Chapter 5
The Lipids: Fats, Oils,
Phospholipids, and
Sterols
Instructor: Alia Makhlouf
Definition:
a family of compounds soluble in organic
solvents (ether, benzene…) but NOT in
water.
Functions of Fat
Fat is the chief storage form for excess energy.
Fat is stored in specialized cells called fat cells that
have the ability to enlarge almost indefinitely.
Fat serves as shock absorber around the internal
organs.
The fat blanket under the skin (adipose tissue)
serves as an insulating layer.
Fat is also part of all cell membranes.
Vitamin A, D, E,& K are only soluble and in fat-rich
foods.
Fat contributes to taste and sensory appeal of
foods.
Fat slows digestion and provides satiety.
Introducing the Lipids
Lipids in foods and the human body fall
into three classes:
1. Triglycerides
2. Phospholipids
3. Sterols
Usefulness of Fats in the Body
When we say “fat,” we generally mean
triglycerides
1-Triglycerides: Fatty Acids and Glycerol
95 percent of dietary fat and stored fat
Triglyceride
–
Glycerol + 3 fatty acids
Saturated versus Unsaturated Fatty Acids
Fats melt at different
temperatures
Saturated fats – solid at
room temperature…mainly
animal sources*
Unsaturated fats – liquids
at room temperature… mainly
vegetable sources
Chemically: Saturated versus Unsaturated Fatty
Acids
Saturated fatty acid – filled to capacity with
hydrogen atoms
Unsaturated fatty acid – missing hydrogen
– Monounsaturated – one point of unsaturation
– Polyunsaturated – two or more points of
unsaturation (PUFA)
Saturated versus Unsaturated Fatty Acids
Saturated versus Unsaturated Fatty Acids
2- Phospholipids
Phospholipid
– Glycerol + two fatty acids + phosphorus
– Phosphorus part makes it soluble in water
– Fatty acids make it soluble in fat
– Therefore can serve as an emulsifier
– Key role is in cell membranes
Digestion and Absorption of Fats
In the stomach, fat floats on the watery
fluids.
In the small intestine, bile emulsifies fat.
Digestion and Absorption of Fats
Digestion and Absorption of Fats
Emulsified fat is then digested by enzymes.
Digestive tract absorbs triglycerides from a
meal with up to 98 percent efficiency.
3- Sterols
Sterols
–
Large molecules consisting of interconnected rings
of carbon atoms with side chains of carbon,
hydrogen, and oxygen attached
–
Cholesterol
•
is found in all animal cell membranes
•
is nonessential, (made by the body)
•
forms plaques that cause atherosclerosis
How Can I Use My Stored Fat For Energy?
The body can also store excess carbohydrate as fat.
Transportation of fat in the blood as Lipoproteins:
LDL, HDL
– Low-density lipoproteins (LDL) transport
cholesterol and other lipids to the tissues.
– High-density lipoproteins (HDL), which are
critical in the process of carrying cholesterol
away from body cells to the liver for disposal.
The LDL and HDL Difference
LDL – larger, lighter, and richer in
cholesterol. Delivers cholesterol and
triglycerides from the liver to the tissues.
–
LDL – Less healthy
HDL – smaller, denser, and packaged with
more protein. HDL scavenge excess
cholesterol and phospholipids from the
tissues for disposal.
–
HDL - Healthy
The Importance of LDL and HDL Cholesterol
The more of these factors present in a person’s life,
the more urgent the need for changes in diet and
other controllable factors to reduce heart disease
risk:
• High blood LDL
• Low blood HDL
• High blood pressure
• Type 2 diabetes
• Obesity
• Physical inactivity
• Cigarette smoking
• Atherogenic diet
How many factors are in
your life?
Essential Fatty Acids
When the diet is deficient in all of the
polyunsaturated fatty acids, symptoms
include:
• Reproductive failure
• Skin abnormalities
• Kidney and liver disorders
• Growth and vision impairment in infants
The body stores EFA, so extreme
deficiencies are rare.
EFA:Omega-6 And Omega-3 Fatty Acid Families
Linoleic acid is the “parent” member of the
omega-6 fatty acid family
–
Abundant in vegetable oils
Linolenic acid is the “parent” member of the
omega-3 fatty acid family
• Linolenic acid is abundent in fish oil and flaxseed oil
Fish: Benefits and Cautions
Fish is the only good food source of omega 3
Omega-3 Fatty Acid
• are made in limited amounts in the body
• abundant in fish oils
• lower blood pressure
• prevent blood clot formation
• protect against irregular heartbeats
• may reduce inflammation
• essential for normal infant growth and
development
• may support immune system
• may inhibit cancers
Eat Fish For Fish Oil
Cardiovascular deaths
occur less frequently
in countries with
higher intakes of EPA
and DHA from
seafood.
What About Fish Oil Supplements?
