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Chapter 5
Lipids:
Not Just Fat
What Are Lipids?
• Essential nutrients
– Provide energy
– Help transport fat-soluble nutrients
throughout the body
• Contribute greatly to the flavor and texture of
food
Lipids Include…
• Triglycerides (most abundant lipids)
– In body: stored in adipose tissue
– In food: “fats and oils”
• Phospholipids (~2% of dietary lipids)
– Plant and animal origin
– Body can make them
– Soluble in fat and water
• Sterols (very, very small % of lipids)
– Most well known: Cholesterol
Fatty Acids Are Key Building Blocks
• Fatty acid
– Determines
whether a fat is
solid or liquid at
room temperature
– Basic structure:
(-COOH); (-CH3)
Fatty Acids Are Key Building Blocks
• Chain length
– Fatty acids differ in
chain length
– Lengths vary from 4
to 24 carbons
– Grouped as shortchain, mediumchain, and longchain
Fatty Acids Are Key Building Blocks
• Chain Length
– Shorter fatty acids
remain liquid at
room
temperature and
even with
refrigeration
– Shorter fatty acids
also are more
water-soluble
Fatty Acids Are Key Building Blocks
• Saturation
– Saturated fatty acids
• All single bonds between carbons
– Unsaturated fatty acids
• One or more carbon bonds is a double bond
1. Monounsaturated fatty acid (MUFA)
2. Polyunsaturated fatty acid (PUFA)
– Fats with more double bonds are generally more
liquidy
Fatty Acids Are Key Building Blocks
• Cis vs. trans
– Unsaturated fatty
acids can vary in shape
– Cis fatty acids
• Chain is bent
• Occur naturally
– Trans fatty acids
• Chain is straighter
• Produced by
hydrogenation
Trans Fat
• In health, trans fatty acids are known to raise LDL
(“bad”) cholesterol, and lower HDL (“good
cholesterol”), promote systemic inflammation, and
increase triglycerides in your blood.
• History and how it is made:
– In Europe (1910): needed a cheaper butter
substitute for soldiers
– In US (1960s): People wanted to eat a “healthier
and cheaper butter”  food scientists decided to
hydrogenate vegetable oil to solidify them
Fatty Acids are Key Building Blocks
• Nonessential and essential fatty acids
1. Nonessential fatty acids
• Can be made in the body
• Not “essential” to have in your diet
Fatty Acids Are Key Building Blocks
• Essential and Nonessential Fatty Acids
– Essential fatty acids
• Must come from food
• Cannot be made by the body
• Two families:
–Omega-3 (alpha-linolenic acid)
–Omega-6 (linoleic acid)
• Pre-cursors to eicosanoids
Triglycerides
• Structure
– Glycerol + 3 fatty
acids
– Most fatty acids
exist as part of
triglyceride
molecules
Triglycerides
• Functions
1. Energy source: 9 kcal/g
2. Energy reserve: form of stored energy in adipose
tissue
3. Insulation and protection:
1. Visceral fat
2. Subcutaneous fat
4. Carrier of fat-soluble nutrients
5. Sensory qualities (flavor, odor, texture) in food
Triglycerides
• Functions
– Carrier of Fat-Soluble
Compounds
• Improves intestinal
absorption and
bioavailability during
digestion
– Sensory Qualities
• Contributes to food’s
flavor, odor, and texture
Triglycerides in Food
• Found in a variety of
fats and oils
– Classified by their
most prevalent
type
Triglycerides in Food
• Commercial processing of fats
– Reduces waste, prevents spoilage, increases
availability of calorie-rich oils
– Removes damaging free fatty acids
– Adds antioxidants to delay rancidity and
extend shelf life
Triglycerides in Food
• Commercial processing of fats
– Negatives
• Removes potentially healthful
phospholipids, plant sterols, and other
phytochemicals
• Further processing into solid fats increases
the proportion of trans fatty acids
Phospholipids
• Structure
– Glycerol + two fatty acids +
phosphate group
– Compatible with both fat
and water
Phospholipids
• Functions
– Ideal emulsifiers
• Keep fat suspended in water
• Keep oil and water mixed
– Perfect structural element for cell membranes
• Able to communicate with watery
environments of blood and cell fluids
• Allows other lipids to enter and exit cells
Phospholipids
• Cell membranes
– Double layer of phospholipids
– Selectively allow both fatty and water-soluble
substances into the cell
– Store fatty acids temporarily
– Plays an important role in nerve cells
Phospholipids
• Lipid Transport
– In the stomach
• Break fats into tiny particles for digestion
– In the intestine
• Continue emulsifying fat
– In the blood
• Coat the surface of the lipoproteins that
carry lipid particles to their destinations in
the body
Phospholipids
• Emulsifiers (lecithin)
– Lecithin used as an
emulsifier to combine
two ingredients that
don’t ordinarily mix,
such as oil and water
– Allows ingredients in
salad dressing to mix
well and remain mixed,
for example
Phospholipids in Food
• Occur naturally in plants and animals, but in
much smaller amounts than triglycerides
• Abundant in egg yolks, liver, soybeans, peanuts
• Not a dietary essential
Sterols
• Have a multiple-ring structure
• Best known example is
cholesterol
• Most contain no fatty acid
Sterols
• Cholesterol Functions
– Major structural
component of all cell
membranes
– Precursor of important
substances, including
• Vitamin D
• Sterol hormones
• Bile salts
Sterols
• Cholesterol Synthesis
