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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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