Transcript CHAPTER 5: LIPIDS: OILS, FATS

VISUALIZING NUTRITION
CANADIAN EDITION
Mary B. Grosvenor • Lori A. Smolin • Diana Bedoya
Chapter 5: Lipids: Oils,
Fats, Phospholipids,
and Sterols
CHAPTER 5: LIPIDS: OILS, FATS, PHOSPHOLIPIDS,
AND STEROLS
LEARNING OBJECTIVES
At the end of this chapter, you should be able to:
• Discuss benefits and risks associated with dietary fats
• Compare and contrast types of fats
• Select foods containing healthy fats and limit unhealthy
fats
THINK about this – then share within a
PAIR – then SHARE with the class
• Which foods in your diet provide fat?
• Why do you need fat in your diet?
• What are the benefits and consequences of a low-fat
diet?
Sources of dietary fats
• Animal sources: meat, cheese, dairy
• Plant sources: vegetable oils, nuts, avocados
• “Hidden” dietary fat: French fries, pizza, pasta dishes,
baked goods, salad dressings
Visible and hidden fats
The amount of fat in a food is not always obvious. The two
strips of bacon in this breakfast provide a total of 8 g of fat,
and the muffin provides 16 g.
Role of fats in food
• Provide texture, flavor, aroma to foods
• Provide energy
• Affect health positively and negatively
Canada’s changing fat intake
• According to Statistics Canada, the following changes
have been observed between 1981 and 2009:
• average fat intake has risen from 85 grams per day to 91
grams per day
• the proportion of fat in the Canadian diet has not changed
• Canadians are now eating less trans fats, less saturated fats,
and less cholesterol
© iStock[hoto.com/David Hernandez
Fat intake in Canada then and now
a. In the 1970s, a typical dinner
included high-fat meat, bread with
butter, and mashed potatoes with lots
of gravy, and it was usually served
with a glass of whole milk.
b. Today, we drink low-fat milk and
eat leaner meats, but we eat more
fat from creams, cheese, sauces,
and take-out food.
© B. o”Kane/Alamy
Fat intake in Canada then and now
c. In 1981, it is estimated that
Canadians consumed an
average of 2,214 kilocalories
and 85 grams of fat per day.
This rose to 2,358 kilocalories
and 91 grams of fat in 2009.
While our total fat consumption
has increased, since our caloric
intake has also increased, the
proportion of calories from fat in
our diet has stayed relatively
constant.
Types of lipids
• Lipids: a group of organic molecules, most of which do
not dissolve in water
• Lipids include:
• Triglycerides: made up of fatty acids and glycerol
• Fatty acids are chains of carbon atoms with an acid group at one
end of the chain
• They determine the triglyceride’s function in the body
• Phospholipids: their structure includes a phosphorus atom
• Sterols: structure composed of multiple rings
Triglycerides and fatty acids
a. A triglyceride contains glycerol and three fatty acids. The
carbon chains of the fatty acids vary in length from short-chain
fatty acids (4 to 7 carbons) to medium-chain (8 to 12 carbons)
and long-chain fatty acids (more than 12 carbons). The types of
fatty acids in triglycerides determine their texture, taste, physical
characteristics, and actions in the body.
Triglycerides and fatty acids
© Can Stock Photo Inc./ angelsimon
Oils are fats that are
liquid at room
temperature. The
properties of the fatty
acids in vegetable oil
allow it to remain a liquid.
The amounts and types of fatty
acids in the triglycerides of
chocolate allow it to remain
brittle at room temperature,
snap when bitten into, and
then melt quickly and smoothly
in your mouth.