– Primarily made in the liver
Sterols in Food
• Found only in foods of animal origin
• Typical American consumers between 250-700
mg of cholesterol and 250 milligrams of plant
sterols per day
Lipid Digestion and Absorption
• Digestion of Triglycerides and Phospholipids
– Mouth
• Chewing and lingual lipase start digestion
– Stomach
• Breaks triglycerides down to diglycerides and
free fatty acids
– Small intestine
• Bile and pancreatic lipase emulsify and break
down the fats for absorption
• Intestinal cells absorb glycerol and fatty acids
into the bloodstream
Lipid Digestion and Absorption
• Lipid absorption
– Micelles
• Water-soluble globules with a fatty core
• Carry monoglycerides and long-chain
fatty acids to microvilli
• Bile recycling pathway known as
enterohepatic circulation
Lipid Digestion and Absorption
• Lipid absorption
– Lipoprotein
– Cylomicron
• Deliver dietary lipids from intestines to
cells and liver
Lipid Digestion and Absorption
• Digestion and absorption of sterols
– Body absorbs about 50% of dietary cholesterol
• Dietary fat increases absorption
• Plant sterols and dietary fiber decrease
absorption
Transportation of Lipids in the Body
• Lipids packaged into
lipoprotein carriers in order
to travel in the bloodstream
• Lipoproteins differ by size,
density, and the composition
of their lipid cores
Transportation of Lipids in the Body
• Chylomicrons
– Form in the intestinal
tract
– Enter the lymphatic
system
– About 90 percent fat
– Liver uses remnants as raw
material for very-lowdensity lipoproteins
Transportation of Lipids in the Body
• Very-Low-Density
Lipoproteins (VLDLs)
– Deliver
triglycerides to
cells
Transportation of Lipids in the Body
• Intermediate-Density
Lipoproteins (IDLs)
– Converted to lowdensity lipoproteins
Transportation of Lipids in the Body
• Low-Density
Lipoproteins (LDLs)
– Deliver cholesterol
to cells
Transportation of Lipids in the Body
• High-Density
Lipoproteins (HDL)
– Pick up cholesterol
for removal or
recycling
Recommendations for Fat Intake
• Recommended intake
– Reduce saturated fat, trans fat, and cholesterol
– Total fat: 20–35% of calories
– Less than 10% of calories from saturated fat
– Less than 300 mg per day of cholesterol
Recommendations for Fat Intake
• Essential fatty acid requirements
– Linoleic acid should provide about 2% of
calories
• Omega-6 and omega-3 balance
– Ratio of 6:1 omega-6 to omega-3 fatty acids
• Seafood (fatty fish), canola or soybean oil
Recommendations for Fat Intake
• Current dietary intakes
– Americans eat ~33% of total calories from fat
– Average calorie intake has increased =
Americans consuming more total grams of fat
– Saturated fat intake ~11%
• Cheese, pizza, grain-based desserts, chicken,
sausage, etc.
Recommendations for Fat Intake
• Role of fat replacers
– Different types of composition
– Olestra
• Sucrose + fatty acids
• Indigestible— provides no calories
• Reduces absorption of fat-soluble vitamins
Lipids and Health
• Heart disease
– Major risk factors
• High blood cholesterol
–High LDL and low HDL
• Smoking
• High blood pressure
Lipids and Health
• Reducing heart disease risk
– AHA diet and lifestyle recommendations
• Consume an overall healthy diet
• Aim for a healthy body weight
• Aim for a desirable lipid profile
• Aim for normal blood pressure
• Aim for normal blood glucose levels
• Be physically active
• Avoid use of and exposure to tobacco products
Lipids and Health
• Reducing heart disease risk
– AHA recommendations
• Balance calorie intake and physical activity to
achieve or maintain a healthy body weight
• Consume a diet rich in fruits and vegetables
• Choose whole-grain, high-fiber foods
• Consume fish, especially oily fish, at least twice
a week
• Limit your intake of saturated and trans fat and
cholesterol
Lipids and Health
• Reducing heart disease risk
– AHA recommendations (cont.)
• Minimize your intake of beverages and foods
with added sugars
• Choose and prepare foods with little of no salt
• If you consume alcohol, do so in moderation
• Follow the AHA recommendations when eating
outside of the home
Lipids and Health
• Obesity
– High-fat diets promote weight gain
– Significant within the U.S. population
• 34.9% of American adults
• 17% of American children and adolescents
Lipids and Health
• Metabolic syndrome
– Affects ¼ of American adults
– Cluster of at least three symptoms
• Excess abdominal fat
• High blood glucose
• High serum triglycerides
• Low HDL cholesterol
• High blood pressure
Lipids and Health
• Cancer
– Results from complex mix of lifestyle,
hereditary, and environmental factors
– Role of nutrition and diet complex
• Evidence suggests 30-40% are due to poor
food choices and physical inactivity
• Some dietary factors act as promoters, while
others serve a protective role
Lipids and Health
• Cancer
– Dietary and lifestyle factors for reducing cancer
risk
• Maintain a healthful weight
• Adopt a physically active lifestyle
• Consume a healthy diet
• Limit alcohol consumption
Lipids and Health
• Putting It All Together
– Healthy People 2020 objectives target reducing
deaths from heart disease and stroke and
reducing the number of adults with high blood
cholesterol levels