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DTN2PNU Principles of Human Nutrition Lecture 7: Fats Lecture Prepared by: Dr Regina Belski & Associate Professor Catherine Itsiopoulos Department of Dietetics and Human Nutrition
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Today
Properties of Fats
Structure of Fats
triglycerides, fatty acids, PMS ratio in food, hydrogenated fats, trans fatty acids
Cholesterol, plant sterols and phospholipids
Digestion and Absorption of Fats
Metabolism of fat and Endogenous fat production
Sources of Fat and Cholesterol in diet
Fat Consumption Patterns in Australia
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Required readings
• Whitney, E., Rolfes, SR, Crowe, T., Cameron-Smith, D. & Walsh, A. (2011). Understanding Nutrition: Australia and New Zealand Edition. South Melbourne, Australia: Cengage Learning Australia.
• CHAPTER 5
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Properties of Fats
Lipids are the components of fat and are characterised by insolubility in water
Lipids exist in 3 main forms in food
triglycerides
95% of lipids in food are found in this form
sterols/plant stanols
e.g. cholesterol , sitosterol
phospholipids
e.g. lecithin
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Structure of Triglycerides
One molecule glycerol to 3 fatty acids
glycerol fatty acid
fatty acid
fatty acid
a. formed from the esterification of 3 fatty acids + glycerol b. the structure and length of the fatty acid determines the state of the fat at room temperature
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Structure of Free Fatty Acids
Organic acid – chain of (4-24) carbon atoms with hydrogens attached
Acid group at one end (COOH) and methyl group at other (CH3)
Foods contain mixture of fatty acids but 18 carbon length most abundant
Length and chemical structure affects stability of fat in foods and solid or liquid state at room temperature
short chain F.As are solid at 250C and long chain liquid
Butyric acid
C4:0
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Saturation of Fats
saturated fatty acids (SFAs) all carbons saturated with single bonds; very stable; mostly solid fats of animal origin; main food sources meat and dairy fat; also in cocoa butter; coconut oil, palm oil; link to endogenous cholesterol production
monounsaturated fatty acids (MUFAs) one double bond; most common oleic acid C18:1n-9 (olive oil); other food sources canola, avocado, peanut oil, most nuts except walnuts
polyunsaturated fatty acids (PUFAs) more than one double bond; least stable; in germ of all grains; food sources safflower, sunflower, sesame, soybean oils
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Naming of fatty acids Saturated
e.g. C18:0 (Stearic acid, found predominantly in beef and lamb & dairy products, palmitic acid C16:0
(found in both plant and animal fats)
Name dependent on location of double bonds
• Nearest the methyl end of the carbon chain
• Omega number
Monounsaturated
e.g. C18:1n-9 (oleic acid, main fatty acid in olive oil) omega 9 or n-9 series
Polyunsaturated
e.g. C18:2n-6 (linoleic acid)
omega 6 or n-6 series
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Sterols (e.g. cholesterol) Endogenous cholesterol
made by the liver (approx 1000 mg/day)
therefore cholesterol is not an essential nutrient
Exogenous cholesterol
from the diet
(approximately 300-400 mg/day)
only found in food of animal origin
cholesterol content (mg /100g) food
o eggs (430)
o lamb brains (2200)
o kidney ( 330)
o prawns (150)
o red meat, chicken (80)
o oysters (80)
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Phospholipid
Solubility in fat and water
e.g. lecithin
not essential as liver manufactures its own lecithin
functions
constituent in cell membranes
component of bile
Used as an emulsifier in food
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Plant sterols and stanols (e.g. sitosterol, sitostanol)
Sources
wood pulp, leaves, nuts, vegetable oils
Actions
interfere with cholesterol absorption by competing with cholesterol for uptake into micelles
has cholesterol-lowering properties
‘new’ margarines
a daily intake of 2-3g of plant sterols reduced LDL cholesterol (‘bad’ cholesterol) by 10-15% (see NHF 2002) and www.heartfoundation.isa.net
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Lipid Digestion
Fats are hydrophobic
Digestive enzymes are hydrophilic
Goal of fat digestion
Dismantle triglycerides
Monoglycerides, fatty acids, and glycerol
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Lipid Digestion
Mouth
Lingual lipase
Stomach
Strong muscle contractions
Gastric lipase
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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
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Lipid Absorption
Directly into bloodstream
Glycerol and short- & medium-chain fatty acids
Lymphatic system
Micelles diffuse into intestinal cells
Reassembly of triglycerides
Packed with proteins – chylomicrons
Bypass liver at first
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Endogenous fat production
Can the body makes it’s own fat without eating fat? yes!
