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Transcript
LIPIDS
Learning Objectives:
• Understand lipid terminology and
classifications
• Understand the digestion and
absorption of lipids
• Learn about the function of lipids in
the diet, and how they relate to health
issues
WHAT ARE THE LIPIDS?
•
A broad range of organic compounds
that dissolve easily in organic solvents,
but range in their solubility in water
Hydrophobic – “water-fearing”
• Lipophilic – “fat-loving”
•
CLASSES of LIPIDS
SIMPLE LIPIDS
• Fatty Acids
• Triglycerides
• Waxes
COMPOUND LIPIDS
• Phospholipids
DERIVED LIPIDS
• Sterols
FATTY ACIDS
•
•
•
•
Key building blocks for lipids
Chains of carbon atoms with a carboxyl
group at one end, and a methyl group at
the other
May be “free” or attached to another
compound
Determine the characteristics of the fat
FATTY ACIDS
CHAIN LENGTH
• Short chain = less than 6 carbons
• Medium chain = 6-10 carbons
• Long chain = 12 or more carbons
• The shorter the carbon chain, the more
liquid the fatty acid is
FATTY ACIDS
SATURATION
• SATURATED FATTY ACID =If all the
carbon atoms in the chain are joined
with single bonds, and the remaining
bonds are attached to hydrogen
FATTY ACIDS
SATURATION
• UNSATURATED FATTY ACID = If
adjoining carbons are joined by double
bonds
FATTY ACIDS
UNSATURATED
• One double bond = monounsaturated fatty
acid
• Two or more double bonds = polyunsaturated fatty acid
FATTY ACIDS
•
•
•
•
Long-chain saturated fatty acids stack
tightly and form solids at room
temperature
Monounsaturated and polyunsaturated
fatty acids don’t stack compactly and are
liquid at room temperature
Short-chain saturated fatty acids are also
liquid at room temperature
Figure 5.6
FATTY ACIDS
TWO TYPES OF BOND FORMATION:
• CIS - hydrogens on the carbons joined by
a double bond are on the same side = the
carbon chain is bent
• TRANS – hydrogens on the carbons
joined by a double bond are on the
opposite side = the carbon chain is
straighter
FATTY ACIDS
•
•
•
•
Omega-3 Fatty Acid – double bond at
carbon 3
Omega-6 Fatty Acid – double bond at
carbon 6
Omega-9 Fatty Acid – double bond at
carbon 9
*count carbons from the methyl (omega)
end

Omega 3

Omega 6

Omega 9
FATTY ACIDS
NOMENCLATURE
• Alpha and Omega
• 18:0, 18:1, etc.
FATTY ACIDS
•
•
•
Nonessential Fatty Acids – our body can
make certain fatty acids so they are not
required in the diet
Essential Fatty Acids – our bodies
cannot make C-C double bonds before
the 9th carbon from the methyl end, so
we must get these fatty acids from our
diet
EFAS = omega-6 linoleic acid & omega3 alpha-linolenic acid
FATTY ACIDS
•
Omega-3: Alpha-Linolenic Acid (ALA),
Eicosapentaenoic Acid (EPA),
Docosahexaenoic Acid (DHA)
•
Omega-6: Linoleic Acid, Arachidonic
Acid
Sources of Omega-3
Fatty Acids
•
Flaxseed, soybean oil, walnuts,
some leafy dark green
vegetables (ALA)
• Fatty fish: salmon, tuna, and
mackerel, fish oils (EPA and
DHA)
Sources of Omega-6
Fatty Acids
•
Seeds, nuts, common
vegetable oils: corn, safflower,
cottonseed, sunflower seed,
peanut (linoleic acid)
• Meat (arachidonic acid)
FATTY ACIDS
EICOSANOIDS
• A small percentage of fatty acids
become eicosanoids
• They contain 20 or more carbons
and are important in the
inflammatory process, blood vessel
dilation and constriction, and blood
clotting
EICOSANOIDS
Omega-6s
• Linoleic acid is converted to
arachidonic acid and
eicosanoids are formed.
• Overall effect: constricting blood
vessels, promoting
inflammation and blood clotting
EICOSANOIDS
Omega-3s
• Alpha-linolenic acid is converted to
eicosapentanoic acid (EPA) and
docosahexanoic acid (DHA) and
eicosanoids are formed
• Overall effect: dilating blood
vessels, discouraging blood
clotting, and reducing inflammation
TRIGLYCERIDES
STRUCTURE
• Triglyceride - three fatty acids
attached to a glycerol backbone
• Diglyceride – two fatty acids +glycerol
• Monoglyceride – one fatty acid
+glycerol
Fatty Acids
Triglyceride
TRIGLYCERIDES
FUNCTIONS
• Major lipid in the body and diet
• Stored fat provides about 60% of the
body’s resting energy needs –
compactly!
• Insulation and protection
• Carrier of fat-soluble compounds
• Sensory qualities – flavor and texture
Compound Lipids:
PHOSPHOLIPIDS
•
•
•
Contain a glycerol bonded to two fatty
acids
The phosphate group is hydrophilic while
the fatty acids groups are lipophilic
Because of this structure, phospholipids
are ideal emulsifiers, and the perfect
structure for cell membranes
Functions
Cell Membranes
• Phosholipids are the major component of cell
membranes
• Fatty acids, choline, as well as other substances
are bound in the phospholipid layer
Lipid Transport
• In the stomach
• In the intestine
• In the bloodstream, and the lymphatic system
Protein

