Transcript Essential Fatty Acids

The Lipids:
Triglycerides,
Phospholipids, and
Sterols
Chapter 5
Objectives for Chapter 5
1. Recognize the chemistry of fatty acids and triglycerides and differences between saturated and unsaturated fats.
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Describe the structure of a fatty acid and the effects of chain length and saturation on the properties of the fat.
Describe the triglyceride.
List and describe the three types of fatty acids found in foods.
Explain the structure of the omega-3 and -6 fatty acids.
2. Describe the chemistry, food sources, and roles of phospholipids and sterols.
3. Summarize fat digestion, absorption, and transport.
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Trace the digestion of lipids including identification of enzymes needed and the role of bile.
Describe the absorption of lipids into the intestine and the formation of the chylomicron.
Describe the role of the liver in the production of lipoproteins.
Explain the health implications of LDL and HDL and the factors that raise or lower levels of these lipoproteins.
4. Outline the major roles of fats in the body, including a discussion of essential fatty acids and the omega fatty acids.
1. Identify the uses of triglyceride in the body.
2. Identify the essential fatty acids and their role in the formation of eicosanoids.
5. Explain the relationships among saturated fat, trans fat, and cholesterol and chronic diseases, noting
recommendations.
6. Explain the relationships between monounsaturated and polyunsaturated fats and health, noting
recommendations.
7. Identify which fats support health and which impair it.
1. Name practical suggestions for food selections to replace saturated and trans fats with monounsaturated and
polyunsaturated fats.
Introduction
• Poor health
• Too much fat
• Too little fat
• Too much of some kinds of fat
• Family of lipids
• Triglycerides
• Phospholipids
• Sterols
Chemist’s View of Fatty Acids
and Triglycerides
• Energy provided per gram
• More carbons and hydrogens
• Preview of lipids
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Triglycerides: glycerol and 3 fatty acids
Fatty acids: even number of carbons
Fatty acids: saturated or unsaturated
Omega-3 and omega-6 fatty acids
• 18-carbon polyunsaturated fatty acids
Chemist’s View of Fatty Acids
and Triglycerides
• Fatty acids
• Methyl group at one end; acid group at other
end
COOH
H3C
• Usually even number of carbons
• 18-carbon fatty acids abundant in food
• Saturations
• Saturated – full of hydrogens
• Unsaturated – missing hydrogens
18-Carbon Fatty Acids
Yes, I will expect you to know this chart!
Chemist’s View of Fatty Acids
and Triglycerides
• Naming fatty acids
• Location of double bonds
• Nearest the methyl end of the carbon chain
• Omega number
• Monounsaturated fatty acids
• Omega-9 groups (i.e. oleic)
• Polyunsaturated fatty acids
• Linolenic acid = Ω3
• Linoleic acid = Ω6
Omega-3 and Omega-6 Fatty
Acids Compared
Chemist’s View of Fatty Acids
and Triglycerides
• Triglycerides
• Glycerol backbone
• Three fatty acids
• Formed via series of
condensation reactions
• Usually contain mixture
of fatty acids
Condensation of Glycerol and
Fatty Acids to Form a Triglyceride
Chemist’s View of Fatty Acids
and Triglycerides
• Chemistry  Characteristics
• Firmness
• More saturated = more firm
• Longer chain = more firm
• Examples
• Stability
• Oxidation causes spoilage of fats
• More saturated = more stable
• Air-tight, non-metallic, refrigerated,
antioxidants, hydrogenation
Diagram of Saturated & Unsaturated
Fatty Acids Compared
Fatty Acid Composition of
Common Food Fats
Chemist’s View of Fatty Acids
and Triglycerides
• Chemistry  Characteristics
