The Lipids: Triglycerides, Phospholipids, and Sterols

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Chapter 5

• The Lipids Triglycerides, Phospholipids, and
  Sterols

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I. IntroductionII. Chemistry of Triglycerides
and Fatty Acids

• A. Fatty acids
• 1. Carbon chain
• a. Methyl end CH3 and a carboxyl end COOH

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Fatty Acid Structure
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Fatty Acid
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Fatty acids (cont)

• 2. Naming fatty acids
• a. omega (w) is from the CH3 end
• 1. w3 and the w6 fatty acids
• b. n is also from the CH3 end
• 1. Not widely used
• c. Delta (D) is from the COOH end
• 1. Not widely used

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Fatty acids (cont)

• 3. Degree of saturation
• a. Saturated (solid at room temperature RT)
• 1. Every carbon atom has as many hydrogens
  bound as possible
• 2. Stearic acid (C180), palmitic acid (C160)
• b. Unsaturated (liquid at RT)
• 1. There are carbons that do not have
  hydrogen atoms bound at every possible site
  rather the carbons form double bonds (an
  unsaturated bond) between them

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Saturated Fatty Acid
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Fatty acids (cont)

• 2. Monounsaturated (MUFA)
• a. There is one unsaturated bond between two of
  the carbons
• b. oleic acid (C181)
• 3. Polyunsaturated (PUFA)
• a. There is more than one unsaturated bond
• b. linoleic acid (C182), linolenic acid
  (C183), arachidonic acid (C204)

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Monounsaturated Fatty Acid
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Naming Fatty Acids
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Monounsaturated Fatty Acid
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Fatty acids (cont)

• 4. FA content of oils and fats
• a. Olive oil and canola oil (C181)
• b. Vegetable oils (soybean, cottonseed,
  safflower, corn, sunflower) (C182,3)
• c. Animal fats (lard /tallow) (C160, C180)
• d. Tropical oils (coconut / palm) (C100,
  C120)
• e. Fish oils (C205, C226)

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Fatty Acid Composition of Foods
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Fatty Acid Composition of Foods
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Fatty acids (cont)

• 5. Triglyceride formation
• a. Tri 3 fatty acids
• b. Glyceride glycerol
• c. Condensation reaction
• 1. 3 fatty acids attach to a molecule of
  glycerol

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Triglyceride Formation
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Glycerol
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Triglyceride Formation
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Triglyceride Formation
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B. Processed fats in foods

• 1. Hydrogenation of fats (adding hydrogen)
• a. Makes oils more solid
• b. Affects texture
• c. Affects stability of fat
• 1. Unsaturated bonds are unstable
• d. Trans-fatty acids produced
• 1. safety questions - Coronary Heart
  Disease (CHD)

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Hydrogenation
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Hydrogenation (cont)
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C. Role of triglycerides and fatty acids

• 1. In the body
• a. Provide energy
• b. Provide insulation
• c. Protect organs from trauma
• 2. In the diet
• a. Provide fat-soluble vitamins
• b. Provide flavor, aroma, tenderness to food
• c. Slow digestion---gt satiety and fullness

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D. Essential Fatty Acids

• 1. omega-6 (w6) (fatty acid
• a. linoleic (C182)
• 2. omega-3 (w3) fatty acid
• a. linolenic (C183)
• 3. Debate over essentiality
• a. Growth
• b. Disease
• 1. eicosapentanoic (C205) can be made
  from the w3 linolenic acid
• 2. arachidonic (C204) can be made from
  the w6 linoleic acid

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Essential Fatty Acids (cont)

• 4. PUFA requirements
• a. should make up to 3 of fatty acid
  intake b. PUFA deficiencies cause growth
  retardation, skin lesions, neurological and
  visual abnormalities
• 5. Role of polyunsaturated fatty acids
• a. w3 and w6 fatty acids are precursors to
  potent bioactive compounds
• 1. Prostaglandins
• a. Platelet antiaggregate
• 2. Thromboxanes
• a. Platelet aggregate

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III. Phospholipids and Sterols

• A. Chemistry of phospholipids (lecithin)
• 1. Polar and non-polar molecule
• a. Phospho polar group
• b. Lipid non-polar group
• 2. Enables the mixing of polar (water) and
  non-polar (oil and fat) compounds
• a. Food such as Mayonnaise and candy

