the double
bond; cis molecules fold back into
a U-like formation. Most naturally
occuring unsaturated fatty acids in
foods are cis.
A trans-fatty acid has its hydrogens on
the opposite sides of the double bond;
trans molecules are more linear. The
trans form typically occurs in partially
hydrogenated foods when hydrogen
atoms shift around some double bonds
and change the configuration from cis to
trans.
Phospholipid (PL)
• Compound similar to a
triglycerides but has a phosphate
group and choline in place of one
of the fatty acids
• Lecithin most common one
Phospholipid
From 2
fatty acids
The plus charge on the N is
balanced by a negative ion—
usually chloride.
From choline
From glycerol
From phosphate
Phospholipids
 Phospholipids
 Solubility in fat and water
 Emulsifiers in food industry (lecithin)
 Food sources- egg yolk, liver, soy, peanuts
 Roles in the Body
 Part of cell membranes
 Emulsifiers
Cell Membrane
Outside cell (ECF)
Glycerol heads
Fatty acid tails
Glycerol heads
Inside cell (ICF)
Sterols
 Cholesterol
 Food sources and production of 800-1500
mg/d by liver
 Plant sterols inhibit cholesterol absorption
 Body compounds made from cholesterol
 Bile acids
 Sex hormones
 Adrenal hormones
 Vitamin D
Cholesterol
Vitamin D3
Lipid Digestion
 Fats are hydrophobic
 Digestive enzymes are hydrophilic
 Goal of fat digestion
 Dismantle triglycerides into
monoglycerides, fatty acids, and
glycerol
Lipid Digestion
FAT
Mouth and salivary glands
Some hard fats begin to melt as they reach
body temperature. The sublingual salivary
gland in the base of the tongue secretes
lingual lipase.
Salivary
glands
Stomach
The acid-stable lingual lipase initiates lipid
digestion by hydrolyzing one bond of
Gallbladder
triglycerides to produce diglycerides and
fatty acids. The degree of hydrolysis by
lingual lipase is slight for most fats but
may be appreciable for milk fats. The
stomach’s churning action mixes fat with
water and acid. A gastric lipase accesses
and hydrolyzes (only a very small amount
Common
of) fat.
Small intestine
Bile flows in from the gallbladder (via the
common bile duct):
Bile
Fat
Emulsified fat
Pancreatic lipase flows in from the pancreas
(via the pancreatic duct):
Pancreatic
(and intestinal) Monoglycerides,
Emulsified
lipase
fat
glycerol, fatty
(triglycerides)
acids (absorbed)
Large intestine
Some fat and cholesterol, trapped in fiber,
exit in feces.
Mouth
Tongue
Sublingual
salivary gland
Stomach
(Liver)
Pancreatic
duct
Pancreas
bile
duct
Small
intestine
Large
intestine
Fig. 5-12, p. 142
Lipid Digestion
 Mouth- minor
 Lingual lipase for dairy fat
 Stomach- minor
 Strong muscle contractions
 Gastric lipase hydrolyzes TG into
diglycerides and fatty acids
Fat
Watery GI
juices
Enzymes
In the stomach, the fat and
watery GI juices tend to
separate. The enzymes in the GI
juices can’t get at the fat.
Lipid Digestion Main Site
 Small intestine
 Cholecystokinin (CCK) signals
gall bladder to release bile
 Bile acts as emulsifier
 Pancreatic lipases
 Hydrolysis
 Triglycerides and phospholipids
 Bile routes
 Blood cholesterol levels
Bile as an Emulsifier
Bile acid made from cholesterol (hydrophobic)
Bound to an amino acid from
protein (hydrophilic)
Emulsification of Fat by Bile
Fat
Watery GI
juices
Enzymes
In the stomach,
the fat and
watery GI juices
tend to separate.
The enzymes in
the GI juices
can’t get at the
fat.
Enzyme
Fat
Bile
Emulsified
fat
When fat enters
the small intestine,
the gallbladder
secretes bile. Bile
has an affinity for
both fat and water,
so it can bring the
fat into the water.
Emulsified
fat
Bile’s emulsifying
action converts
large fat globules
into small droplets
that repel each
other.
