The science of nutrition 4th edition thompson manore vaughan chapter 05

Chapter 5 Lecture

Chapter 5:
Lipids: Essential
Energy-Supplying
Nutrients

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What Are Lipids?
• Lipids
• Diverse group of molecules that are insoluble
in water
• Fats
• The lipid content of diets and foods

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What Are Lipids? (cont.)
• Three types of lipids are found in foods and in
body cells and tissues:
• Triglycerides
• Phospholipids
• Sterols

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Triglycerides

• Triglycerides (also called triacylglycerols)
contain:
• Three fatty acid molecules
• One glycerol molecule

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Triglycerides (cont.)
• Fatty acids are classified by the type of fatty
acids attached to the glycerol backbone.
• Fatty acids can vary by:
• Carbon chain length
• Saturation level
• Shape

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Triglycerides: Chain Length
•
•
•
•

Short-chain fatty acid (< 6 carbon atoms)
Medium-chain fatty acid (6–12 carbon atoms)
Long-chain fatty acids (≥14 carbon atoms)
Carbons can be numbered
• Carboxyl end (COOH): α-carbon (alpha—first)

• Methyl end (CH3): Ω-carbon (omega—last)

• Fatty acid chain length determines method of
lipid digestion, absorption, metabolism, and use

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© 2017 Pearson Education, Inc.


Triglycerides: Saturation
• Saturated fatty acids have hydrogen atoms
surrounding every carbon in the chain (no
double bond)
• Monounsaturated fatty acids lack one hydrogen
atom (one double bond)
• Polyunsaturated fatty acids have more than
one double bond

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Triglycerides: Shape
• Level of saturation affects fatty acid shape
• Saturated fatty acids form straight, rigid chains,
packed tightly together.

• Saturated fatty acids are solid at room
temperature
• Animal fats, butter, and lard are high in
saturated fatty acids

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Triglycerides: Shape (cont.)
• Unsaturated fatty acids have kinked fatty acids
at double bond and do not pack together tightly
• Unsaturated fatty acids are liquid at room
temperature
• Hydrogen atoms can be arranged in different
positions at the point of unsaturation:
• Cis: same side of the carbon chain
• Trans: opposite sides of the chain

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© 2017 Pearson Education, Inc.


Triglycerides
• Hydrogenation: hydrogen atoms are added to
unsaturated fatty acids

• Make oils more solid and more saturated
• Create trans fatty acids
• Helps food reduce oxidation and resist
rancidity
• Increase risk of cardiovascular disease

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Triglycerides (cont.)
• Essential fatty acids: cannot be made by the
body and must be obtained from food
• Precursors to eicosanoids which regulate cell
function
• Linoleic acid (omega-6 fatty acid)
• Found in vegetable and nut oils
• Alpha-linolenic acid (omega-3 fatty acid)
• Found in vegetables, soy, flaxseeds, walnuts

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© 2017 Pearson Education, Inc.


© 2017 Pearson Education, Inc.


Triglycerides (cont.)
• Omega-3 fatty acids found in fish and fish oil

• Eicosapentaenoic acid (EPA)
• Docosahexaenoic acid (DHA)
• Protect against cardiovascular disease
• Stimulate prostaglandins and thromboxanes
that reduce inflammatory responses
• Reduce blood clotting and plasma
triglycerides

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Phospholipids
• Phospholipids contain
• Glycerol backbone
• Two fatty acids
• Phosphate
• Soluble in water
• Assist in transporting fats in the bloodstream
• Lecithins combine with bile salts and electrolytes
to make bile
• Manufactured in our bodies (not required)

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Sterols
• Sterols contain multiple rings of carbon atoms

• Plant sterols appear to block the absorption of
dietary cholesterol
• Cholesterol is found in animal-based foods as
cholesterol esters.
• Cholesterol is made in in the liver and is not
necessary in the diet
• Is used to make hormones, vitamin D, bile

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Digestion of Fats
• Fat digestion begins in the small intestine
• Cholecystokinin (CCK) and secretin: gallbladder
contractions release bile
• Bile is produced by the liver and stored in the
gallbladder
• Bile emulsifies fat into small droplets
• Pancreatic enzymes break fat into two fatty
acids and a monoglyceride

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© 2017 Pearson Education, Inc.

Absorption of Fats
• Micelles capture lipid digestion products and
transport them to the enterocyte for absorption
• Lipoproteins transport lipids into the
bloodstream
• Chylomicrons are lipoproteins produced in the
enterocyte to transport lipids from a meal
• Composed of fatty acids surrounded by
phospholipids and proteins
• Soluble in water

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