The Lipids:
Triglycerides,
Phospholipids, and
Sterols
Chapter 5
Why do we need it?

Fat provides…
 Ability to absorb fat-soluble vitamins A,
D, E, and K
 Flavor, texture, and palatability
 Increased satiety
 Essential nutrients: the essential fatty
acids (EFA)
Fat and Health

Fat intake and health issues
 Too much fat
 Too little fat
 Too much of some kinds of fat

Lipid family
 Triglycerides
 Phospholipids
 Sterols
Chemist’s View of Fatty Acids
and Triglycerides

Energy provided per gram: 9 kcals
 More carbons and hydrogens

Lipid Structure
 Triglycerides: Major lipid in foods
 Glycerol and 3 fatty acids
 Fatty acids: even number of carbons
 Fatty acids: saturated or unsaturated
Structure of a Triglyceride
Triglyceride
Triglyceride Condensation
Characteristics of Fatty Acids

Organic acid
 Methyl group at one end (omega end)
 Acid group at other end

Usually even number of carbons
– Vary in length from a few to 20 or more carbons
– Short-chain fatty acids: 4-7 carbons
– 18-carbon fatty acids abundant in food

Saturation
 Saturated – full of hydrogens
 Unsaturated – missing hydrogens
Saturated Fatty Acid
Stearic acid
Monounsaturated Fatty Acid
Polyunsaturated Fatty Acid
Docosahexaenoic Acid (DHA)
Double Bonds

Fatty acids
 Location of double bonds
 Numbered starting with bond nearest the
methyl end of the carbon chain
 Omega number
 Linolenic acid: omega-3
 Monounsaturated fatty acids
 Omega-9 groups
Effects of Double Bonds

Degree of unsaturation
 Firmness
 Polyunsaturated fats
 Saturated fats
 Length of carbon chain

Fatty acid structure and stability
 Oxidation and spoilage of fats
 Influences
 Antioxidants in oils
Structure and Physical
Properties of Fatty Acids

Polyunsaturated fats vs. saturated fats
 “Vegetable oils” are cheap for manufacturers,
but vulnerable to oxidation (spoilage)
 Solution: hydrogenation
 Advantages
 Disadvantages
 Trans-fatty acids
 Configurations – cis and trans
 Trans: implicated in a growing number of
disorders and illnesses - inflammation
Transfatty acid
Essential Fatty Acids

Linoleic acid – Omega-6 fatty acid
 Sources
 AA (arachidonic acid)

Linolenic acid – Omega-3 fatty acid
 Sources
 ALA
 DHA
 EPA
 Cell membrane structure, eicosanoids
EFA: Metabolic Pathways
Omega-3 vs. Omega-6
Both essential fatty
acids
 Americans tend to get
lots of n-6, not so much
n-3
 Eicosanoids made from
n-3: anti-inflammatory

• Eicosanoids made from
n-6: pro-inflammatory
Eicosanoids from Omega-3 and
Omega-6 Fatty Acids
Essential Fatty Acid Deficiency

Frank deficiency is rare
–
–
–
–
Scaly, dry skin
Liver abnormalities
Poor wound healing
Impaired growth and neurological development in
infants, young children
– Impaired vision and hearing

Suboptimal levels
– Possible disorders affecting mood, cognition, and
memory
– Inflammatory conditions
• Skin
• Cardiovascular system
• Joints
Phospholipids and
Sterols
Phospholipids

Phospholipids
 Solubility in fat and water
 Emulsifiers in food industry
 Lecithin
 Food sources
 Roles
 Part of cell membranes
 Emulsifiers
Phospholipid Bilayer
Sterols

Cholesterol
Sterols
 Food sources
 Cholesterol
 Plant sterols

Roles of sterols
 Body compounds made from cholesterol
Lipid Digestion

Fats are hydrophobic
 Digestive enzymes are hydrophilic
 Digestive juices are watery
 Need bile to emulsify fats

