Transcript Document

Chapter 5: Fats, Oils and Other Lipids
Presentation created by Jill Goode Englett, University of Alabama and
Ellen Brennan, San Antonio College
Lipids

Organic compounds which do not dissolve in water but do
dissolve in fat solvents

Classes of lipids
• Triglycerides
• Sterols
• Phospholipids
© 2010 Pearson Education, Inc.
Lipids

Basic functions in the body
• Fats
- Store and provide energy (9 kcal per gram)
- Provide insulation
- Provide structure
• Cholesterol
- Cell membrane structure
- Used to make steroid hormones, bile, and provitamin
D
• Phospholipids
- Help transport fat-soluble nutrients in the blood
- Cell membrane structure
© 2010 Pearson Education, Inc.
Fatty Acids


Building blocks for triglycerides and phospholipids
A chain of carbon and hydrogen atoms with a carboxyl
group at the alpha end and a methyl group at the omega end
© 2010 Pearson Education, Inc.
Figure 5.1
Fatty Acids

Higher ratio of carbon and hydrogen to oxygen than in
carbohydrates and protein

20 different fatty acids with varied length, saturation, and
shape

Different structures impart different characteristics
© 2010 Pearson Education, Inc.
Fatty Acids Vary in Length

Short-chain fatty acids
• Two to four carbons
• Liquid at room temperature

Medium-chain fatty acids
• Six to ten carbons

Long-chain fatty acids
• 12 or more carbons
• Most common type of fatty acid in foods
© 2010 Pearson Education, Inc.
Fatty Acids Vary in Degree of Saturation

Saturated fatty acids
• All the carbons on the fatty acid are bound to hydrogen
• Usually more solid at room temperature
• Higher melting point
• More stable
© 2010 Pearson Education, Inc.
Fatty Acids Vary in Saturation

Unsaturated fatty acids
• Some carbons form a double bond with each other
instead of binding to hydrogen
• Monounsaturated fatty acid (MUFA)
- Has one carbon to carbon (C=C) double bond
• Polyunsaturated fatty acid (PUFA)
- Has two or more carbon to carbon (C=C)double bonds
• More liquid at room temperature
• Lower melting point
• Less stable
© 2010 Pearson Education, Inc.
Saturated and Monounsaturated Fatty
Acids
© 2010 Pearson Education, Inc.
Saturated and Unsaturated Fatty Acids
Help Shape Foods
Figure 5.3
Fatty Acids Differ in Double-Bond Location

The location of the first double bond in unsaturated fatty
acids affects the naming and characteristics of the
unsaturated fatty acids

Omega-3 fatty acid
• First double bond is between the third and fourth carbon
from the omega end
• Example: alpha-linolenic acid (ALA)
- One of the two essential fatty acids
© 2010 Pearson Education, Inc.
The Essential Fatty Acids: Omega-3 and
Omega-6
Figure 5.4
Fatty Acids Differ in Double-Bond Location

Omega-6 fatty acid
• First double bond is between the sixth and seventh
carbon from the omega end
• Example: linoleic acid
- One of the two essential fatty acids
© 2010 Pearson Education, Inc.
Unsaturated Fatty Acids Vary in Shape

Unsaturated fatty acids form two different shapes
© 2010 Pearson Education, Inc.
Figure 5.5
Fatty Acids and Rancidity

Rancidity: spoiling of fats through oxidation
• The more double bonds there are, the more susceptible to
oxidation and rancidity
PUFA > MUFA > Saturated fatty acids

Ways to enhance stability of fatty acids and reduce
rancidity
• Adding antioxidants
• Limiting food exposure to oxygen, heat, and light
• Hydrogenation (partial or full)
© 2010 Pearson Education, Inc.
Hydrogenation
Adding Hydrogen to an unsaturated fatty acid
Hydrogenation: Benefits and Risks

Benefits of hydrogenation
• Makes food fats more stable, increasing shelf life
• Changes the texture of the fat
- Oils become more spreadable
- Changes the characteristics of baked goods

Risks of hydrogenation
• Increases amount of trans fatty acids in foods with
partially hydrogenated oils
- Increases liver production of LDLs
- Decreases liver production of HDLs
© 2010 Pearson Education, Inc.
Trans Fatty Acids Formed During Partial
Hydrogenation
© 2010 Pearson Education, Inc.
Quick Review

