The Lipids: Triglycerides,
Phospholipids, and Sterols
Chapter 5
Introduction
• Poor health from fat consumption is seen
when a person consumes either
• Too much fat
• Too little fat
• Too much of some kinds of fat
• Lipids = Fat
– Family of lipids
• Triglycerides (TG) (fats & oils)*
• Phospholipids
• Sterols
Chemist’s View of Fatty Acids and
Triglycerides
• Lipids =
– TG, Phosolipids, and sterols
• Composed of C, H, and O
• Have more C & H = supply more E per gram
• Most are TG w/ glycerol backbones and
three fatty acids (f.a.)
Chemist’s View of Fatty Acids and
Triglycerides
• F.A. vary in C chain lengths, degree of
unsaturation, and # of double bonds (d.b.)
• Trans-fatty acids
Chemist’s View of Fatty Acids and
Triglycerides
 Preview of lipids
 Triglycerides: glycerol and 3 fatty acids
 Fatty acids: even number of carbons
 4-24Cs; 18C most common in foods
 Saturated or unsaturated
 Mono or polyunsaturated
Chemist’s View of Fatty Acids and
Triglycerides
• Fatty acids
– Organic acid
– Methyl group (CH3) at one end; acid group
(COOH) at other
– Usually even number of Cs
– Saturation
Chemist’s View of Fatty Acids and
Triglycerides
• Unsaturated
– Monounsaturated f.a. :
• Lack 2H atoms & have 1 d.b.
• When most of the f.a.s are monounsat its called a
monounsaturated fat
– Polyunsaturated f.a.s (PUFA)
• Lack 4 or more Hs & have at least 2 or more d.b.
• When most of the f.a.s are polyunsaturated its called
a polyunsaturated fat
Chemist’s View of Fatty Acids
Location of d.b.
 Nearest the methyl end of the carbon chain
 Assigned an Omega number
 Omega- 3-polyunsat f.a.
 Linolenic acid are essential f.a.
» Soybean and canola oils, flaxseed, walnuts
 Omega- 6-polyunsat f.a.
 Linoleic acids are essential f.a.
» Vegetable, i.e. sunflower, safflower, corn, and soy bean oils
 Monounsaturated fatty acids
 Omega-9 groups
• Oleic acid most predominate in diet
• Olive, canola oils
Chemist’s View of Fatty Acids and
Triglycerides
• Triglycerides
– Three fatty acids attached to Glycerol backbone
– Formed via series of condensation reactions
– Usually contain mixture of fatty acids
Chemist’s View of Fatty Acids and
Triglycerides pg 137
Chemist’s View of Fatty Acids and
Triglycerides
• Degree of unsaturation
– Firmness
• Polyunsaturated fats
• Saturated fats
• Length of carbon chain
– Stability
•
•
•
•
Sat fat is more resistant to oxidation
monounsat fat is slightly less susceptible to spoilage
Polyunsat fat spoils most readily
Protection from rancidity:
Chemist’s View of Fatty Acids and
Triglycerides
• Degree of unsaturation
– Hydrogenation
– Trans-fatty acids
Chemist’s View of Fatty Acids and
Triglycerides
Chemist’s View of Fatty Acids and
Triglycerides
Chemist’s View of Phospholipids
and Sterols
• Phospholipids
– Contain glycerol, 2 f.a. and a phosphate group
with a molecule of choline
– Solubility in fat and water
– Emulsifiers in food industry
– Roles
Chemist’s View of Phospholipids
and Sterols
• Sterols
– Food sources
• Cholesterol
• Plant sterols
– Roles of sterols
• Starting material for bile acids, sex hormones,
adrenal hormones, and vit. D
• Structural component of cell membranes
• Liver produces 800-1500mg cholesterol per day
• Atherosclerosis
Lipid Digestion
 Fats are hydrophobic
 Tend to separate from watery fluids in GI tract
 Digestive enzymes are hydrophilic
 Goal of fat digestion
 Dismantle triglycerides for body to absorb and
use
Lipid Digestion
• Mouth
– Lingual lipase released by salivary glands
• Stomach
– Strong muscle contractions disperse fat into
smaller droplets
– Fat then exposed to Gastric lipase
Lipid Digestion
• Small intestine
– Cholecystokinin (CCK)
– Pancreatic and intestinal enzymes
– Phospholipids are hydrolyzed