Channel
 Hydrophilic
 Hydrophobic
 Hydrophilic
Functions
Emulsifiers
Lecithins are used by the food industry to:
• Combine foods that wouldn’t normally mix
• Increase dispersion and reduce fat
separation
• Increase shelf-life, prolong flavor release,
and prevent such products as gum from
sticking to teeth
Phospholipids in Foods
•
•
•
•
A typical diet contains only about 2 grams
per day
Lecithin (phosphatidylcholine) is the major
phospholipid and is found in:
Liver, egg yolk, soybeans, peanuts,
legumes, spinach, and wheat germ
Usually lost during food processing
Derived Lipids: STEROLS
•
•
•
•
Sterols are hydrocarbons with a multiple
ring structure
They are hydrophobic and lipophilic
Contain no fatty acids
Cholesterol is the best-known sterol,
found only in animal products
CHOLESTEROL: Functions
•
•
•
Major component of cell membranes
(especially abundant in nerve and brain
tissue)
Precursor molecule: Example - Vitamin D
and estrogen are synthesized from
cholesterol
Important in the synthesis of bile acids
CHOLESTEROL: Synthesis
•
•
•
•
The liver manufactures most of the
cholesterol in our bodies
The intestine and all cells contribute a
small amount
Overall, the body produces about 1000 mg
per day
Serum cholesterol levels are
homeostatically controlled (set-point)
DIGESTION
•
•
•
•
Mouth: chewing, lingual lipase, and dietary
phospholipids
Stomach: gastric lipase
Small Intestine: CCK = bile, Secretin =
pancreatic juice (pancreatic lipase)
Micelles: tiny emulsified fat packets that
can enter intestinal cells (enterocytes)
DIGESTIBILITY
•
•
•
•
•
Abnormal to find more than 6 or 7% of
ingested lipids still intact in the feces
Steatorrhea indicates fat malabsorption
Breast milk
Medium-Chain Trigylcerides
Short-Chain Fatty Acids
ABSORPTION
•
Most fat absorption takes place in the duodenum
or jejunum – micelles carry monoglycerides and
free fatty acids to the brush border where they
diffuse into enterocytes
• Bile salts are absorbed in the ileum (enterohepatic
circulation)
• Once in the enterocytes, monoglycerides and
free fatty acids are reformed into triglycerides
• The triglycerides, cholesterol, phospholipids,
and protein carriers form LIPOPROTEIN
ABSORPTION
•
•
•
•
•
Once these lipoproteins leave the cell, they become
CHYLOMICRONS and enter the lymph system
MCTs, short-chain fatty acids and glycerol are
absorbed directly into bloodstream. They do not
enter the lymph system.
Cholesterol and other sterols are poorly
absorbed. Overall, about 50% of dietary
cholesterol is absorbed.
Dietary fat increases cholesterol absorption
Fiber (especially soluble fiber) and phytosterols
decrease cholesterol absorption
triglycerides
Lipids in the Body
•
•
•
•
•
Chylomicrons
Very-Low-Density Lipoprotein
Intermediate-Density Lipoprotein
Low-Density Lipoprotein
High-Density Lipoprotein
 Chylomicrons
are lipoproteins
Heart Disease
•
•
•
More than 58 million Americans have at
least one form of CVD – stroke,
hypertension, or coronary heart disease
1 in 9 women, and 1 in 6 men aged 45-64
years of age have some form of heart
disease
Myocardial Infarction (heart attack) is the
leading cause of death in American men
and women
Atherosclerosis
•
A slow, progressive disease that begins in
childhood and takes decades to advance.
• Basically, plaque (lipid deposits and other
substances) forms in response to injuries on the
artery wall
• Plaque can eventually completely occlude the
artery leading to MI
• Injury can be caused by: hypercholesterolemia,
oxidized LDL, hypertension, smoking, diabetes,
homocysteine, and diets high in saturated fat
What Are the Lipid Related Risk
Factors for CVD?
•
•
•
•
High LDL Cholesterol and Low HDL
Cholesterol
A diet high in cholesterol
A diet high in saturated fat
A diet high in trans-fatty acids
Trans Fatty Acids
•
Trans fatty acids tend to raise total blood
cholesterol levels, but less than more saturated
fatty acids
• Trans fatty acids also tend to raise LDL
cholesterol and lower HDL cholesterol
• It is not clear if trans fats that occur naturally
have the same effect as those produced by
hydrogenating vegetable oils
• The Food and Drug Administration (FDA) has
proposed that the amount of trans fatty acids in
a food be included in the Nutrition Facts panel
 Ingredients:
enriched wheat flour, corn
syrup, whole oats, raspberry preserves,
sugar, partially hydrogenated soybean
and/or cottonseed oil, glycerin,
maltodextrin, honey, dextrose, natural and
artificial flavors, nonfat dry milk, sodium
alginate, wheat bran, modified corn starch,
salt, cellulose gum, potassium
bicarbonate, lecithin, citric acid, xanthan
gum, calcium phosphate, malic acid, whey
protein concentrate, red #40, blue #1.
Other Dietary Considerations
•
•
•
•
•
Homocysteine – high levels of this amino
acid may promote atherosclerosis,
excessive blood clotting, or blood vessel
rigidity
Omega-3 Fatty Acids
Soluble Fiber
Antioxidants – clean up free-radicals
(Vitamin E, Vitamin C, etc)
Other Phytochemicals – isoflavones and
lignans