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The Lipids
Fats, Oils,
Phospholipids, and
Sterols
Learning Objec9ves
• A
– Describe the structure of a triglyceride no9ng the differences
between saturated and unsaturated fats
– Summarize the processes of lipid diges9on, absorp9on,
transport and u9liza9on in the body, including the significance of
the lipoproteins
– Explain why manufacturers frequently hydrogenate fats and
possible health implica9ons of consuming the trans-‐faJy acids
formed during hydrogena9on
– Plan a diet containing fat in the right kinds and amounts to
provide op9mal health, while addressing the issue of pleasure in
ea9ng
Introduc9on
• Lipids
– A family of organic compounds soluble in organic
solvents but not in water
– Include triglycerides (fats and oils), phospholipids,
and sterols
Introduc9on
• Cholesterol
– A member of the group of lipids known as sterols
– A so< waxy substance made in the body for a
variety of purposes
– Also found in animal-‐derived foods
Introduc9on
• Fats
– Lipids that are solid at room temperature
Introduc9on
• Cardiovascular disease (CVD)
– Disease of the heart and blood vessels
– Disease of the arteries of the heart is called
coronary heart disease (CHD)
Introducing the Lipids
• Lipids in foods and in the human body fall into
three classes
– Triglycerides
• ≈95% of all lipids in foods and the human body
– Phospholipids
• For example, lecithin
– Sterols
• For example, cholesterol
Usefulness of Fats
in the Body
• When people speak of fat, they are usually
talking about triglycerides
– The term fat will be used in the following
discussion
Usefulness of Fats
in the Body
• Fat
– Body’s chief storage form for the energy from
food eaten in excess of need
• Valuable survival mechanism for people who live a
feast-‐or-‐famine existence
– Provide most of the energy needed to perform
much of the body’s work
• Especially muscular work
Usefulness of Fats
in the Body
• Most body cells can store only limited fat
– Some cells are specialized for fat storage
• These fat cells seem to expand indefinitely
– The more fat they store, the larger they grow
• Adipose (fat) 9ssue secretes hormones and produces
enzymes that influence food intake and affect the
body’s use of nutrients
Usefulness of Fats
in the Body
• Glucose, in the form of glycogen, is not the
body’s major form of energy storage
– Glycogen stores a large amount of water
• Therefore it is heavy and bulky
• Thus, the body cannot store enough to provide energy
for very long
Usefulness of Fats
in the Body
• Fat is the body’s major storage form of energy
– Fats pack 9ghtly together without water
• Rela9ve to carbohydrate, much more fat can be stored
in a small space
– Gram for gram, fats provide more than 2x the
energy of carbohydrate
• Making fat an efficient storage form of energy
Usefulness of Fats
in the Body
• Body fat
– The amount on a normal-‐weight person is more
than sufficient to provide energy for an en9re
marathon or to baJle disease should the person
become ill and stop ea9ng for a while
Usefulness of
Fats
in the Body
• Other func9ons of fat
– Shock absorbers
• Pads of fat surround vital internal organs
– Thermoregula9on
• Fat pads under the skin insulate the body from extremes
of temperature
– Cell membranes
• Lipids are a component of cell membranes
Usefulness of Fats
in the Body
• Essen9al nutrients
– The fat-‐soluble vitamins (A, D, E, and K) are
soluble in fat
• Found mainly in foods that contain fat
– Absorbed more efficiently from these foods
– Fat also aids in the absorp9on of some phytochemicals
– Essen
• Serve as raw materials from which the body makes
certain required molecules
Usefulness of
Fats in Food
• The energy density of fats makes food rich in
