Dietary Fat

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Lecture 8 Dietary Fat Health
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Fatty Acids

• HYDROGENATION
• adding of hydrogen atoms to a polyunsaturated or
  monounsaturated fat
• makes the fat more saturated
• makes the fat more solid
• (? more spreadable)

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Trans Fatty Acids

• partial hydrogenation of polyunsaturated FA
• produces trans-fatty acids
• relationship between heart disease trans -
  fatty acids?
• Ascherio Willett, 1997.
• Health effects of trans Fatty acids
• AJCN, 66(suppl.), 1006S-1010S.

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Trans Fatty Acids
Food Examples

• Naturally occurring
• milk
• butter

• Manufactured
• some margarines
• cakes biscuits
• potato crisps
• peanut butter
• fish chips

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Essential fatty acids

• indispensable to body function
• cannot be synthesised
• must be supplied in the diet
• 2 CANNOT be synthesised
• they are polyunsaturated FA
• all other FA CAN be synthesised

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Required for

• Phospholipids
• cell membrane fat
• synthesis of other polyunsaturated fatty acids
  (PUFA)
• desaturation elongation

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Essential fatty acid Linoleic Acid

• 18 carbon atoms
• an Omega 6 fatty acid

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Essential fatty acid Linolenic Acid

• 18 carbon atoms
• an Omega 3 fatty acid

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Omega-6 Omega-3 fatty acids

• Omega (?)
• refers to position of end most DOUBLE bond in a
  fatty acid
• Omega-6
• first double bond is 6 carbons from the methyl
  (CH3) end of the carbon chain

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? -6 ? -3 fatty acids

• Omega-3
• first double bond is 3 carbons from the methyl
  end

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Omega-6 Omega-3 fatty acids
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Dietary Sources Linoleic Acid (?-6)

• vegetable oils
• Safflower Sunflower
• soybean
• corn

• vegetable seeds
• nuts
• grains

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Dietary Sources ?-Linolenic Acid (?-3)

• wheat germ
• margarine
• canola
• soybean

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Omega-6 Omega-3 fatty acids

• Linoleic Acid
• ?-6 fatty acid
• 18 carbon atoms
• precursor to other ?-6 fatty acids for eicosanoid
  synthesis
• eg. prostaglandin, thromboxane

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Omega-6 Omega-3 fatty acids

• Linolenic Acid
• ?-3 fatty acid
• 18 carbon atoms
• precursor to other ?- 3 fatty acids
• eg. EPA (205) fish oils
• DHA (226)

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Fat Digestion
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Fat Digestion

• SOME (minor) gastric digestion of fat
• Lingual lipase Gastric lipase
• begins triglyceride digestion
• only short medium chain fatty acids
• MOST fat digestion in small intestine

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Fat Digestion

• fats require EMULSIFICATION
• BILE ACIDS emulsify
• digestion in SMALL INTESTINE (Duodenum)
• 95 digestion absorption of dietary Fat

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Fat Digestion Triglycerides

• pancreas also releases LIPASE
• splits Triglycerides into
• free fatty acids
• di-glycerides
• mono-glycerides
• glycerol

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Splitting of Triglycerides

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Fat Digestion Phospholipids

• digested by PHOSPHOLIPASE
• HYDROLYSIS reaction

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Fat Digestion Cholesterol

• no prior digestion
• absorbed whole

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Dietary fatAbsorption
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Fat Absorption Triglycerides

• monoglycerides (triglyceride backbone) long
  chain fatty acids (? 20 carbon atoms)
• must form MICELLES before absorption
• glycerol, short medium chain fatty acids
  absorbed DIRECTLY

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MICELLES

• FIG 5-16 WHITNEY ROLFES

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Post-absorption

• TRIGLYCERIDES
• intestinal cells re-assemble monoglycerides
  fatty acids into Triglycerides release into
  bloodstream
• Triglycerides picked up by CHYLOMICRONS in
  bloodstream

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Post-absorption

• Phospholipids Cholesterol
• also picked up by Chylomicrons
• most (Triglycerides, Phospholipids Cholesterol)
  travel to liver via the LYMPH system

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Recommended reading

• 1. Whitney Rolfes
• Understanding Nutrition
• Chapter 5. The Lipids Triglycerides,
  Phospholipids Sterols
• 2. Ascherio, A. Willett, W.C. (1997).
• Health effects of trans Fatty acids
• AJCN, 66(suppl.), 1006S-1010S.
• Homepage e-reader

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Recommended reading

• 3. Wahlqvist
• Food and Nutrition in Australia
• Chapter 18. Lipids