Goal of fat digestion
 Dismantle triglycerides
 Monoglycerides, fatty acids, and glycerol
Hydrolysis of a Triglyceride
Lipid Digestion

Mouth
 Lingual lipase

Stomach
 Strong muscle contractions
 Gastric lipase

Most of the action occurs in the small
intestine
Lipid Digestion

Small intestine
 Cholecystokinin (CCK) released
 Stimulates gall bladder to release bile
 Bile acts as emulsifier
 Pancreatic lipase
 Hydrolysis
 Triglycerides and phospholipids

Bile routes
 Blood cholesterol levels
Fat
Watery GI
juices
Enzymes
In the stomach,
the fat and
watery GI juices
tend to separate.
The enzymes in
the GI juices
can’t get at the
fat.
Enzyme
Fat
Bile
Emulsified
fat
When fat enters
the small intestine,
the gallbladder
secretes bile. Bile
has an affinity for
both fat and water,
so it can bring the
fat into the water.
Emulsified
fat
Bile’s emulsifying
action converts
large fat globules
into small droplets
that repel each
other.
Emulsified
fat
After
emulsification,
more fat is
exposed to the
enzymes, making
fat digestion more
efficient.
Stepped Art
Fig. 5-14, p. 143
In the gallbladder,
bile is stored.
In the liver,
bile is
made from
cholesterol.
In the small intestine,
bile emulsifies fats.
In the colon, bile that has
been trapped by soluble
fibers is lost in feces.
Stepped Art
Fig. 5-16, p. 144
Lipid Absorption

Directly into bloodstream
 Glycerol and short- & medium-chain fatty
acids

Lymphatic system
 Micelles diffuse into intestinal cells
 Reassembly of triglycerides
 Packaged with proteins – chylomicrons
 Bypass liver at first
Lipid Transport


Four main types of lipoproteins
Provide triglycerides, cholesterol, and
phospholipids for cells
 Build new membranes
 Make hormones or other
compounds
 Storage
Lipoproteins

Chylomicrons
 Largest and least dense
 Transport diet-derived lipids (mostly TG)
 Taken up by cells
 Liver removes remnants from blood
 Very-low-density lipoproteins (VLDL)
 Made in the liver from chylomicron
remnants
 Released to rest of body
 Cells take up TG, leaving cholesterol
Lipoproteins

Low-density lipoproteins (LDL)
 Contain lots of cholesterol; also TG and
phospholipids
 Circulate cholesterol to the body’s cells

High-density lipoproteins (HDL)
 Remove cholesterol from cells
 Carry cholesterol to the liver for recycling
 Anti-inflammatory properties

Health implications
Lipid Transport
Cardiovascular Disease

Over 80 million Americans suffer from some
form of cardiovascular disease
 Studies show that diet and lifestyle affect the
risk of developing cardiovascular disease
– Disagreement about the specifics!
– Increasing evidence implicates diets high in
refined CHO and low in fiber, antioxidants, and
omega-3 fats

Atherosclerosis is a disease in which lipids
and fibrous materials are deposited in artery
walls
Lipid Functions in the Body

Most lipids in the body are triglycerides stored
in adipose tissue, which helps to…
–
–
–
–

Define body shape
Provide stored energy
Insulate the body from temperature changes
Protect internal organs against physical shock
Lipids are also important for lubricating body
surfaces, such as the skin, hair, and the
mucous membranes of the eyes
More Functions of Lipids

Cholesterol is used to make several
hormones, including estrogen and
testosterone.
 Essential fatty acids are important for growth,
skin integrity, fertility, the structure and
function of cell membranes, and making
eicosanoids
 Eicosanoids help regulate blood clotting,
blood pressure and immune function.
 Fatty acids and glycerol can be used to
produce energy in the form of ATP.
Fatty Acid
Oxidation:
Energy
from fats
Energy from
Fats