Emulsified
fat
After
emulsification,
more fat is
exposed to the
enzymes, making
fat digestion more
efficient.
Bile acting like Soap
Fat
Bile
Emulsified
fat
Enterohepatic Circulation of Bile
In the gallbladder,
bile is stored.
In the liver,
bile is
made from
cholesterol.
In the small intestine,
bile emulsifies fats.
In the colon, bile that has
been trapped by soluble
fibers is lost in feces.
Enzyme
Emulsified
fat
After emulsification, more fat is exposed
to the pancreatic lipases, making fat digestion
(hydrolysis) more efficient.
Hydrolysis of a Triglyceride
Bonds break
Bonds break
Triglyceride
The triglyceride and two
molecules of water are split. The
H and OH from water complete
the structures of two fatty acids
and leave a monoglyceride.
Monoglyceride + 2 fatty acids
These products may pass into the intestinal
cells, but sometimes the monoglyceride is
split with another molecule of water to give
a third fatty acid and glycerol. Fatty acids,
monoglycerides, and glycerol are absorbed
into intestinal cells.
Lipid Absorption
 Directly into bloodstream
 Glycerol and short- & medium-chain fatty acids
 Micelles- fatty acids, monodiglycerides, bile,
cholesterol diffuse into intestinal cells
 Reassembly of triglycerides from micelles
 Chylomicrons- protein vehicle picking up TG’s,
cholesterol, phospholipids in S.I.
 Intestinal cells release chylomicrons into
lymphatic system
Absorption of Fat
Small intestine
Monoglyceride
Stomach
Short-chain
fatty acids
1
Medium-chain
fatty acids
Glycerol
Micelle
2
Protein
Triglyceride
Chylomicrons
Chylomicron Long-
Capillary
network
Blood vessels
Lacteal
(lymph)
chain
fatty
acids
2 Large lipids such as
monoglycerides and long-chain
fatty acids combine with bile,
forming micelles that are
sufficiently water soluble to
penetrate the watery solution that
bathes the absorptive cells. There
the lipid contents of the micelles
diffuse into the cells.
Via lymph to blood
Via blood to liver
1 Glycerol and small lipids such as short- and medium-chain fatty
acids can move directly into the bloodstream.
Lipid Transport
 Four main types of lipoproteins
 Chylomicrons
 Largest and least dense (more fat, less prot.)
 Shrink as they transport diet-derived lipids
 Liver removes remnants from blood
 Very-low-density lipoproteins (VLDL)
 Made in the liver, 50% TG
 Cells take TG until VLDL becomes LDL
Lipid Transport
 Four main types of lipoproteins
 Low-density lipoproteins (LDL)
 More cholesterol than TG
 Distribute Chol, TG and PL for cell needs
 Liver regulation
 High-density lipoproteins (HDL)
 Made by liver
 Removes cholesterol from cells
 Carry cholesterol to liver for recycling
 Anti-inflammatory properties
Phospholipid
Cholesterol
Triglyceride
100
80
LDL
VLDL
Percent
Chylomicron
Protein
A typical lipoprotein
contains an interior of
triglycerides and
cholesterol surrounded by
phospholipids. The
phospholipids’ fatty acid
“tails” point towards the
interior, where the lipids
are. Proteins near the outer
ends of the phospholipids
cover the structure. This
arrangement of
hydrophobic molecules on
the inside and hydrophilic
molecules on the outside
allows lipids to travel
through the watery fluids of
the blood.
Protein
60
40
Cholesterol
20
Phospholipid
0
Triglyceride
Chylomicron VLDL
LDL
HDL
Chylomicrons contain so little protein and so much
HDL
triglyceride that they are the lowest in density.
Very-low-density lipoproteins (VLDL) are half
This solar system of lipoproteins shows their
triglycerides, accounting for their very low density.
relative sizes. Notice how large the fat-filled
Low-density lipoproteins (LDL) are half cholesterol,
chylomicron is compared with the others and
accounting for their implication in heart disease.
how the others get progressively smaller as their
proportion of fat declines and protein increases. High-density lipoproteins (HDL) are half protein,
accounting for their high density.
