Transcript Chapter 5 The Lipids

Chapter 5
The Lipids:
Triglycerides
Phospholipids
Sterols
Objectives for Chapter 5
• Discuss synthesis, structures, classification,
function and metabolism of lipids
• Identify the dietary sources of the different
types of lipids
• Discuss the role of lipoprotein in transport
of lipids
• Describe the relationship of lipids to chronic
diseases
• List current dietary recommendations for
lipids and how to implement them.
Lipids
• Lipids are a class of nutrients that includes:
– Triglycerides (fats and oils)
– Phospholipids
– Sterols.
• Composed of carbon, hydrogen, and
oxygen.
• Lipids are hydrophobic (insoluble in water)
• Include fat soluble vitamins (ADEK)
• Provides 9 kcal per gram
Triglycerides
• TG (fats and oils)
– composed of 3
fatty acids attached to a glycerol
• Fatty acid - is a chain of carbon atoms with hydrogen
attached that has an acid group (COOH) at one end
and a methyl group (CH3) at the other end
• Glycerol is an alcohol composed of a
three carbon chain
Methyl
end
Acid
end
Fig. 5-1, p. 140
TG
Triglycerides
– Fats are lipids that are solid at room
temperature (70 degrees)
– Oils are lipids that are liquid at room
temperature (70 degrees)
– TGs are 95% of dietary fats
• Roles of TGs
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Energy reserve when stored
Insulation
Shock protection
Use carbohydrate and protein efficiently
Fatty Acids
• Fatty acids Fatty acids vary in carbon chain
lengths, degree of unsaturation, and number of
double bonds.
– Length of the carbon chain
• Long-chain fatty acids are found primarily in meat, fish,
and vegetable oils.
• Medium- and short-chain fatty acids are found in dairy
products.
– Degree of Saturation- Saturation affects the
physical characteristics of the fat and its storage
properties
• Saturated fatty acids carry the maximum possible
number of hydrogen atoms.
Saturated vs. Unsaturated
• Saturated - When most of the fatty acids
are saturated it is called a saturated fat.
Stearic acid, an 18-carbon saturated fatty acid
Saturated vs. Unsaturated
• Unsaturated – Unsaturated fatty acids are
missing at least 2 hydrogen atoms and have
at least one double bond. There are 2 types
– Monounsaturated fatty acid (MUFA)
Oleic acid, an 18-carbon monounsaturated fatty acid
Saturated vs. Unsaturated
• Polyunsaturated fatty acids (PUFA)
– lack four or more hydrogen atoms and have at
least two or more double bonds.
– Linoleic and linolenic acid - Essential Fatty
Acids (EFAs)
– When most of the fatty acids in a lipid are
polyunsaturated it is called a polyunsaturated fat.
Linoleic acid, an 18-carbon polyunsaturated fatty acid
Saturated vs. Unsaturated
– Locations of the double bonds
• Omega3 - linolenic acid - the first double
bond is located at the third carbon from the
methyl side
• Omega 6 - linoleic acid - the first double
bond is located at the sixth carbon from the
methyl side
Linoleic acid, an 18-carbon polyunsaturated fatty acid
Omega-3 and Omega-6 Fatty Acids Compared
Saturated and Unsaturated Fatty
Acids Help Shape Foods
Fatty Acids
Degree of unsaturation
• Firmness
–
–
Saturated fats - solid at room temperature. Mostly
from animal sources
Polyunsaturated fats - liquid at room temperature.
Found in vegetable oil except, cocoa butter, palm oil,
palm kernel oil, and coconut oil
• Stability
–
–
–
Saturated fat is more resistant to oxidation.
Monounsaturated fat is less susceptible to spoilage.
Polyunsaturated fat spoils most readily.