• Hydrogenation
• Advantages: prolongs shelf life, improves
texture (thicker, spreadable, flakey, etc)
• Trans-fatty acids
• Configurations – cis and trans
• Similarity to other types of fat
• Naturally occurring
• Conjugated linoleic acid (CLA)
Hydrogenation
Cis- and Trans-Fatty Acids
Compared
Chemist’s View of
Phospholipids and Sterols
• Phospholipids
• Solubility in fat and water
• Emulsifiers in food industry
• Lecithin (most common)
• Food sources
• Eggs, soybeans, peanuts
• Roles
• Part of cell membranes
• Emulsifiers
Lecithin
Chemist’s View of
Phospholipids and Sterols
• Sterols
• Food sources
• Cholesterol
• Plant sterols
• Roles of sterols
• Body compounds made
from cholesterol
• Bile acids, hormones,
vitamin D, cholesterol
Lipid Digestion
• Fats are hydrophobic
• Digestive enzymes are hydrophilic
• Goal of fat digestion
• Dismantle triglycerides
• Monoglycerides, fatty acids, and glycerol
Lipid Digestion
• Mouth
• Lingual lipase
• Stomach
• Strong muscle contractions
• Gastric lipase
Lipid Digestion
• Small intestine
• Cholecystokinin (CCK)
• Gall bladder releases bile
• Bile acts as emulsifier
• Pancreatic lipase
• Hydrolysis
• Triglycerides and phospholipids
• Bile routes
• Blood cholesterol levels
Fat
Watery GI
juices
Enzyme
Fat
Bile
Emulsified
fat
Enzymes
Emulsified
fat
Emulsified
fat
In the stomach,
the fat and
watery GI juices
tend to separate.
The enzymes in
the GI juices
can’t get at the
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.
Bile’s emulsifying
action converts
large fat globules
into small droplets
that repel each
other.
After
emulsification,
more fat is
exposed to the
enzymes, making
fat digestion more
efficient.
Stepped Art
Figure 5-12 p140
Hydrolysis of a Triglyceride
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.
Stepped Art
Figure 5-14 p141
Lipid Absorption
• Glycerol, short- & medium-chain fatty acids
• Directly into bloodstream
• Monoglycerides, long-chain fatty acids
• Lymphatic system
Lipid Absorption
• Monoglycerides, long-chain fatty acids
• Emulsified = micelle (spherical complex)
• Micelles diffuse into intestinal cells
• Reassembly of triglycerides
• Packed with proteins into chylomicrons
(transport vehicles)  lymphatic system
• Chylomicrons enter bloodstream at thoracic
duct
Absorption of Fat
Lipid Transport
• Transport of lipids through water-based
blood requires transport vehicles
• Four main types of lipoproteins
1. Chylomicrons
• Largest and least dense
• Transport diet-derived lipids
• Liver removes remnants from blood
Lipid Transport
• Four main types of lipoproteins
2. Very-low-density lipoproteins (VLDL)
• Made in the liver
• Proportion of lipid shift as cells remove
triglycerides
3. Low-density lipoproteins (LDL)
• Cells use for energy, make hormones, new
membranes
• Liver regulation – special receptors to get LDL
out of circulation
Lipid Transport
• Four main types of lipoproteins
4. High-density lipoproteins (HDL)
• Remove cholesterol from cells
• Carry cholesterol to liver for recycling
• Anti-inflammatory properties
• Health implications
• LDL linked to heart disease and heart
attacks
• HDL has protective effect
Sizes and Compositions of the
Lipoproteins
Lipid Transport via
Lipoproteins
Role of Triglycerides
• Provide the cells with energy
• Virtually unlimited ability to store fat energy in
body (adipose cells)
• Adipose tissue
• Secretes adipokines (hormones)
• Regulate energy balance
• Type and quantity of secretions change when
body fat is extreme (high or low)
• Skin insulation, shock absorption, cell
membranes, and cell signaling pathways
An Adipose Cell
Essential Fatty Acids
• Must be supplied by the diet
• Linoleic acid (Ω6)
• Linolenic acid (Ω3)
• Can be used to make other