© iStockphoto.com/peepo
Triglycerides and fatty acids
• Saturated fats: carbon atoms are bonded to as many
hydrogen atoms as possible; no carbon to carbon
double bonds
• Plentiful in animal foods, such as meat and dairy products
• Plant oils are generally low in saturated fatty acids
• Long-chain saturated fats:
• implicated in the development of cardiovascular disease
• associated with increased levels of LDL (“bad”) cholesterol in the
blood
Triglycerides and fatty acids
• Medium-chain saturated fats:
• behave differently
• may have more beneficial effects
•
•
•
•
shorter, relatively water-soluble
quickly digested and absorbed into the blood stream
bypass peripheral fat tissue
less likely to be stored as fat
Triglycerides and fatty acids
• Unsaturated fatty acids: contain one or more
carbon-carbon double bonds
• Monounsaturated fatty acids: one double bond
• Found in a variety of foods such as meat, olive oil, avocados,
and nuts
• Historically have been thought to be cardioprotective
• Believed to lower LDL cholesterol
• More research required to clear health effects
Triglycerides and fatty acids
• Polyunsaturated fatty acids: more than one double
bond
• Found mainly in plant sources
Triglycerides and fatty acids
Essential fatty acids
Fatty acid
composition of food
Essential fatty acids
• Humans are unable to synthesize fatty acids that have
double bonds in the omega-6 and omega-3 positions
• Therefore linoleic acid (LA) (omega-6) and alphalinolenic acid (ALA) (omega-3) are considered
essential fatty acids (EFAs) and must be consumed in
the diet
Essential fatty acids
• Important for the formation of membrane
phospholipids, for fertility, red blood cell structure,
metabolism, etc.
• Used to make regulatory proteins called eicosanoids
• Omega-3 eicosanoids reduce inflammation, lower blood
pressure and have other health benefits
Essential fatty acids
• Eating Well with Canada’s Food Guide recommends
eating two or more servings of fish per week as a good
source of Omega-3 fatty acids
• Other good sources of Omega-3 fatty acids: walnuts,
canola oil, ground flaxseed and many fortified foods
Essential fatty acids
© Can Stock Photo Inc./Natika
© Don Johnston/ Alamy
© PSL Images/ Alamy
Trans-fat (trans-fatty acids)
• Small amounts occur naturally in dairy products
• Created when unsaturated fatty acids are partially
converted to saturated fatty acids by the industrialized
process of hydrogenation
• Some double bonds converted from cis to trans configuration
• Decrease the rancidity and increase shelf life
• Most health endangering dietary fats
Trans fatty acids
a. The orientation of
hydrogen atoms
around the double
bond distinguishes cis
fatty acids from trans
fatty acids. Most
unsaturated fatty acids
found in nature have
double bonds in the
cis configuration.
Trans fatty acids
b. Small amounts of trans
fatty acids occur naturally,
and larger amounts are
generated by
hydrogenation. In 2007,
Health Canada called on
food manufacturers to
voluntarily reduce the
amount of trans fat in their
products to less than 5% of
total fat, which the majority
of manufacturers have now
complied with.
Concept check
What are similarities and differences between:
• saturated and unsaturated fats?
• monounsaturated and polyunsaturated fats?
• omega-3 and omega-6 fats?
• cis-fats and trans-fats?
Calculate the trans-fat
• A bag of chips has 8 servings and has a trans-fat free
label
• Each serving has 0.4 g of trans fat (label lists as 0 g of
fat)
• If you eat ½ of the bag of chips, how many grams of
trans-fat have you consumed?
Concept check
• Canadians consume too much saturated fat and too
few omega-3 fats. What dietary recommendations
could be made to help them improve their diets?
Debate the issues
• Should the government pass additional trans-fat bans?
• Should unhealthy foods such as soda and potato chips
have an additional tax?
Phospholipids
a. Like a triglyceride, a phospholipid has a backbone of glycerol,
but it contains two fatty acids rather than three. Instead of the third
fatty acid, a phospholipid has a chemical group containing
phosphorus, called a phosphate group. The fatty acids at one
end of a phospholipid molecule are hydrophobic: insoluble in
water, but soluble in fat; whereas the phosphate-containing region
at the other end is hydrophilic: soluble in water, but insoluble in
fat.
Phospholipids
b. Since dietary lipids are hydrophobic (“water-hating”), they cannot
dissolve readily in water, making them difficult to transport in waterbased environments such as the blood. Phospholipids help suspend
lipids in watery environments by acting as emulsifiers. The salad
dressing shown here does not contain an emulsifier, so it separates
into a layer of oil and vinegar and must be shaken before it is poured
on your salad. Ranch salad dressings are emulsified so that they do
not separate when left standing.
© Can Stock Photo Inc./sadakko
Phospholipids
c. Phospholipids are an important
component of cell membranes.