protein
acetyl Co-A CHO
FATTY ACIDS
Metabolic uses
adipose tissue (minimal deposition)
Glucose & energy
1
2
3
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Lipid Transport- Four main types of lipoproteins Chylomicrons
Largest and least dense
Transport diet-derived lipids
Liver removes remnants from blood
Very-low-density lipoproteins (VLDL)
Made in the liver
Proportion of lipid shift
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Low-density lipoproteins (LDL)
Cell needs
Liver regulation
High-density lipoproteins (HDL)
Remove cholesterol from cells
Carry cholesterol to liver for recycling
Anti-inflammatory properties
Lipid Transport- Four main types of lipoproteins
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Role of Triglycerides
Provide the cells with energy
37 kJ per gram
Virtually unlimited ability to store fat energy in body
Adipose tissue
Secretes hormones
Adipokines
Skin insulation, shock absorption, cell membranes, and cell signaling pathways
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Lipid Metabolism
Adipose cells store fat after meals
Lipoprotein lipase
Hydrolyzes triglycerides
Triglycerides reassembled inside adipose cells
Using fat for energy
Protein sparing
Energy deprivation
Fasting and ketone bodies
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Fats in Food
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Finding fat in foods 1 tablespoon oil/ butter 4-5
1 meat pie 6
1 pkt potato chips (50g) 5
3 chicken drumsticks(crumbed) 9
2 chops (untrimmed) 8
2 chops (trimmed) 4
2 slices of salami or bacon 6
1 slice quiche (180g) 12
1 matchbox cube of cheese 2- 3
1 glass full cream milk 2
1 glass Shape or skim trace
1 teaspoon = 4g fat
Teaspoons of fat
Source: NUTTAB2006
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The fat and cholesterol content of common foods (per 100g edible food)
Food Total fat (g) Cholesterol (mg)
Safflower oil 100 0
Butter 80 260
PUFA margarine 80 0
Cheese 30 70
Egg, raw 10.1 375
Brains (raw) 9.4 1,890
Kidney (beef, raw) 2.4 330
Rump steak (raw, fat
trimmed) 4.6 64
Chicken breast (raw) 5.5 66
Milk, whole 3.3 13
Source: NUTTAB 2006
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Australian versus USA beef (minced)
Aust USA
regular 10.8 26.6
premium up to 10 20.7
extra-trim up to 7 17.1
Fat content (g fat / 100g edible portion)
Cashel and Greenfield (1995)
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Comparison of meats
Lean steak Fatty steak
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Where is the fat in Australian diets?
Major contributors of fat to the diet of Australians (ranked)
Meat, poultry and dishes
sausages, chicken skin, salami, takeaway
Cereal based products and dishes
cakes, pastries, biscuits, desserts, takeaway
Milk products and dishes
full-cream milk, cheese, cream, ice-cream, dairy
Fats and oils
butter and margarine (fat spreads)
McLennan & Podger (1998) NNS,1995
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Significance of the P:M:S fatty acid ratio in the food supply
The higher the ratio the better the cholesterol-lowering effect in the population
Ideal 2:1, P+M:S (or 1:1:1; P:M:S)
Australian diet 0.4:1 (NNS 1995)
manipulating animal feed changes the PMS ratio in meat and eggs and milk!
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Hydrogenation of Fat
Chemical process used to “harden” fats to prevent unsaturated fats from rancidity e.g. margarines
Commonly oleic acid (C18:1) and linoleic acid (C18:2) are both converted to stearic acid (C18:0) when fully saturated/hydrogenated.
