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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

• A broad range of organic compounds that dissolve easily in organic solvents, but range in their solubility in water
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Hydrophobic – “water-fearing”
Lipophilic – “fat-loving”

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SIMPLE LIPIDS
Fatty Acids
Triglycerides
Waxes
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COMPOUND LIPIDS
Phospholipids
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DERIVED LIPIDS
Sterols

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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

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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

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

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SATURATION
UNSATURATED FATTY ACID = If adjoining carbons are joined by double bonds

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UNSATURATED
One double bond = monounsaturated fatty acid
Two or more double bonds = polyunsaturated fatty acid

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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

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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

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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

NOMENCLATURE
• Alpha and Omega
• 18:0, 18:1, etc.

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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 9 th carbon from the methyl end, so we must get these fatty acids from our diet
EFAS = omega-6 linoleic acid & omega-
3 alpha-linolenic acid

• Omega-3: Alpha-Linolenic Acid (ALA),
Eicosapentaenoic Acid (EPA),
Docosahexaenoic Acid (DHA)
• Omega-6: Linoleic Acid, Arachidonic
Acid

• Flaxseed, soybean oil, walnuts, some leafy dark green vegetables (ALA)
• Fatty fish: salmon, tuna, and mackerel, fish oils (EPA and
DHA)

• Seeds, nuts, common vegetable oils: corn, safflower, cottonseed, sunflower seed, peanut (linoleic acid)
• Meat (arachidonic acid)

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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

Omega-6s
• Linoleic acid is converted to arachidonic acid and eicosanoids are formed.
• Overall effect: constricting blood vessels, promoting inflammation and blood clotting

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

STRUCTURE
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Triglyceride - three fatty acids attached to a glycerol backbone
Diglyceride – two fatty acids +glycerol
Monoglyceride – one fatty acid
+glycerol

Fatty Acids Triglyceride

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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

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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

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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

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Channel
 Hydrophilic
 Hydrophobic
 Hydrophilic
Protein

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Emulsifiers
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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

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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

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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

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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

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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)

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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)

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• 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

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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

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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

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• Chylomicrons
Very-Low-Density Lipoprotein
Intermediate-Density Lipoprotein
Low-Density Lipoprotein
High-Density Lipoprotein

 Chylomicrons are lipoproteins

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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

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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

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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

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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.

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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