Lipid Transport
Role of Triglycerides
 Provide the cells with energy
 9 kcalories per gram
 Virtually unlimited ability to store fat energy in
body
 Adipose tissue secrete adipokines
 regulate energy balance (leptin)
 Insulin resistance and inflammation (resistan)
 Skin insulation, shock absorption, cell
membranes, and cell signaling pathways
Essential Fatty Acids
 Linoleic acid – Omega-6 fatty acid
 Starter for arachidinic acid
 Sources- vegetable oils and meat
 Linolenic acid – Omega-3 fatty acid
 Sources- fish, flaxseed
 Starter for DHA , EPA
 Eicosanoids made from arachidinic and
EPA, regulate blood pressure, clotting
 Fatty acid deficiencies
Lipid Metabolism (Burning Fat)
 Adipose cells store fat after meals
 Lipoprotein lipase in adipose hydrolyzes
triglycerides from lipoproteins passing by
and releases them into adipose cells
 Triglycerides reassembled inside adipose
cells for storage
 Fat supplies 60% of energy during rest
 1 lb body fat = 3500 kcal
 Requires CHO to break down fat
Health Effects of Lipids
 Heart disease
 Elevated blood cholesterol
 Saturated fat – increase LDL cholesterol,
promote blood clotting
 Dietary choices
 Trans-fats – increase LDL cholesterol
 Dietary cholesterol
Health Effects of Lipids
 Heart disease
 Monounsaturated fats
 Replace saturated and trans fats
 Reduces blood cholesterol
 Dietary sources
 Omega-3 fats
 Benefits
 Dietary sources
 Omega-6 to omega-3 ratio
Health Effects of Lipids
 Cancer
 Promotion rather than initiation of cancer
 Dietary fat and cancer risk
 Differs for various types of cancer
 Obesity
 Cutting fat from diet reduces kcalories
 Dietary recommendations
Recommended Intakes of Fat
 DRI and Dietary Guidelines
 Diet low in saturated and trans fat
 Diet low in cholesterol
 20 to 35 percent of daily energy from fat
 AI set for linoleic and linolenic acids
 Daily Values (DV) on food labels
 Saturated fat and cholesterol
 Risk of insufficient fat intake
From Guidelines to Groceries
 Fat-soluble vitamins
 A, D, E, and K
 Flavor, texture, and palatability
 Meats and meat alternatives
 Selections
 Milk and milk products
 Selections
From Guidelines to Groceries
 Vegetables, fruits, and grains
 Lowers consumption of various fats in the
diet
 Invisible fat
 Fried and baked goods
 Choose wisely
 Unprocessed foods
From Guidelines to Groceries
 Fat replacers
 Types
 Risks
 Read food labels
 Total fat, saturated fat, trans fat, and
cholesterol
 Compare products
 % Daily Value vs. % kcalories from fat
Butter and Margarine Labels
Compared
Highlight 5
High-Fat Foods – Friend or Foe?
Guidelines for Fat Intake
 Limit saturated fat and trans fat intake
 Moderate kcalories
 Enough fat for good health
 Not too much of the harmful fats
 DRI recommendations
 Compatible with low rates of disease
High-Fat Foods and Heart
Health
 Olive oil
 Benefits for heart health
 Replace saturated fats
 Nuts
 LDL cholesterol
 Fat composition
 Benefits for heart health
 Cautious advice for dietary inclusion
High-Fat Foods and Heart
Health
 Fish
 Omega-3 fatty acids
 Benefits for heart health
 Environmental contaminants
 Dietary recommendations
High-Fat Foods and Heart
Health
High-Fat Foods and Heart
Disease
 Saturated fat and LDL cholesterol
 Sources of saturated fat in the U.S.
 Meats
 Whole milk products
 Tropical oils
 Zero saturated fat is not possible
 Trans fat
 Limit hydrogenated foods
High-Fat Foods and Heart
Disease
High-Fat Foods and Heart
Disease
High-Fat Foods and Heart
Disease
The Mediterranean Diet
 Traditionally
 Low in saturated fat
 Very low in trans fat
 Rich in unsaturated fat
 Rich in complex carbohydrate and fiber
 Rich in nutrients and phytochemicals
 Benefits for heart disease risk