They form a double-layered
sheet called the lipid bilayer by
orienting the hydrophilic,
phosphate-containing “heads”
toward the aqueous (water)
environments inside and outside
the cell and the hydrophobic fatty
acid “tails” toward each other to
form the lipid centre of the
membrane. The lipid bilayer is a
critical component of the cell, as it
limits what substances can easily
move into and out of it.
Sterols
• Sterols are a type of lipids with distinct ring structures
in their chain
• Cholesterol: sterol made by the liver and consumed in
the diet
• Present in animal cell membranes and in myelin
• Used to make vitamin D and steroid hormones (e.g., estrogen,
testosterone, cortisol)
• Dietary sources: animal products
• Plant sterols can reduce human cholesterol
• One of the leading risk factors for heart disease
Cholesterol
a. The cholesterol structure
shown here illustrates the
four interconnected rings of
carbon atoms that form the
backbone structure that is
common to all sterols.
Cholesterol
b. Egg yolks and organ meats such as liver and kidney are high
in cholesterol. Lean red meats and skinless chicken are low in
total fat but still contain some cholesterol. Cholesterol is not found
in plant cell membranes, so even high-fat plant foods, such as
nuts, peanut butter, and vegetable oils, do not contain cholesterol
Concept check
1. Where are most phospholipids found in the body?
2. Why is cholesterol not a dietary essential?
3. Which is higher in cholesterol: a 15-mL spoonful of
peanut butter or an egg?
Concept check
• How are phospholipids and cholesterol similar and
different?
• What is an example of a non-essential nutrient?
Digestion and absorption of fat
• Mostly in small intestine
• Bile: acts as an emulsifier breaking down larger lipid
droplets into smaller ones making them more
accessible to lipase (lipid digesting enzyme)
• Bile is stored in the gall bladder before entering the
small intestine
Digestion and absorption of fat
• Micelles: mixture of fatty acids, partially digested
triglycerides, cholesterol and bile; facilitate lipid
absorption
• Fat soluble vitamins (A, D, E, and K) are absorbed
through the same process
Digestion and absorption of fat
• Dietary fibre binds cholesterol to keep it from being
reabsorbed into the body from the small intestine (so
more is excreted from the body)
Lipid digestion and absorption
Transporting lipids in blood
• Lipids are hydrophobic = water fearing
(Oil and water don’t mix)
• Blood is mostly water
• Lipids are transported in blood by lipoproteins;
surrounded by hydrophilic ( = water loving) molecules
Chylomicrons
• Chylomicrons transport triglycerides, cholesterol,
phospholipids and fat-soluble vitamins from the small
intestine to body cells
• Triglycerides in chylomicrons are broken down into
glycerol and fatty acids by lipoprotein lipase (in blood
vessels) to cross membranes then are reassembled
into triglycerides in cells
• Chylomicron remnants are returned to the liver
Lipoproteins (examples: LDL & HDL)
Lipoproteins consist of a core
of triglycerides and
cholesterol surrounded by a
shell of protein,
phospholipids, and
cholesterol.
Phospholipids orient with
their fat-soluble “tails” toward
the interior of the lipoprotein
and their water-soluble
“heads” toward the watery
environment outside the
lipoprotein
Very low density lipoproteins (VLDL)
• VLDL particles are made in the liver and released to
blood
• VLDL function similar to chylomicrons (transport
triglycerides which are broken down by lipoprotein
lipase)
• Remainder of VLDL particles is either returned to the liver or
made into LDL particles
Low density lipoproteins (LDL)
• LDL particles deliver cholesterol to cells
• LDL particles bind to LDL receptors on cells to help
cholesterol move from the blood into cells
• High levels of LDL in blood increase risk of heart
disease; LDL = “bad” cholesterol
High density lipoproteins (HDL)
• Reverse cholesterol transport: HDL particles
transport cholesterol from cells to the liver; HDL =
“good “ cholesterol because it lowers cholesterol
content in blood
• The liver uses cholesterol to make bile
LDL vs. HDL
• LDL particles transport cholesterol from the liver to
body cells
• Try to decrease your blood levels of LDL
(“you want your low to be low”)
• HDL particles transport cholesterol from body cells to
the liver so they can be excreted
• Try to increase your blood levels of HDL
(“you want your high to be high”)
Lipoproteins are blood transport
particles
• We do not eat LDL and HDL
• Dietary lipids (such as cholesterol and triglycerdies)
are packaged into lipoprotein particles (such as LDL
and HDL) for transport in blood
Low density lipoproteins (LDL)
Low density lipoproteins (LDL)
Improve your lipid profile
• Decrease dietary trans-fat, saturated fat, and
cholesterol
• Increase dietary polyunsaturated fats (particularly
Omega-3 fatty acids) and monounsaturated fats
• Quit smoking
• Exercise
• Increase dietary fibre
Concept check
• If a person does not have LDL receptors, what would
you expect to happen to blood levels of LDL?
