Chapter 5: Lipids

Overview

� Structure: Saturated vs non-saturated FA� Classification: Essential vs non-essential� Classes: TG, phospholipids, sterols� Functions� Digestion and absorption� Transport� Foods and diet patterns

Lipids

� Do not readily dissolve in water� Fats are solid at room temperature� Oils are liquid at room temperature� Triglycerides are the main form of lipids in

food and body (storage)� Energy dense (9 kcal /gm)

Fatty Acids

� Building blocks of lipids� Saturated� Unsaturated

� Monounsaturated� Polyunsaturated

Fatty Acid Structure

Methyl group Acid group(omega end) (alpha end) degree of saturation

H H H H H H H H H H H H H H H H H O

H-C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C-OH

H H H H H H H H H H H H H H H H H

Saturated Fatty Acid Structure

Methyl group Acid group(omega end) (alpha end) Saturated Fatty Acid C18:0

H H H H H H H H H H H H H H H H H O

H-C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C-OH

H H H H H H H H H H H H H H H H H

Monounsaturated Fatty Acid Structure

Methyl group Acid group(omega end) (alpha end)

One double bond C18:1

H H H H H H H H H H H H H H H O

H-C--C--C--C--C--C--C--C--C=C--C--C--C--C--C--C--C--C-OH

H H H H H H H H H H H H H H H H H

Polyunsaturated Fatty Acid Structure

Methyl group Acid group(omega end) (alpha end)

> 2 double bonds C18:2

H H H H H H H H H H H H H O

H-C--C--C--C--C--C=C--C--C=C--C--C--C--C--C--C--C--C-OH

H H H H H H H H H H H H H H H H H

Chain Length & Saturation: Fatty Acid Characteristics

� Long chain…> 12 C� Medium chain …6-10 C� Short chain…< 6 C

� Saturated � Unsaturated

Unsaturated Fats

� Fewer H atoms; double bonds between Carbons� Usually liquid at room temp� Mostly plant and fish sources� More chemically active (turn rancid faster)� Lower blood cholesterol� Monounsaturated fat (MUF) - 1 double bond

(minus 2 H)� Polyunsaturated fat (PUF) - 2 or more double

bonds

Saturated Fats

� Maximum # of Hydrogen atoms� Usually solid at room temp.� Mostly from animal sources (meat & dairy)� Exceptions - tropical oils (palm, coconut)

very saturated� Raise blood cholesterol

Essential Fatty Acids

� Cannot be produced by the body� Omega-3 & Omega-6 fatty acids

� Essential for immune function, vision, cell membrane, and production of hormone-like compounds

Essential Fatty Acid- Omega-3 (alpha-linolenic acid)

omega end alpha end 1st double bond is located on the 3rd carbon

from the omega end

H H H H H H H H H H H H H H H H H O

H-C--C--C=C--C--C =C--C--C=C--C--C--C--C--C--C--C--C-OH

H H H H H H H H H H H

Omega-3 Fatty Acid

� Fish oil is important source� Also found in canola, soybean oil & nuts� Eicosapentaenoic acid (EPA) and

docosahexaenoic acid (DHA)� Recommendation: eat fish 2 x per week� Decreases blood clot formation� Lowers risk of heart disease

Essential Fatty Acid- Omega-6 (alpha-linoleic acid)

omega end alpha end 1st double bond is located on the 6th carbon

from the omega end

H H H H H H H H H H H H H O

H-C--C--C--C-- C--C =C--C--C=C--C--C--C--C--C--C--C--C-OH

H H H H H H H H H H H H H H H H H

Omega-6 Fatty Acid

� Found in vegetable oils� Arachidonic acid

� Need about 1 tablespoon daily� Increases blood clotting� Increases inflammatory responses

Signs and Symptoms of Essential Fatty Acids Deficiency

� Flaky, itchy skin� Diarrhea� Infections� Growth retardation � Poor wound healing� Anemia

Functions of Lipids

� Concentrated energy (diet and storage)� Provides essential FAs� Insulation for body � Padding around organs� Transport fat-soluble vitamins� Contribute to satiety� Flavor and mouth feel of foods� Present in cell membranes

Triglycerides (TGs)

� Most lipids in foods and body in form of TGs (95%)

� Chemical structure:� Glycerol back bone� 3 fatty acids (Fas)� FA 4-22 C long; usually 16-20 C

Triglycerides

(condensation reaction) Glycerol + 3 FA’s Triglyceride +

3 H20

H

H--C--O—H

H--C--O—H

H--C--O—H

H

Fatty Acid

Fatty Acid

Fatty Acid

+

H O

H--C--O--C--

O

H--C--O--C--

O

H--C--O--C--

H

Fatty Acid

Fatty Acid

Fatty Acid

Triglycerides

Function of Triglycerides

� Concentrated energy (diet and main storage form)� Provides essential fatty acids (linoleic; linolenic)� Carrier of Fat Soluble Vits (A,D,E,K)� Body Insulation & padding around organs� Cell membranes� Adds flavor & texture to foods� Contributes to satiety

Phospholipids

� Built on glycerol backbone� > 1 FA replaced with P containing

compound� Cell membranes� Help transport other fats in blood� Emulsifier in foods� Mix with both water and fat

Chemical forms of Phospholipid

Sterols

� Multi-ringed structures; noncaloric

� Do not dissolve in water well

� ex. cholesterol & Vitamin D

Two sterols

Function of Cholesterol

� Cell membranes� Precursor for Vit D & some hormones (estrogen,

testosterone)� Major component of bile� ONLY FOUND IN ANIMALS; NEVER FOUND

IN PLANTS� Not an essential nutrient since it’s made in body� Produced by the liver

Cell membranes