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Lecithin
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Chemistry of phospholipids (lecithin) (cont)

• 3. Role of phospholipids
• a. in cell membranes
• 1. Required for development of membrane
  (phospholipid bilayer)
• 2. Function in control of cell cell
  adherence
• 3. Allow movement of lipids across cell
  membrane

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B. Chemistry of sterols (steroidal compounds)

• 1. Structure
• a. made up of multiple rings
• b. Steroid nucleus
• 2. Sterols in foods
• a. Plants and animal foods contain sterols
• b. Cholesterol only found in animal products
• 1. Eggs and organ meats very high sources
  (eggs 250 mg)

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Compounds Derived From Cholesterol
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Chemistry of sterols (steroidal compounds) (cont)

• 3. Role of sterols
• a. Bile acids
• 1. Fat metabolism
• 2. Polar and non-polar groups
• b. Sex hormones
• 1. Estrogen
• 2. testosterone
• c. Adrenal hormones
• 1. Corticosteroids
• d. Vitamin D

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Compounds Derived From Cholesterol
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IV. Digestion, Absorption and Transport

• A. Digestion
• 1. Mouth
• a. Lingual lipase
• 1. Secreted by salivary glands (active in
  infants, little activity in adults)
• b. Body temperature
• 2. Stomach
• a. no digestion

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Digestion (cont)

• 3. Small intestine
• a. Fat entering the small intestine
  stimulates the release of cholecystokinin
  (CCK) which causes the gallbladder to contract
  secreting bile into the small intestine
• b. Emulsification
• 1. Bile
• a. Synthesized in the liver
• b. Stored in the gallbladder

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Emulsification (cont)

• c. Secreted into the common bile duct
• d. Enables fats and water to mix
• 1. Lipases function in a water environment
• e. Can be reabsorbed (enterohepatic
  circulation)
• (entero intestine, hepatic liver)
• c. Digestion
• 1. Pancreatic lipase
• a. TG º FA FA FA glycerol

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Bile An Emulsifier

• Bile enables fat and water to mix (emulsify).
  This is critical as enzymes involved in fat
  digestion are located in the water environment of
  the small intestine and fats must be in proximity
  to the enzymes for hydrolysis to occur. Bile
  also facilitates fat absorption by forming
  spherical molecules (micelles) that contain fat.
  Micelles interface with the cell membrane of
  intestinal cells allowing fat to diffuse into the
  cell.

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Fat Digestion (Hydrolysis Reaction)
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B. Absorption

• 1. Bile assists in the absorption of long
  chain fatty acids (micelle formation)
• a. long-chain FA º micelle º intestine º TG º
  chylomicron ºº lymph º thoracic duct º left
  subclavian vein º blood
• b. glycerol, monoglycerides and short-chain
  FA º intestine º blood

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Fat Absorption
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C. Transport

• 1. Chylomicron
• a. A water soluble transport vehicle for
  dietary fatty acids (one of four
  lipoproteins)
• b. Synthesized in the intestinal cell
• 1. Consists of TG, protein and cholesterol
• c. Transports dietary fat to cells
• d. Chylomicron remnant goes to liver for
  destruction

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Lipoprotein
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Transport (cont)

• 2. Very low density lipoprotein (VLDL)
• a. newly made TG from liver
• 1. Excess carbohydrates
• 2. Excess protein
• 3. Consists of TG, protein and cholesterol
• b. transport fat to cells
• c. VLDL remnant becomes LDL

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Transport (cont)

• 3. Low density lipoprotein (LDL)
• a. transports cholesterol to cells
• b. need some but most have too much
  cholesterol
• 1. Lifestyle
• 2. Genetics
• c. bad cholesterol
• 1. increases cholesterol build-up in arteries

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Transport (cont)

• d. dietary effects on LDL
• 1. saturated fat increase LDL
• 2. polyunsaturated fat decreases LDL
• 3. monounsaturated fat decreases LDL
• 4. vegetable protein decreases LDL
• 4. High density lipoprotein (HDL)
• a. transports cholesterol away from arteries
  to liver
• b. good cholesterol
• c. dietary effects
• 1. MUFA possibly increase