• What are examples of foods you can limit and increase
to lower your LDL and raise your HDL?
Checking student learning outcomes
• What are the benefits and risks of dietary fats?
• How are fats classified? What are the similarities and
differences between types of fat?
• Which foods should be consumed and avoided to
improve health?
Concept check
Which of the following is true?
1.Cholesterol is made in the small intestine.
2.Bile is packaged into HDL particles.
3.HDL is oxidized during atherosclerosis.
4.LDL delivers cholesterol to cells.
Concept check
• What are some benefits of lipids/fats discussed so far?
Benefits of lipids/fats
• Provide texture, flavor, aroma to foods
• Phospholipids and cholesterol are structural materials
of cellular membranes and are starting materials for
other molecules
• Help absorb fat-soluble vitamins
• Insulate, cushion, lubricate
• Provide energy
Benefits of lipids/fats
• Adipose tissue (fat tissue) stores triglycerides that can
be broken down for energy production when needed
• 1 gram of fat = 9 kcal
• 1 gram or carbohydrates or proteins = 4 kcal
• Excess calories consumed as carbohydrates or
proteins can be converted to fatty acids by the liver and
also stored as triglycerides
Adipose tissue
a. Adipose tissue is an important
source of stored energy. It also
insulates the body from changes in
temperature and provides a cushion to
protect against shock. The amount and
location of adipose tissue affect our
physical appearance, specifically our
body size and shape. This tissue is
preferentially deposited in some body
areas, such as your abdominal region,
rather than other areas, such as your
thighs and shoulders. Where adipose
tissue is stored varies across both male
and female populations and is based
almost entirely on individual genetics.
Thus, a specific diet or exercise regime
cannot honestly promise results for fat
loss from one specific location over
another
Storage of excess fatty acids
b. Adipose tissue cells contain large droplets of triglyceride that push the
other cell components to the perimeter of the cell. As weight is gained, the
triglyceride droplets enlarge and, once they reach their maximum size, they
divide, forming new adipocytes, or fat cells. When weight is lost and total
body fat is lowered, fat cells can only shrink, not disappear. Once fat cells
have been added to the body, they remain, making it more difficult to
achieve the pre-fat gain state and appearance.
Conversion of fatty acids to energy
Feasting vs. fasting
When we consume too many
calories, excess energy is
stored in the form of
triglycerides. When the energy
needs of our body are
insufficient to fuel body
processes and physical
activity, triglycerides in adipose
tissue are broken down,
releasing fatty acids, which
can be used to provide energy.
Concept check
• What are benefits and dangers of limiting fat intake?
• What are the dangers of consuming too much fat?