fat valuable in many situa9ons
– For example, a hunter or hiker needs to consume
a large amount of food energy to travel long
distances or to survive in intensely cold weather
• For a person who is not expending much energy in
physical work, the same high-‐fat foods may deliver
many unneeded calories in only a few bites
Usefulness of
Fats in Food
• People naturally like high-‐fat foods
– As fat becomes less expensive and more available
in a given food supply, people seem to choose
diets providing greatly increased amounts of fat
– Fats carry many dissolved compounds that give
foods en9cing aroma and flavors
– Fat also lends a tenderness to foods such as meats
and baked goods
Usefulness of
Fats in Food
• Fat contributes to sa
experience a
physiological events that slow the emptying of the
stomach and promote sa9ety
• Even before the sensa9on of fullness stops them
people can easily overeat fat-‐rich foods because of the
delicious taste
A Close Look at Lipids
• Each class of lipids possess unique
characteris9cs
Triglycerides:
FaJy Acids and Glycerol
• Triglyceride = 3 fa>y acids + glycerol
– FaJy acids
• Organic acids composed of carbon chains of various
lengths
– Each has an acid end and hydrogens aJached to all of the
carbon atoms of the chain
– Differ on the basis of length and degree of satura9on
– Glycerol
• An organic compound, three carbons long
• Serves as the backbone for triglycerides
Triglycerides:
FaJy Acids and Glycerol
• Triglycerides usually include a mixture of faJy
acids
– The nature of the faJy acids determines if the
triglyceride is hard or so<
– Mostly shorter-‐chain faJy acids or unsaturated
ones are so
Triglycerides:
FaJy Acids and Glycerol
• Each species of animal makes its own
characteris9c kinds of triglycerides
– A func9on governed by gene9cs
Triglycerides:
FaJy Acids and Glycerol
• Fats in the diet
– Can affect the types of triglycerides made
• Dietary fats are o
– For example, many animals raised for food can be fed diets
containing so
Saturated versus Unsaturated FaJy
Acids
• Satura9on refers to whether or not a faJy
acid chain is holding all of the hydrogen atoms
it can hold
– Point of satura
addi9onal hydrogen atoms can easily be aJached
Saturated versus Unsaturated FaJy
Acids
• Saturated fa>y acid
– Every available bond from the carbons is holding a
hydrogen
• Monounsaturated fa>y acid
– Contains one point of unsatura9on
• Polyunsaturated fa>y acid (PUFA)
– Contains two or more points of unsatura9on
Saturated versus Unsaturated FaJy
Acids
• Degree of satura9on
– Affects the temperature at which
the fat melts
• In general, the more unsaturated
the faJy acids, the more liquid the
fat is at room temperature
• In general, the more saturated the
faJy acids, the firmer the fat is at
room temperature
Saturated versus Unsaturated FaJy
Acids
• If a health-‐care provider recommends limi9ng
saturated fats or trans fats and using
monounsaturated fats or polyunsaturated fats
instead, you can generally judge by the
hardness of the fats which one to use
– Trans fats
• Contain unusual faJy acids that are formed during
processing
Saturated versus Unsaturated FaJy
Acids
• To determine if an oil you use contains
saturated fats
– Place the oil in the refrigerator and watch for
cloudiness
– The least saturated oils remain the clearest
Saturated versus Unsaturated FaJy
Acids
• Most vegetable and fish oils are rich in
polyunsaturates
– Some vegetable oils (especially olive and canola
oil) are rich in monounsaturates
– But beware
• Some nondairy whipped dessert toppings use coconut
oil in place of cream (buJerfat)
– The faJy acids of coconut oil are more saturated than those
of cream and seem to contribute to heart disease risk
– As do trans fats
– Palm oil ?