Fatty acids
• Carbon and hydrogen chain, carboxylic acid, methyl group
• Basic structural units of triglycerides and phospholipids
• Differ in chain length, degree of saturation, shape
- Saturated fatty acids: no carbon to carbon double bonds
- Monounsaturated fatty acids: one C=C double bond
- Polyunsaturated fatty acids: two or more C=C double bonds
• Essential fatty acids
- Linoleic
- Alpha-linolenic acid
• Food manufactures hydrogenate or add antioxidants to unsaturated
fatty acids to reduce susceptibility to rancidity
© 2010 Pearson Education, Inc.
Triglycerides

Three fatty acids connected to a glycerol backbone
© 2010 Pearson Education, Inc.
Portion of Figure 5.7
Triglycerides

Most common lipid both in foods and in the body

Make up about 95% of lipids found in foods

Functions
• Add texture
• Add flavor to foods
• Make meats tender
• Energy storage in adipose tissue
© 2010 Pearson Education, Inc.
Caution:
High levels in
the blood are
a risk factor
for heart
disease
Phospholipids



Hydrophilic on one end; hydrophobic on the other
Make up the phospholipid bilayer in the cell membrane
• Lecithin (a.k.a. phosphatidylcholine)
- A major phospholipid in the cell membrane
- Used as an emulsifier in foods
Synthesized by the liver
© 2010 Pearson Education, Inc.
Portion of Figure 5.8
Phospholipids’ Role in Cell Membranes
Figure 5.9
Sterols




More complex than phospholipids or triglycerides
• Four connecting rings of carbon and hydrogen
Do not provide energy
Cholesterol is the best known sterol; Not essential in diet
• Part of cell membrane structure
• Used to make bile, steroid hormones, provitamin D
Phytosterols – major plant sterols
© 2010 Pearson Education, Inc.
Figure 5.11
Quick Review
© 2010 Pearson Education, Inc.
Figure 5.12
Fats in Food
| Fats in Food
Quick Review



Triglycerides
• Found in the body
• Stored in the adipose tissue
• Major source of energy
Phospholipids
• An important part of cell membrane structure
• Lecithin
- Part of cell membrane
- Used as an emulsifier in some foods
Sterols
• Do not contain fatty acids
• Do not provide energy
© 2010 Pearson Education, Inc.
What Happens to the Lipids You Eat?

Lipids from foods
• Fat, phospholipids, and sterols

Emulsified by bile

Fats are digested by lipase into
• Free fatty acids, glycerol, and monoglycerides
© 2010 Pearson Education, Inc.
Figure 5.13
Figure 5.13
Figure 5.13
Figure 5.13
Most Fat Is Digested and Absorbed in the
Small Intestine

Fat tends to cluster in the chyme

Fat stimulates the secretion of cholecystokinin (CCK) from
the duodenum

CCK stimulates the gallbladder to release bile and the
pancreas to release pancreatic lipase

Bile emulsifies fat, increasing the surface area of the fat
droplets

The triglycerides in the smaller fat droplets can then be
digested by pancreatic lipase
© 2010 Pearson Education, Inc.
Handling of Sterols and Phospholipids in the
Small Intestine

Sterols
• Not digested
• Absorbed intact through intestinal membrane
• Those which bind with fiber are not absorbed in small
intestine and are excreted in the feces

Phospholipids
• Digested by phospholipases
© 2010 Pearson Education, Inc.
Lipid Absorption

Short- and medium-chain fatty acids can be absorbed
directly into the portal circulation

Glycerol and long-chain fatty acids are absorbed from
micelles in the intestinal lumen into the intestinal lining
cells

Once in the intestinal lining cells
- Triglycerides are reformed
- The triglycerides combine with phospholipids,
cholesterol and protein to form chylomicrons
© 2010 Pearson Education, Inc.
Chylomicrons Facilitate Lipid Absorption

Chylomicrons are too large
to be absorbed directly into
the bloodstream
• Absorbed via the lacteal
and into the lymph
• Lymph later enters blood
stream through thoracic
duct near the heart
© 2010 Pearson Education, Inc.
Figure 5.15
Absorption of Dietary Lipids
Figure 5.16
Serum Lipoproteins Transport Lipids
Through the Blood

Serum lipoproteins are composed of differing amounts of
fat (TG), cholesterol, phospholipid (PL), and protein
• Chylomicrons – mostly dietary fat
• Very low-density lipoproteins (VLDLs) – mostly fat
made by the liver
• Low-density lipoproteins (LDLs) – mostly cholesterol
• High-density lipoproteins (HDLs) – mostly protein
© 2010 Pearson Education, Inc.
The Ratio of Protein to Lipid Determines the
Density of the Lipoprotein
Figure 5.17
Serum Lipoproteins Transport Lipids
Through the Blood

Very low-density lipoproteins (VLDLs) are made in the
liver and they are mostly triglyceride

As the VLDLs deliver triglycerides to the adipose tissue
and other cells, they shrink in size and become LDLs

LDLs are mostly cholesterol and are sometimes called
“bad” cholesterol because they can contribute to plaque
formation in arteries. Liver should remove these from the
blood.