Essential Fatty Acids
Essential Fatty Acids
• Linoleic Acid - Omega-6 Family and 18
carbon
– They are PUFA,
– Can make arachidonic acid—a conditionally
essential fatty acid with 20 carbons and 4 double
bonds
– Supplied by vegetable oils and meats
Essential Fatty Acids
• Linolenic Acid and 18 Omega-3 Family
– EPA - eicosapentaenoic acid, 20 carbon, 5 double
bonds
– DHA - docosahexaenoic acid, 22 carbons and 6
double bonds
• important for eyes, brain development, and heart disease.
• Eicosanoids – omega 3 & 6
– Made from arachidonic acid and EPA
– Like hormones but have different effects on different
cells
– Include prostaglandins, thromboxanes, and leukotrienes
• Essential fatty acid deficiencies are rare in the US
but my occur in children fed low fat or fat free diet
Essential Fatty Acids
Fatty Acids
Hydrogenation –
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Hydrogen atoms are added to monounsaturated or
polyunsaturated fats
Act more like saturated fats
resistant to oxidation
Prolong shelf life
Becomes solid at room temperature
Trans-Fatty Acids vs. Cis
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–
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Naturally, most double bonds are cis, hydrogen next to
the double bonds are on the same side.
Trans, hydrogens on opposite side of the carbon.
Trans fatty acids behave like saturated fat in the body.
Cis- and Trans-Fatty Acids Compared
Major Food Sources of Trans Fat
for American Adults
Phospholipids
Phospholipids
• contain glycerol, 2 FAs and a phosphate group
with a choline.
• A well-known phospholipid is lecithin, made by the
liver
– Food sources of lecithin include eggs, liver, soybeans,
wheat germ and peanuts.
• Soluble in both water and fat
• Roles of phospholipids
– Transport lipids and FSV through Plasma
membrane
– Used as emulsifiers in food industry
Phospholipids
Sterols
• Sterols
–
–
–
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cholesterol, vit D, testorone
Multiple-ring structure.
Found in plant and animal foods
Cholesterol is found in animal foods only meat, eggs, fish, poultry and dairy products
Sterols
Sterols
• Roles of sterols
– Needed to make bile acids, sex hormones,
adrenal hormones and vitamin D
–Component of cell membranes
–Liver produces 800-1500mg of
cholesterol daily
–Cholesterol forms deposits in the
artery wall causing artherosclerosis.
Fat Digestion
•
Mouth –
– hard fat begin to melt as they reach body
temperature
– salivary glands - lingual lipase digests short
and medium chain fatty acids found in milk.
•
Stomach—
– Lingual lipase breaks down triglycerides to
produce diglycerides and fatty acids
– gastric lipase breaks down a small amount of
fat.
– Little fat digestion takes place in the stomach.
Fat Digestion
• Small Intestine –
– most of the digestion takes place in the small intestine.
– Cholecystokinin (CCK) signals gallbladder to release bile.
– Pancreatic and intestinal enzymes breaks lipids to
monoglycerides and fatty acids.
– Phospholipids are broken down as well.
– Sterols are absorbed intact as is.
– Bile is reabsorbed in the small intestine
• Colon or large intestine
– Soluble fibers traps some bile and excreting it from the
body through the large intestine.
Lipid Absorption
• Lipid Absorption
– Glycerol and short and medium-chain fatty acids
diffuse and are absorbed directly into the
bloodstream.
– Monoglycerides and long-chain fatty acids form
micelles, are absorbed, and are reformed into
new triglycerides.
– With protein they are transported by
chylomicrons
Monoglyceride
Micelle
Protein
Triglyceride
LongChylomicron chain
fatty
acids
Large lipids such as monoglycerides
and long-chain fatty acids combine with
bile, forming micelles that are
sufficiently water soluble to penetrate
the watery solution that bathes the
absorptive cells. There the lipid
contents of the micelles diffuse into the
cells.