Lipids and disease
• The amount and type of fat you eat can affect your
health
• Too little dietary fats can affect growth, sight and
impair many physiological functions
• Too much dietary fats can increase total calorie intake
and lead to weight gain
• Too much of trans fats and saturated fats can
contribute to cardiovascular disease and cancer
Atherosclerosis
• Atherosclerosis: a type of cardiovascular disease that
involves buildup of fatty material in the artery walls
(atherosclerotic plaques)
• Atherosclerotic plaques generation occurs following
blood vessel injury, inflammation and LDL cholesterol
oxidization
• Atherosclerotic plaques can narrow blood vessels and limit
blood flow so that less oxygen and fewer nutrient molecules
are delivered to tissues
Development of atherosclerosis
Development of atherosclerosis
Atherosclerosis can lead to heart attacks
and strokes
• Atherosclerotic plaques can rupture and stimulate clot
formation in blood vessels to completely block blood
flow
• In the heart, this causes heart attacks (also called
myocardial infarctions, or MIs)
• In the brain, this causes strokes (also called cerebral
vascular accidents, or CVAs)
Risk factors for atherosclerosis and
cardiovascular disease
•
•
•
•
•
•
•
•
High blood pressure (hypertension)
Obesity
Diabetes mellitus
Smoking
Blood lipids (high LDL, triglycerides; low HDL)
Diet
Sedentary lifestyle
Family history, age, gender, race
Risk factors for cardiovascular disease
Diet and heart disease risk
Diets that prevent heart disease:
• High in fibre, antioxidants and B vitamins
• Examples: fruits, vegetables, nuts, whole grains and fish
Diet and heart disease risk
• Diets that contribute to heart disease:
• High in trans fats, saturated fats and sodium
• Examples: red meat, processed meats, hydrogenated
vegetable oils
• Health Canada was the first government in the world to
implement the mandatory labeling of trans fats on
prepackaged foods
Mediterranean diet pyramid
Cardio-protective effects of the
traditional Mediterranean and Asian
diets versus modern diets
a. In the Mediterranean region, the main
source of dietary fat is olive oil, and the
typical diet is high in nuts, vegetables,
and fruits. Fish is consumed routinely
and red meat, rarely. Despite a fat
intake that is similar to that of the
Canadian diet, the incidence of heart
disease is much lower. This diet
pyramid is based on the dietary patterns
of Crete, Greece, and southern Italy
around 1960, when the rates of chronic
disease in this region were among the
lowest in the world.
Traditional Asian diet pyramid
b. In Asian countries, plant foods that
are rich in fibre and antioxidants form
the base of the diet, and animal
products are more peripheral.
Traditional Asian diets include more
fish and seafood than red meat.
Combined with small amounts of
vegetable oil, this pattern produces a
balance of omega-3 to omega-6 fatty
acids that helps prevent heart
disease.* Routine consumption of
green tea, which is high in
antioxidants, may also contribute to
the low rate of chronic disease in the
region.* This diet pyramid was inspired
by the traditional cuisines of southern
and eastern Asia.
© Can Stock Photo Inc./dimol
© Can Stock Photo Inc./ oksix
Eating to reduce the risk of heart disease
© Can Stock Photo Inc. ./ ildi
© Can Stock Photo Inc./BVDC
Eating to reduce the risk of heart disease
Cholesterol and saturated fats in foods
Dietary fat and cancer
• Cancer is a leading cause of death in Canada
• Research indicates that the risk of cancer may be
decreased by choosing diets:
• high in fruits, vegetables, antioxidants and omega-3 fatty acids
• low in trans fats (more studies needed to determine the
association between trans fats and some cancers)
Dietary fat and obesity
• Excess dietary fat intake contributes to weight gain
• However, fat content in the diet is not the sole reason
for high rate of obesity in Canada
• Weight gain occurs when energy intake exceeds
energy expenditure regardless whether extra energy
comes from fat, carbohydrate, or protein
Concept check
• What are some benefits of diets rich in fruits and
vegetables?
• What are some consequences of diets high in animal
fats?
Concept check
• Which dietary and lifestyle changes can you make to
decrease your risk of atherosclerosis and
cardiovascular disease?
Dietary lipid recommendations
• The dietary reference intake (DRIs):
• Total fat: 20%–35% of total calories
• 30–40% for ages 1–3 & 25–35% for ages 3–18
• Adequate intake for linoleic acid = 12 g per day for women
and 17 g per day for men
• Adequate intake for alpha linolenic acid = 1.1.g per day for
women and 1.6 g per day for men
• Cholesterol, saturated fat, and trans fats: keep intake to
minimum
Making wise food choices
• Canada’s Food Guide, the section “Make Each Food
Serving Count” recommends choosing lower fat
options in all food groups
• Examples: smart fat choices from meat and meat alternatives,
milk and milk alternatives groups
Making wise food choices
Canadian Food Guide recommends making
wise fat choices
Food labels
• Pay attention to the Nutrition Facts panel
• Be careful when choosing the lower-fat content food
products; some of them may have reduced nutritional
value and may have negative health implications
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