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Transport (cont)

• d. lifestyle effects on HDL
• 1. exercise increases
• a. Vigorous
• b. 10-20 increases

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Lipoprotein Composition
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V. Metabolism of Lipids in the Body

• A. Function
• 1. Energy
• a. Lipids circulate in the blood and provide
  energy for cells
• 1. Requires oxygen and some CHO
• b. Supplies 60 of energy need during rest
• 2. Insulation
• a. Lipids serve as an insulator

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Function (cont)

• 3. Transport
• a. Transport of fat soluble vitamins
• 4. Building materials
• a. Cell membranes
• b. Cholesterol
• 1. Hormones
• 2. Glucocorticoids
• c. Bioactive compounds
• 1. Prostaglandins
• 2. Thromboxanes

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B. Fat storage

• 1. Body efficiently converts dietary fat to
  storage fat
• 2. Unlimited capacity to synthesize and
  store fats
• a. Excess CHO can be converted into fat
• b. Excess protein can be converted into fat
• 3. Fats are stored in adipose tissue
• 4. One pound of fat equals 3500 kcal

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Fat Cell (Adipose Cell)
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Lipids and Fat Cells
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VI. Health Effects and Recommended Intakes of
Lipids

• A. Lipids and coronary heart disease (CHD)
• 1. Positive association with saturated fat
• a. Saturated fat is hypercholesterolemic
• 2. Positive association with cholesterol
  (LDL)
• 3. Negative association with MUFA
• a. Raise HDL

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Lipids and coronary heart disease (CHD) (cont)

• 4. Negative association with PUFA
• a. omega-3 fatty acids
• 1. decrease cholesterol
• 2. found in fish oils
• 3. reduce blood clotting
• 4. reduce blood pressure?
• 5. Positive association with trans fatty
  acids (hydrogenation)

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B. Cholesterol and CHD

• 1. LDL cholesterol directly correlates with
  CHD
• 2. HDL inversely correlates with CHD
• 3. moderate alcohol consumption associated
  with reduced risk of CHD (increases HDL)

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Cholesterol and CHD (cont)

• 4. Oxidized cholesterol may promote plaque
  formation (atherosclerosis)
• a. Antioxidant research inconclusive
• 1. vitamin C
• 2. Carotene
• 3. vitamin E

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C. Atherosclerosis

• 1. Plaque development
• a. Injury of artery followed by cell
  migration and cholesterol deposition
  eventually forming a hard plaque
• b. blood clots
• 1. Dislodgement of piece of plaque
• 2. infarction (heart)/stroke(brain)
• c. Positive association with cholesterol

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Atherosclerosis and CHD
Atherosclerosis is a chronic condition in which
the arteries are laden with fatty streaks. Fatty
streaks can harden and form plaques which can
eventually occlude the passage of blood. If this
occurs in one of the coronary arteries a heart
attack ensues.
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D. Recommended fat intakes

• 1. 30 of total kcal intake
• 2. 10 of total kcals from
• a. saturated (decrease)
• b. PUFA (w3 especially)
• c. MUFA (increase)
• 3. 300 mg or less of cholesterol
• 4. reduce fat in diet (American average
  intake38-42)

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E. Risk factors for heart disease

• 1. Smoking
• 2. Hypertension
• 3. high blood cholesterol
• a. high LDL cholesterol
• b. low HDL cholesterol
• 4. lack of exercise

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Risk factors for heart disease (cont)

• 5. Obesity
• 6. Stress
• 7. heredity
• 8. male gender

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F. Recommendations

• 1. Diet
• a. STEP 1
• 1. total fat only 30 of dietary calories
• 2. saturated fat only 10 of total calories
• 3. cholesterol less than 300 mg/day
• b. STEP 2
• 1. further reductions in fat and cholesterol

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Recommendations (cont)

• c. STEP 3
• 1. diet and drug therapy
• 2. Physical activity
• a. Frequent
• b. sustained

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G. Fat Alternatives ( fat alternatives at FDA)

• 1. Oatrim and other carbohydrate based fat
  replacements
• 2. Simplese and other protein based fat
  replacements
• 3. Olestra and other fat based fat
  replacements