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Problems with Hydrogenation
no control over which double bonds are broken
formation of trans fatty acids (isomers)- naturally found in very small amounts in nature
o For example oleic acid converted to its isomer, elaidic acid
o Elaidic acid mimics the physical and physiological properties of saturated fat
o trans fatty acids considered equivalent to saturated fat re: increasing CVD risk
In 1996 in Australia, trans fatty acids were removed from margarines derived from plant oils
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Are fatty acids essential to the body?
Yes - Only 2 fatty acids are essential
linoleic acid c18:2n-6
Food sources – vegetable oils, red meat, nuts, seeds
Omega-6 fatty acid
Alpha-linolenic acid c18:3n-3
Food sources – canola, flaxseed, soybean, walnuts, grren vegetables
Omega-3 fatty acid
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NRVs for essential fats
Linoleic acid (n-6) g/d
α-linolenic (n-3)
g/d
LC-n3 (DHA/EPA/DPA)
mg/d
AI AI AI
Men (19-30 yr)
13 1.3 160
Women (19-30 yr)
8 0.8 90
DHA – docosahexanoic acid (C22:6:3), EPA- eicosapentanoic acid (C20:5:3),
DPA - docosapentaenoic acid - long chain (C22:5:3)
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Why are long chain (C22) fatty acids important?
Rank Area Strength of evidence
Dosage
+1 Mental health- depression, mood, dementia
Obesity
Weak, insufficient data
?
+2 Visual health possible ?
+3 Vision- age related macular degeneration
Some good evidence
2 serves fish /week
+4 Long term anti-inflammatory
Conclusive evidence
3g/D EPA+ DHA (fish oil capsules)
+4 Cardiovascular disease Conclusive evidence
500mg/d EPA+ DHA = 2-3 serves oily fish/w - Prevention
1g/d EPA+ DHA - Treatment
Scientific consensus workshop 2008
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Food sources of omega 3 fatty acids
Seafoods mg/100g Other Foods mg/100g
Atlantic salmon * > 2000 Enriched foods Varies ^
Greenshell/lipped
mussels
950 # Eggs regular 80
Hoki (Blue grenadier) 410 Turkey 30
Gemfish 400 Beef 20
Blue eye cod 310 Milk regular 0
Sydney rock oysters 300 Vegetable oils &
spreads
0
Tuna canned 230 Regular bread 0
Snapper 220 Cereals, rice, pasta,
etc
0
Barramundi saltwater 100 Fruit 0
Giant tiger prawn 100 Vegetables 0
Source: Fatty acid database, RMIT University
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Recommended intake to meet the SDT (suggested Dietary targets) for long chain fatty acids (C22)
2-3 serves oily fish /week
Fish oil or capsules
Food and drinks enriched with MARINE omega 3 fatty acids
Omega 3 centre in Australia http://www.omega-3centre.com/index.html
Scientific Consensus Workshop Omega 3 fatty acids, October 2008
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Lipids- Recommended Intakes
For most adults dietary fat should provide at least:
15% of total energy
20% for women of reproductive age
Also need to consider:
Essential fatty acids
Fat-soluble vitamins
Upper limit of fat intake:
Ideally <30% of total energy
Sat fat <10% total energy
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Fat Intake and Health
Heart disease
Elevated blood cholesterol
Saturated fat – increase LDL cholesterol, promote blood clotting
Trans-fats – increase LDL cholesterol
Monounsaturated fats
Should Replace saturated and trans fats
Reduces blood cholesterol
Omega-3 fats
Omega-6 to omega-3 ratio is important
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Cancer
Promotion rather than initiation of cancer
Dietary fat and cancer risk
Differs for various types of cancer
Obesity
Cutting fat from diet reduces energy intake
Fat Intake and Health
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References
Howe, PRC, Meyer, BJ, Record, S, Baghurst K. Dietary intake of long chain omega-3 polyunsaturated fatty acids. Contribution of meat sources. Nutrition 2006;22;47-53
NHFA. Position statement fish oils, NHF of Australia 2008
NUTTAB2006
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Image Sources
The images used in this presentation are from www.office.com, or the presenters own, unless otherwise attributed.
Thank you
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