– Sterols are absorbed
– Bile routes
– Enterohepatic circulation
– Soluble fibers are effective
• in trapping some bile and
• excreting it from the body thru the large intestine
Emulsification of Fat by Bile
Hydrolysis of a Triglyceride
Enterohepatic Circulation of Bile
Lipid Absorption
• Directly into bloodstream
– Glycerol and short- & medium-chain fatty acids
diffuse and are re-absorbed directly into the
bloodstream
• Lymphatic system
– Larger molecules, Monoglycerides and long-chain
f.a.s, form micelles that get reabsorbed, and are
reformed into new triglycerides. With protein they
are transported by chylomicrons
– When packaged with protein it’s then transported
so that cells all over body may select needed lipids
Lipid Transport
 Lipid transport is made possible by a group of
vehicles known as lipoproteins
 Four main types of lipoproteins
Chylomicrons
Very-low-density lipoproteins (VLDL)
Low-density lipoproteins (LDL)
High-density lipoproteins (HDL)
Health implications
• High LDL is associated with higher risk of heart attack
and is known as a “bad” cholesterol
• High HDL seems to have a protective effect and is
known as “good” cholesterol
• Factors that lower LDL and raise HDL
• Genes influence lipopro activity
Role of Triglycerides
• Provide the cells with energy
– 9 kcalories per gram
• Adipose tissue
– Virtually unlimited ability to store fat energy in
body
– Secretes hormones
• Skin insulation, shock absorption, cell
membranes, and cell signaling pathways
Essential Fatty Acids
• Linoleic acid – Omega-6 fatty acid
• Linolenic acid – Omega-3 fatty acid
– EPA & DHA-important for eyes, brain, and
heart
• Fatty acid deficiencies
– Rare in US and Canada
– Occur in infants and children with fat-free or
low-fat diets
A Preview of Lipid Metabolism
• Adipose cells store fat after meals
– Lipoprotein lipase
– Triglycerides reassembled inside adipose cells
• Using fat for energy
– Hormone-sensitive lipase inside the adipose cells
hydrolyzes TG when needed for E
– During fasting the body metabolizes fat, but
requires CHO and pro for complete fat
breakdown
– Ketone bodies can be made from fat fragments
Health Effects of Lipids
• Heart disease
– Elevated blood cholesterol
•
•
•
•
Saturated fat
Dietary choices
Trans-fats
Dietary cholesterol
Health Effects of Lipids
• Heart disease
– Monounsaturated fats
• Replace saturated and trans fats
• Reduces blood cholesterol
• Dietary sources
– Omega-3 fats
• Benefits
• Dietary sources
• Omega-6 to omega-3 ratio
Health Effects of Lipids
• Cancer
– Promotion rather than initiation of cancer
– Dietary fat and cancer risk
• Obesity
– Cutting fat from diet reduces kcalories
Recommended Intakes of Fat
 DRI and Dietary Guidelines
Diet low in saturated and trans fat
Diet low in cholesterol
20 to 35 percent of daily energy from fat
 AI set for linoleic and linolenic acids
 Daily Values (DV) on food labels
Saturated fat and cholesterol
 Risk of insufficient fat intake
From Guidelines to Groceries
• Very lean and lean options of meat and meat
alternative products
• Fat-free and low-fat milk products
• Wide variety of vegetables, fruits, and whole grains
• Avoid invisible fat from high-fat cheese, baked &
fried goods
• Choose wisely from many available food products
From Guidelines to Groceries
 Fat replacers
Ingredients derived from CHO, pro, or fat
Replace fat in foods
Artificial fats offer sensory and cooking qualities but no
kcalories.
 Research on olestra supports its safety but it decreases the absorption
of fat-soluble vits and may cause digestive distress in some
 Read food labels
Total fat, saturated fat, trans fat, and cholesterol
Compare products
% Daily Value vs. % kcalories from fat