Fish oil supplements are not recommended
because:
• they may raise LDL
• high intakes may increase bleeding times
• high intakes may interfere with wound
healing
• high intakes may suppress immune function
• high intakes may upset the proper balance
between omega-3 and omega-6 fatty acids
• they may contain toxins
• long-term effects are unknown
What Is “Hydrogenated Vegetable Oil,”?
Vegetable oils become more saturated when
they are hydrogenated.
Points of unsaturation are vulnerable to
attack by oxygen (oxidation).
When the unsaturated points in the oils of
food are oxidized, the oils become rancid.
Hydrogenation forces hydrogen into the
liquid oil, making the oil more saturated as
it accepts the hydrogens.
What Is “Hydrogenated Vegetable Oil,” And What’s It
Doing in My Chocolate Chip Cookies?
Why," Hydrogenated Vegetable Oil,”?
Hydrogenated fats:
• Resist rancidity; more resistant to oxidation
• Are firmer textured; more spreadable
• Have a higher smoking point than
unsaturated oils
• Are unhealthy
What Is “Hydrogenated Vegetable Oil,” And What’s It
Doing in My Chocolate Chip Cookies?
Baked goods often contain hydrogenated fats
Formation of Trans Fatty Acids
Trans fatty acids occur in small amounts in
nature, mostly in dairy products
A lot of trans fatty acids formed during
hydrogenation and frying of oils
Health Effects of Trans Fatty Acids
Consuming trans fat poses a risk to heart
and arteries by:
– Raising blood LDL cholesterol
– Lowering blood HDL cholesterol
– Increasing tissue inflammation, a key player in
heart disease
– Replacing heart-healthy oils
Dietary Fat, Cholesterol, and Health
A diet too high in saturated or trans fats
invites heart and artery disease.
Some studies suggest a high saturated fat
diet that is also low in fish oils may increase
the risk of certain cancers.
Obesity is more likely since fat has 9
calories per gram.
What Does Food Cholesterol Have to Do With Blood
Cholesterol?
Saturated food fats (and trans fat) raise
blood cholesterol more than food cholesterol
does.
Dietary cholesterol makes a smaller but still
significant contribution to elevated blood
cholesterol.
Recommendations Applied
To lower LDL
– Reduce saturated fat
– Reduce trans fat
– Substitute monounsaturated or PUFA
– Eat cholesterol in moderation
Consumer Corner: Fat Replacers
Consumers wishing to reduce their intakes
of fat, saturated fat, and trans fat can
choose from thousands of products that are
lower in fat than traditional ones.
Example: Olestra
Consumer Corner: Fat Replacers
Added Fats
Fats added to foods during preparation or at the
table are a major source of fat in the diet.
Majority of fats are hidden in fried foods, baked
goods, sauces, and mixed dishes.
These fats provide about 5 grams of pure fat,
providing 45 calories
• 1 tsp oil or shortening
• 1 ½ tsp mayonnaise, butter, or margarine
• 1 tbl regular salad dressing, cream cheese, or heavy
cream
• 1 ½ tbl sour cream
Food Feature:
Defensive Dining
Other tips to revise high-fat recipes
• Grill, roast, bake, microwave, stir-fry, or poach foods
• Choose larger portions of salad greens or vegetables
and use dressings lightly
• Reduce or eliminate “add-ons” such as butter, creamy
sauces, cheese, bacon
• Cut recipe amounts of meat in half; use only lean
meats
• Use defatted soups and gravies
• Make prepared mixes, such as rice, without the fats
called for on the label
Olive Oil: The Mediterranean Connection
For those eating a Mediterranean diet rich in
olives and olive oil:
• Lowers total and LDL cholesterol and not
HDL
• Reduces LDL cholesterol’s vulnerability to
oxidation
• Reduces blood-clotting factors
• Provides phytochemicals that act as
antioxidants
• Lowers blood pressure
The Mediterranean Diet: Beyond Olive Oil
Olive oil cannot take all the credit for lower
rates of heart disease seen with the
Mediterranean diet.
Other important factors are:
• Lower intakes of red meats
• Higher intakes of nuts, vegetables, and fruits
• Higher intake of fish and seafood
The Mediterranean Diet: Beyond Olive Oil
Olives and their oil may benefit heart health
Nuts: More Than A High-Calorie Snack Food
Nuts provide up to 80 percent of their
calories from fat and one ounce has over
200 calories
But, nuts are linked to heart health!!
Nuts may lower heart disease because they
are:
• Low in saturated fats
• High in fiber, vegetable protein, and vitamin
E
• High in phytochemicals that act as
antioxidants
Nuts: More Than A High-Calorie Snack Food
Stay mindful of calories when snacking on nuts
Conclusion
Adopting some traditional Mediterranean eating
habits may serve the needs of those who enjoy
somewhat more fat in the diet.
In addition to following the Mediterranean plan:
–
Reduce fats from convenience foods and fast foods
–
Choose small portions of meats, nuts, and poultry
–
Watch calories
–
Be physically active