Lipid Transport
•
Lipid transport is made possible by a group of
vehicles known as lipoproteins. There 4
lipoproteins
1. Chylomicrons
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•
•
Largest of the lipoproteins
Least dense
Get smaller as triglyceride portion is removed by the cells
2. VLDL (Very-Low-Density Lipoproteins)
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•
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Composed primarily of triglycerides
Made by the liver
Transport lipids to the tissues
Get smaller and more dense as triglyceride portion is removed
Lipid Transport
3. LDL (Low-Density Lipoproteins)
• Composed primarily of cholesterol
• Transport lipids to the tissues
4. HDL (High-Density Lipoproteins)
• Composed primarily of protein
• Transport cholesterol from the cells to the liver
Chylomicrons: One Type of
Lipoprotein
The Various Types of Lipoproteins
and Their Composition
Lipid Transport
• Health Implications
– High LDL is associated with higher risk of
heart attack and is known as “bad”
cholesterol.
– High HDL seems to have a protective effect
and is known as “good” cholesterol
Storing Fat
• Storing Fat as Fat
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Adipose tissue readily stores fat.
Provides twice the energy as carbohydrate and protein
1 lb of body fat = 3,500 cal
Lipoprotein lipase (LPL) breaks triglycerides as they pass,
directs the parts into the cells to be used for energy or storage.
• Using Fat for Energy
– Fat supplies 60% of the body’s ongoing energy needs.
– lipase inside the adipose cells hydrolyzes triglycerides when
needed for energy.
– Fasting metabolizes fat but needs carbohydrate and protein for
complete breakdown.
– Ketone bodies
Health Effects of Lipids
•
Normal blood lipid profile
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Total cholesterol  200 mg/dL
LDL cholesterol  100 mg/dL
HDL cholesterol  60 mg/dL
Triglycerides  150 mg/dL
Atherosclerosis - Cholesterol accumulates in the
arteries
saturated fats raise LDL
Trans fat increase LDL cholesterol and decrease
HDL cholesterol
Cholesterol has less effect on blood cholesterol
than saturated fat and trans fat.
Atherosclerosis
Health Effects of Lipids
• Increasing dietary MUFA & PUFA is the
most effective way to prevent heart
disease.
• omega-3 fats help to reduce risk of
heart disease and stroke
• Balance omega-6 and omega-3
intakes
• Cancer - Fat does not initiate cancer
development but may be a promoter once
cancer has developed
• Obesity- consequence of high fat diet
Recommended Intakes
of Fat
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•
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DRI and the 2005 Dietary Guidelines
recommends fat at 20-35 % of energy
intake.
FDA - 10% of energy intake from
saturated, 30% of energy intake total fat
2005 Dietary Guidelines - choose a diet
low in saturated fat and cholesterol and
moderate in total fat.
Recommended Intakes of Fats
• Recommended Intakes of Fat
– Daily Values
• 65 g fat based on 30% of 2000-kcal diet
• 20 g saturated fat based on 10% of 2000-kcal diet
• 300 mg cholesterol
– USDA Food Guide considers saturated fats
discretionary kcalories.
– Too little fat can be detrimental to health.
Recommended Intakes
of Fat
• Linoleic acid AI
–5% - 10% of energy intake
• Linolenic acid AI
–0.6 - 1.2% of energy intake
Reducing Fat In Your Diet
• Cook with olive oil
• Nibble on nuts
• Feast on fatty fish, high in omega 3
– But beware of mercury
• Limit Fatty Meats, Milk Products, and
Tropical Oils
• Limit hydrogenated foods
Reducing Fat in Your Diet
• Fat replacers
– Artificial, ingredients derived from carbohydrate, protein or
fat.
– Replace fat in foods, but no added kcalories
– Olestra is safe but it deceases absorption of fat-soluble
vitamins and may cause diarrhea.
• Limit Fatty Meats, Milk Products, and Tropical Oils
• Limit Hydrogenated Foods
• Adopt the Mediterranean diet
– Focus on whole grains, potatoes, and pasta, vegetables
and legumes, low fat cheeses, yogurt, fruits, fish and
seafood, poultry, a few eggs and little meat
Homework
Extra credit 5 points:
Go to the supermarket and compile a list of
10 foods that contain hydrogenated fat in
the ingredient list and document the
amount of trans fat listed on the nutrition
fact panel