HDLs are made by the liver and are sometimes “good”
cholesterol because they can remove deposited cholesterol
from plaque
© 2010 Pearson Education, Inc.
The Roles of VLDL, LDL, and HDL Lipoproteins
Figure 5.18
Lipoproteins
| Lipoproteins
Quick Review




Most fats are digested in the small intestine with the help of
bile acids and pancreatic lipase
Short- and medium-chain fatty acids are absorbed directly
into the bloodstream
Longer chain fatty acids and other remnants of fat digestion
• Packaged in chylomicron lipoprotein carriers
• Travel in lymph before entering the bloodstream
Lipoproteins are globular shaped transport carriers
• Outer shell high in protein and phospholipids
• Inner core carries insoluble fat, cholesterol, and other
lipids through lymph and bloodstream
© 2010 Pearson Education, Inc.
Quick Review




VLDLs and HDLs are synthesized in the liver
VLDLs eventually become LDLs after depositing some
fatty acids in the body’s cells
LDLs deposit cholesterol in the cells and arterial walls
HDLs remove cholesterol from the arteries and deliver it to
the liver to be used in the synthesis of bile or excreted in
the feces
© 2010 Pearson Education, Inc.
Functions of Fat







Source of energy
Preferred storage form of energy in animal body
Form body structures
Regulate metabolism (eicosanoids)
Enhance absorption of fat-soluble vitamins
Provide insulation to help regulate body temperature
Cushion major organs
© 2010 Pearson Education, Inc.
Fat Is Used as Energy

Fat
• Provides concentrated source of kilocalories
- 9 kilocalories per gram
• Readily available when the body needs energy
• Body’s main source of energy throughout the day
• Stored in adipose tissue (subcutaneous, intra-abdominal,
layered through muscles)
© 2010 Pearson Education, Inc.
Fat Is Used as Energy

Fat
• Fat can be synthesized (lipogenesis) in both the liver and
the adipose tissue from any source of kcals
• Body has an unlimited ability to store excess energy as
fat in adipocytes
- Fat synthesized in the liver is carried to the adipose
tissue for storage on VLDLs
- Fat cells have the capacity to enlarge as much as 1,000
times their original size
- Body has the ability to produce additional fat cells
© 2010 Pearson Education, Inc.
Fat Is Used as Energy


Preferred source of energy for the heart, liver, and muscles
Fat cannot sustain life alone
• Some glucose is also needed
• Only the glycerol from the fat can be converted to
glucose
© 2010 Pearson Education, Inc.
Fat Helps Insulate and Protect


Fat in subcutaneous tissue
• Insulates body
• Maintains body temperature
Fat protects bones and vital organs from trauma
• Too much fat eliminates the protective benefit
• Too little puts the body at risk
© 2010 Pearson Education, Inc.
Role of Adipose Tissue in Fat Metabolism

Fat synthesis (lipogenesis)
• Stimulated by insulin after a meal

Fat storage
• LPL (lipoprotein lipase) breaks down TG from Chylomicrons and
VLDLs to move the glycerol and fatty acids into the cells where
TGs are resynthesized

Fat breakdown (lipolysis)
• HSL (hormone sensitive lipase) breaks down stored TG into fatty
acids and glycerol to return to the blood as energy is needed
• HSL is activated by glucagon, cortisol, thyroxine, ACTH, growth
hormone, epinephrine and norepinephrine
© 2010 Pearson Education, Inc.
Role of Lipoprotein Lipase
© 2010 Pearson Education, Inc.
Other Roles of the Adipose Tissue

Immune function

Inflammation

Endocrine
• Activates some hormones
• Makes adipokines: Peptide hormones produced by the fat
cells
- Leptin: signals brain to decrease food intake and increase
BMR. Levels increase with obesity, but brain becomes
resistant to the signal.
- Adiponectin: in normal amounts this hormone has antiinflammatory and possibly anti-diabetic functions. Levels
decrease with obesity, and high levels can cause some
autoimmune diseases
© 2010 Pearson Education, Inc.
Fat Cells (Adipoctyes):
© 2010 Pearson Education, Inc.
Essential Fatty Acids: Cell Membrane
Structure


Linoleic acid
• Essential fatty acid of the omega-6 family
• Can be elongated and converted to arachidonic acid (20C)
Alpha-linolenic acid
 Essential fatty acid of the omega-3 family
 Can be elongated and converted to
- eicosapentaenoic acid (EPA), 20C
- EPA can be elongated to docosahexaenoic acid (DHA),
22C
• Needed for healthy cell membranes
• Especially concentrated in brain, eye, and other nervous
tissue
© 2010 Pearson Education, Inc.
Essential Fatty Acids: Eicosanoids