Saturated versus Unsaturated FaJy
Acids
• Animal fats are generally the most saturated
• There is a benefit to heart health when
monounsaturated or polyunsaturated fats
replace saturated and trans fat in the diet
Saturated versus Unsaturated FaJy
Acids
• Olive oil
– Rich in monounsaturated faJy acids
– Evidence from Mediterranean regions suggests
that olive oil confers a degree of protec9on
against heart disease when it is used in place of
other fats
– Dark-‐colored olive oils also deliver valuable
phytochemicals
Saturated versus Unsaturated FaJy
Acids
• Canola oil
– Rich in both monounsaturated and
polyunsaturated faJy acids
– Supports heart health when replacing saturated
fats in the diet
Phospholipids and Sterols
• Phospholipids = 2 faJy acids + glycerol + a
phosphorus-‐containing molecule
– FaJy acid is soluble in fat
– Phosphorus is soluble in water
• Phospholipids are emulsifiers
– A substance that mixes with both fat and water
and permanently disperses the fat in the water
• Forming an emulsion
Phospholipids and Sterols
• Food processors blend fat with watery
ingredients by way of emulsifica
an emulsifier
– In salad dressings vinegar and oil separate to form
two layers; whereas mayonnaise, also made of
vinegar and oil, never forms two separate layers
• The difference is the presence of lecithin, an emulsifier,
in mayonnaise
Phospholipids and Sterols
• Lecithin and other phospholipids play key
roles in the structure of cell membranes
– Phospholipids are able to help fats travel back and
forth across the lipid-‐containing membranes of
cells into the watery fluids on both sides
– Lecithin supplements have no special ability to
promote health
• The body can make all that it needs
Phospholipids and Sterols
• Sterols
– Large, complicated molecules consis9ng of
interconnected rings of carbon atoms with side
chains of carbon, hydrogen, and oxygen
Phospholipids and Sterols
• The sterol cholesterol serves as the precursor
for making bile
– An emulsifier made in the liver and stored in the
gallbladder
• Does not digest fats
• Emulsifies fats in such a way that enzymes in the
watery fluids may contact it and split the faJy acids
from their glycerol for absorp9on
• Vitamin D and sex hormones are also sterols
Phospholipids and Sterols
• Cholesterol
– Component of cell membranes
– Can be made by the body
• Not an essen9al nutrient
– Forms the major parts of the plaques that narrow
arteries in atherosclerosis
• The underlying cause of heart aJacks and strokes
Lipids in the Body
• Lipids affect the body’s func9oning and
condi9on
• Demand special handling because fat
separates from water, and body fluids consist
largely of water
Diges9on and
Absorp9on of Fats
• Tongue
– An enzyme produced by the tongue plays a major
role in diges9ng milk in infants
– LiJle importance to diges9on in adults
Diges9on and
Absorp9on of Fats
• Stomach
– Fat separates from the watery components and
floats as a layer on the top
Diges9on and
Absorp9on of Fats
• Small intes9ne
– Bile
• Produced by the liver
• Stored in the gallbladder
• Secreted in the small intes9ne
• Emulsifies fat
Diges9on and
Absorp9on of Fats
• No gallbladder?
– Gallbladder is just a storage organ
– Liver s9ll produces bile
• Delivers it con9nuously to the small intes9ne
– Those who have had their gallbladder removed
must reduce their fat intakes
• They can no longer store bile and release it at meal9me
– So they can handle only a liJle fat at a 9me
Diges9on and
Absorp9on of Fats
• Small intes9ne
– Emulsified fat par9cles acted on by fat-‐diges9ng
enzymes contributed by the pancreas
• Fats are split into smaller par9cles for absorp9on
• Triglycerides -‐ split faJy acids from glycerol
Diges9on and
Absorp9on of Fats
– Free faJy acids, glycerol and monoglycerides cling
together in balls surrounded by bile
• In order to be absorbed, fats must pass through the
watery layer of mucus that coats the absorp9ve lining of
the diges9ve tract
• Bile shuJles the lipids across the mucus layer to the
absorp9ve cells of the intes9nal villi
– The cells extract he lipids
– The bile may be absorbed and reused or exit with the feces
Diges9on and
Absorp9on of Fats
– The diges9ve tract absorbs triglycerides from a meal
with up to 98% efficiency
• i
...
liJle fat is excreted by a healthy system
– The process of fat diges9on takes 9me
• The more fat taken with a meal, the slower the diges9ve
system becomes
Transport of Fats
• Shorter products of lipid diges9on
– Glycerol and short-‐chain faJy acids pass directly
though the cells of the intes9nal lining into the
bloodstream
– Travel unassisted to the liver
Transport of Fats
• Larger products of lipid diges9on
– Without a mechanism to keep it dispersed, large
lipid globules would separate out of the watery
blood and disrupt the blood’s normal func9on
– Lipoproteins
• Clusters of lipids associated with protein
• Serve as transport vehicles for lipids in blood and
lymph
• Major classes include: chylomicrons, VLDLs, LDLs, and
HDLs
Transport of Fats
• Monoglycerides and long-‐chain faJy acids are
formed into lipoproteins before being
released into the lymph that leads to the
blood
– Inside intes9nal cells, they are reformed into
triglycerides and clustered together with proteins
and phospholipids
• Forming chylomicrons
– A type of lipoprotein
How Can I Use My
Stored Fat for Energy?
• Chylomicrons transport triglycerides to the fat
depots
– Muscles
– Breasts
– Insula9ng fat layer under the skin
– Etc