fatty acids
Essential Fatty Acids
• Linoleic acid – Ω6 fatty acid
• Sources: corn, safflower, soybean oils;
walnuts; mayonnaise; pumpkin seeds
• Linolenic acid – Ω3 fatty acid
• Sources: fatty fish; flaxseed; walnuts
• DHA & EPA (linolenic derivatives)
• Essential for normal growth, visual acuity,
cognitive development
• Might: prevention/treatment of heart disease
Essential Fatty Acids
• Eicosanoids (Ω3, Ω6 derivatives)
• “Hormonelike”
• Affect only locally
• Different effects on different cells
• Health benefits
• Ω3: ↓blood pressure, prevent blood clots and
irregular heartbeats, ↓inflammation
• Ω6: promote clot formation, inflammation,
blood vessel constriction (good during injury!);
↓LDL, improve insulin resistance
Essential Fatty Acids
• Ω 6: Ω3 ratio
• Compete, opposite action
• 4:1 to 10:1
• Fatty acid deficiencies
• Infants/children, anorexia nervosa
• Symptoms: growth retardation, reproductive
failure, skin lesions, neurological and visual
problems, kidney/liver disorders
A Preview of Lipid Metabolism
• Adipose cells store fat after meals
• Lipoprotein lipase (LPL)
• Hydrolyzes triglycerides
• Triglycerides reassembled inside adipose
cells
• Using fat for energy
• Protein sparing
• Energy deprivation (fasting)
• Endurance exercise
Health Effects of Saturated Fats,
Trans Fats, and Cholesterol
• Current American diet
• 20% of kcal = solid fats
• Blood lipid profile
• TG, cholesterol, VLDL, LDL, HDL
Health Effects of Saturated Fats,
Trans Fats, and Cholesterol
• Heart disease
• Elevated blood cholesterol
• Saturated fat – ↑LDL cholesterol, promote
blood clotting
• Dietary choices
• 12, 14, 16 carbons vs. 18 carbons
• Meat, milk, milk products
• Trans fats – ↑LDL cholesterol
• Dietary cholesterol
Health Effects of Saturated Fats,
Trans Fats, and Cholesterol
• 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
Recommended Intakes of Saturated
Fat, Trans Fat, & Cholesterol
• DRI and Dietary Guidelines
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20-35% kcal from fat
<10% from sat fat
<1% from trans fat
<300mg cholesterol
• Recommended to consume at least 1 tsp of
fat per meal
Health Effects of Monounsaturated
& Polyunsaturated Fats
• Heart disease
• Replace saturated fats with unsaturated fats
• Regular consumption of omega-3 fatty acids
• Suppress inflammation
• Cancer
• Omega-3 fatty acids from
food
• Supplements
• 1g EPA, 1g DHA
• Can cause excessive bleeding
Replacing Saturated with
Unsaturated Fat
Recommended Intakes of
Mono- & Polyunsaturated Fats
• 20 to 35 percent of kcalories from fat
• Includes essential fatty acids
• AI have been established
• DRI
• Linoleic acid – 5-10% of daily energy
• Linolenic acid – 0.6-1.2% of daily energy
From Guidelines to Groceries
• Fat-soluble vitamins
• A, D, E, and K
• Flavor, texture, and palatability
• Protein foods
• Choose lean cuts, fatty fish, grill/bake/broil
• Milk and milk products
• Choose low-fat/fat-free, fermented
Cutting Fat Cuts kCalories and
Saturated Fat
From Guidelines to Groceries
• Vegetables, fruits, and grains
• Lowers consumption of various fats
• Beware of fried, added fats
• Solid fats and oils
• Fried and baked goods
• Choose wisely
• Unprocessed foods
From Guidelines to Groceries
• Read food labels
• Total fat, saturated fat, trans fat, and
cholesterol
• Compare products
• Fat replacers
• Artificial fats (Olestra)
• Risks: vitamin loss, cramping, loose stool
From Guidelines to Groceries
• Make Heart-Healthy Choices (pg 152)
• Calculating personal Daily Value for Fat
• % DV for fat on food labels = 2000 kcal diet
• Need to translate to YOUR kcal level
• Ex: 1800 kcal, 30% kcal from fat
1800 total kcal X 0.30 from fat = 540 fat kcal
540 fat kcal / 9 kcal/g = 60g fat