EPA and arachidonic acid are used to manufacture
eicosanoids
Eicosanoids are hormone-like substances
• Prostaglandins, thromboxanes, and leukotrienes
• Help regulate the immune system, blood clotting,
inflammation, smooth muscle contraction, and blood
pressure
© 2010 Pearson Education, Inc.
Quick Review


Fat
• An energy-dense source of fuel
• Cushions and protects bones, organs, and nerves
• Helps maintain body temperature
• Provides essential fatty acids
• Is needed for the absorption of fat-soluble vitamins and
carotenoids
Essential fatty acids are precursors to Arachidonic acid,
EPA and DHA which manufacture
• Regulate the immune system
• Prostaglandins
• Regulate blood clotting
• Thromboxanes
• Regulate inflammation
• Leukotrienes
• Regulate blood pressure
© 2010 Pearson Education, Inc.
Quick Review

Essential functions of cholesterol
• Is part of cell membrane
• Is needed to make
- Provitamin D
- Bile acid
- Steroid hormones
© 2010 Pearson Education, Inc.
How Much Fat Do We Need Each Day?


Acceptable Macronutrient Distribution (AMDR) Range
• 20–35% of daily kilocalories from fat
For heart health
• Consume no more than 10% of total kilocalories from
saturated fat
• Limit trans fats to < 1% of total kcals
© 2010 Pearson Education, Inc.
© 2010 Pearson Education, Inc.
Best Food Sources of Fat
Sources of unsaturated fats 
© 2010 Pearson Education, Inc.
Figure 5.20
Food Sources of DHA and EPA
Figure 5.21
Facts About Fats, Oils, and Cholesterol

High intake of trans fats and saturated fats increases risk of
• Cardiovascular disease
• Stroke
• Cancer

Substituting or replacing trans fats and saturated fats with
MUFA and PUFA can lower risk
© 2010 Pearson Education, Inc.
Foods Containing Trans Fat

Hydrogenated fats are used by many commercial food
producers to
• Provide rich texture
• Increase shelf live
• Decrease rancidity

Some trans fats are naturally occurring
During the partial hydrogenation process additional trans
fats form

© 2010 Pearson Education, Inc.
Trans Fatty Acids Formed During Partial
Hydrogenation
© 2010 Pearson Education, Inc.
Major Food Sources of Trans Fat for
American Adults
Figure 5.23
Trans Fats




Trans fat may actually be worse for heart health than
saturated fats
• Raise LDL cholesterol
• Lower HDL cholesterol
FDA requires trans fat to be listed on food labels in the
Nutrition Facts panel
Must also look at the ingredient label for partially
hydrogenated fatty acids to identify if there are any trans
fatty acids in a processed food
The food industry is working to find replacements for trans
fats in foods
© 2010 Pearson Education, Inc.
Where’s the Saturated Fat in Foods?
Figure 5.22
Dietary Cholesterol Is Not Essential


The liver synthesizes cholesterol needed by the body
• Liver synthesizes ~900 mg/d
• Liver decreases synthesis based on dietary intake to
some extent
• Any extra source of calories can be converted to
cholesterol by the liver, greatest effect from
- saturated fatty acids
- trans fatty acids
To reduce the risk of cardiovascular disease, dietary
cholesterol intake should be limited to < 300 mg/day
© 2010 Pearson Education, Inc.
Food Sources of Cholesterol and Plant Sterols

Cholesterol comes from animal foods only

Phytosterols and stanols are plant sterols
• Lower LDL levels by competing with cholesterol for
absorption
• Are found in soybean oil, many fruits, vegetables,
legumes, sesame seeds, nuts, cereals, and other plant
foods
• Some food manufacturers are fortifying foods with them
to help lower cholesterol
© 2010 Pearson Education, Inc.
Which MyPlate Food Groups Contain
Fat?
© 2010 Pearson Education, Inc.
Quick Review



Dietary lipids are an important part of a healthy diet,
especially essential fatty acids
Saturated fat, trans fats, and cholesterol intake should be
limited
Dietary fat intake per day
• Should range from 20 to 35% of total kilocalories
• 5–10% of kilocalories from linoleic acid
• 0.6–1.2% of kilocalories from alpha linolenic acid
• Limit saturated fat intake to < 10% of total fat intake
• Limit trans fat intake to < 1% of total fat intake
• Limit cholesterol intake to < 300 mg
© 2010 Pearson Education, Inc.
Quick Review



