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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
latrobe.edu.au
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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
fatty acid
glycerol
fatty acid
fatty acid
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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
6
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)
Butyric acid
C4:0
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
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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
o
o
o
o
o
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eggs (430)
lamb brains (2200)
kidney ( 330)
prawns (150)
red meat, chicken (80)
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!
Glucose & energy
2
protein
CHO
acetyl
Co-A
Metabolic
uses 1
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FATTY
ACIDS
3
adipose
tissue (minimal
deposition)
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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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Lipid Transport- Four main types of
lipoproteins
 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
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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
Teaspoons of fat
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
Source: NUTTAB2006
1 teaspoon = 4g fat
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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
4.6
64
Chicken breast (raw)
5.5
66
Milk, whole
3.3
13
trimmed)
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Source: NUTTAB 2006
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Australian versus USA beef
(minced)
Fat content (g fat / 100g edible portion)
Aust
USA
regular
10.8
26.6
premium
up to 10
20.7
extra-trim
up to 7
17.1
Cashel and Greenfield (1995)
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Comparison of meats
Lean steak
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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
Men
AI
13
AI
1.3
AI
160
Women
8
0.8
90
(19-30 yr)
(DHA/EPA/DPA)
mg/d
(19-30 yr)
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-
Weak,
insufficient data
?
depression, mood,
dementia
Obesity
+2
Visual health
possible
?
+3
Vision- age related
macular degeneration
Some good
evidence
2 serves fish /week
+4
Long term antiinflammatory
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
Atlantic salmon *
> 2000
Greenshell/lipped
mussels
950 #
Other Foods
Enriched foods
mg/100g
Varies ^
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
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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.omega3centre.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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Fat Intake and Health
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
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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.
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Thank you
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