Lean meat and poultry, fish, low-fat or nonfat dairy
products and limited amounts of nuts and cheese
• Best sources of essential fatty acids
• Limit intake of saturated and trans fats
Commercially prepared baked goods and snack items
• Are high in kilocalories
• Are high in saturated and trans fats
• Should be consumed rarely
Use vegetable oils in the place of butter
© 2010 Pearson Education, Inc.
Quick Review






Trans fats are made by heating oil and adding hydrogen gas
to saturate some of the carbons of the fatty acids
Trans fats raise LDL cholesterol and lower HDL
cholesterol
Trans fats are found in many commercially prepared foods
and must be listed on the food label
Other oils are being tested to replace trans fats in foods
Cholesterol is found in animal foods
Phytosterols are found in vegetable oils, nuts, legumes,
whole grains, fruits, and vegetables
© 2010 Pearson Education, Inc.
Fat Substitutes



Designed to provide the creamy properties of fat for fewer
kilocalories
Fall into three categories
• Carbohydrate-based: Majority of fat substitutes
• Protein-based: Provide a creamy texture in the mouth
• Fat-based: Give physical attributes of fat for fewer
kilocalories
Overconsumption of kilocalories from regular, low-fat, or
fat-free products can lead to weight gain
© 2010 Pearson Education, Inc.
Quick Review




Fat substitutes provide the properties of fat for fewer
kilocalories and grams of fat
Fat substitutes can be carbohydrate based, protein based, or
fat based
Some substitutes such as olestra work by passing
unabsorbed through the GI tract
Reduced-fat and fat-free foods still contain kilocalories and
should be eaten in limited amounts
© 2010 Pearson Education, Inc.
What Is Heart Disease and What Factors
Increase Risk?

Cardiovascular disease is the number-one killer of adults in
the United States
Fat and
Cholesterol
Accumulate
in the
arteries
© 2010 Pearson Education, Inc.
Arteries
narrow
Blood flow
is impeded
Decrease
oxygen and
nutrients
• Not
enough
oxygen to
the heart
• CHEST
PAIN
Atherosclerosis
Figure 5.24
Emerging risk factors
• C-reactive protein (CRP)
• Homocysteine
• Chlamydia pneumoniae
• Lp(a) protein
• Metabolic Syndrome
Quick Review







Heart disease is the leading cause of death in the United
States
It develops when atherosclerosis causes narrowing of the
coronary arteries and decreased flow of oxygen and
nutrients to the heart
Elevated LDLs are a major risk factor
Uncontrollable risk factors include age, gender, family
history, and type 1 diabetes
Controllable risk factors include type 2 diabetes, high blood
pressure, smoking, physical inactivity, excess weight, low
HDLs, elevated LDLs
HDLs can be raised by losing weight, regular exercise, and
quitting smoking
Metabolic Syndrome is a group of risk factors
© 2010 Pearson Education, Inc.
Recommended Serum Lipid Levels

Total serum cholesterol should not exceed 200mg/dl

HDL cholesterol should be 40 mg/dl or greater in men

HDL cholesterol should be 55 mg/dl or greater in women

LDL cholesterol should be below 100 mg/dl

Serum triglycerides should be below 150 mg/dl
© 2010 Pearson Education, Inc.
Lowering LDLs and Increasing HDLs




Consume less saturated and
trans fats
Avoid excessive Calorie
intake
Consume less cholesterol
Make smart, informed food
choices
• Avoid or consume
processed food in

moderation

• Eat at least two servings
of fish per week
• Consume more plant
© 2010 Pearson Education, Inc.
foods
• Consume antioxidants
and phytochemicals
• Garlic may help lower
cholesterol
• Flavonoids may help
prevent LDLs from
oxidizing
Exercise
Alcohol, in moderate
amounts, can reduce the
risk of heart disease
Healthy Fats in Foods
http://www.hsph.harvard.edu/nutritionsource/questions
/omega-3/index.html
© 2010 Pearson Education, Inc.
Lipid Information on Label
© 2010 Pearson Education, Inc.
Putting It All Together




For optimal long-term health a diet should include a proper
balance of all nutrients including fat
There are different types of lipids, some essential and
others not required from foods
Goal
• Consume mostly unsaturated fats
• Limit amount of saturated and trans fats
A plant-based diet plentiful in whole grains, fruits, and
vegetables, with some low-fat dairy and lean meats,
poultry, fish, and vegetable oil will be high in fiber and
lower in saturated fats, trans fats, and dietary cholesterol
© 2010 Pearson Education, Inc.
Any Questions?
© 2010 Pearson Education, Inc.