Lipids

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Lipids

• Triglycerides, phospholipids, sterols

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Chemical composition of fats

• Carbon-abundant
• Hydrogen-most abundant
• Oxygen-little

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Triglycerides

• Are made from one molecule of glycerol and three
  fatty acid

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Fatty acids

• Contain 4-24 carbons
• 18 carbon fatty acids are the most common in food
• The types of fatty acids that attach to the
  glycerol determine the uniqueness of each
  triglyceride
• Butter, olive oil and lard are all triglycerides,
  but differ from one another

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Fatty acids

• Saturated
• Carbons are surround by as much hydrogen as
  possible
• They are saturated with hydrogen
• Unsaturated
• One (monounsaturated) or more (polyunsaturated)
  carbons has less than maximum amount of hydrogen

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Important polyunsaturated fatty acids

• Omega 3 fatty acids
• First point of unsaturation is next to the third
  carbon from the tail of the fatty acid
• Linolenic acid
• Omega 6 fatty acids
• First point of unsaturation is next to the sixth
  carbon from the tail of the fatty acid
• Linoleic acid

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Firmness of a triglyceride

• Polyunsaturated oils are liquid at room
  temperature
• Found in plants
• Saturated triglycerides are solid at room
  temperature
• Found in animals
• Found in cocoa butter, palm oil, palm kernel oil,
  coconut oil
• Softer than animal saturated fats due to shorter
  chain fatty acids (4-14 carbons)

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Stability of triglycerides

• Saturated fats are more stable because they react
  less with oxygen
• Less stable unsaturated fats can have
  preservatives that compete with oxygen ( BHA,
  BHT, vitamin E),need to be refrigerated,
  protected from light and air, or hydrogenated to
  prolong shelf life

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Hydrogenation

• In the manufacturing process hydrogen reacts with
  polyunsaturated plant oils and saturates some of
  the carbons with hydrogen
• Resulting product is more solid and stable
• Produces trans fats

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Artificially produced trans fatty acids

• Some of the remaining double bonds become
  misshapen.
• Hydrogens are on opposite sides of double bond
• Trans fatty acids behave like saturated fatty
  acids and are linked to cardiovascular disease

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Naturally occuring trans fatty acids

• May have health benefits
• Conjugated linoleic acid

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Phospholipids

• Glycerol attached to 2 fatty acids and a
  different chemical in the 3rd position
• Best-known phospholipid is lecithin
• Choline is in the third position
• Body manufactures enough, so supplements are not
  necessary

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Properties of phospholipids

• Can dissolve in fat and water

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Functions of phospholipids

• Primary component of cell membranes
• Used as an emulsifier in processed foods

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Sterols

• Based on 4 rings of carbon
• Most important dietary sterol is cholesterol in
  animal products

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Cholesterol

• Mother molecule for many important molecules in
  body, including sex hormones and vitamin D, which
  is needed for calcium absorption
• The liver produces cholesterol, so none is needed
  in the diet
• bad cholesterol is associated with heart disease

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Lipid digestion

• Mouth
• Fats soften
• Lingual lipase
• In adults minimal digestion
• In infantssignificant digestion of short and
  medium chain fatty acids of milk

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• In stomach
• Slight amount by gastric lipase
• In small intestine
• Site of most fat digestion
• Triggers release of CCK
• CCK causes gall bladder to release bile

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• Bile is made of cholesterol and an amino acid and
  associated sodium, potassium or calcium as bile
  salt
• Bile is attracted to both fat and water
• Bile emulsifies fat so it can remain suspended in
  the watery fluid of the s.intestine as tiny
  droplets
• More fat is exposed to enzymes in the emulsified
  state

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Products of fat digestion

• Glycerol
• Fatty acids
• Monoglycerides
• Diglycerides

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Products of phospholipid digestion

• Glycerol
• Choline
• Fatty acids
• Monoglycerides
• Diglycerides

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Biles destiny

• Most of the bile is returned to the liver and
  then to the gall bladder and is used again
• Some bile can be trapped by dietary fiber,
  especially soluble fiber, and be carried out of
  the body

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Lipid absorption

• Glycerol, short chain and medium chain fatty
  acids go directly into blood of the capillaries
  of the villi
• Long chain fatty acids and monoglycerides merge
  together and are coated with bile to form
  micelles, which can remain suspended in water,
  travel to intestinal cell and diffuse into
  intestinal cell
• Inside the cell the products of digestion are
  reassembled into triclycerides and the bile
  reenters the lumen of the intestine

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• Inside the intestinal cells the new triglycerides
  are packed together along with cholesterol and
  phospholipids to form chylomicrons
• Chylomicrons enter the lymph vessels of the villi
• Lymph enters general circulation of blood
• Lipids are delivered to the cells of the body for
  immediate use or for storage

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Lipoproteins

• Clusters of lipids and proteins are used to
  transport fats in the blood stream
• Solve problem of transport through a watery fluid

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Types of lipoproteins

• 1. Chylomicrons
• Largest
• Least dense
• Transport lipids derived from diet
• Cells remove lipids from them over about a 14
  hour period, so they get smaller as time passes
• When depleted only cholesterol, protein remnants
  and phosphlipids remain
• The depleted chylomicrons are removed from
  circulation by the liver
• The liver dismantles them and uses or recycles
  the pieces

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• 2. VLDL ( very low density lipoproteins)
• Lipids made in the liver together with
  chylomicron remnants
• Released by liver into circulation
• Cells remove triglycerides
• VLDL shrink and become denser with a high ratio
  of cholesterol
• Eventually is transformed into LDL (low density
  lipoprotein

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• 3. LDL (low density lipoprotein)
• Circulate in blood
• All body cells remove cholesterol, phospholipids
  and remaining triglycerides to make membranes,
  hormones, etc
• Liver has receptors for LDL and removes what
  remains from circulation

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• 4. HDL (high density lipoprotein)
• Made by liver
• Carries cholesterol released along with fatty
  acids, triglycerides and fatty acids from fat
  cells back to liver
• Liver recycles or disposes cholesterol

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LDL vs. HDL

• Proportions and types of lipids and proteins are
  different
• Cholesterol component is chemically the same in
  both

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Sources of cholesterol in body

• Liver
• Diet

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Health implications

• LDL
• Bad cholesterol
• Linked to higher risk of heart attack
• HDL
• Good cholesterol
• Possibly protective of heart
• Represents cholesterol returning to liver for
  disposal

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Factors that lower LDL or raise HDL

• Weight control
• Monosaturated or polyunsaturate dietary fat
• Soluble dietary fiber
• Phytochemicals (plant compounds)
• Moderate alcohol consumption
• Physical activity

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Roles of lipids in body

• Triglycerides
• Energy
• Temperature insulation
• Protection as against shock
• Phospholipids
• Cell membranes
• Cholesterol
• Hormones

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Essential fatty acids

• Cannot be produced by body and must be provided
  in diet
• Plant oils are a good source
• Linoleic acid (omega 6)
• Linolenic acid (omega 3)

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Omega 3 and omega 6 fatty acids

• Omega 3
• Reduces risk of heart attack and stroke
• Found in
• Canola, soybean and flaxseed oils
• Walnuts
• Fatty fish (mackerel, salmon, sardines)
• Functional foods
• Omega 6
• Found in
• Vegetable oils
• Meat, poultry fish
• Functional foods

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Fat DRI

• 20-35 of energy intake
• Should be primarily from mono and polyunsaturated
  fat

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Fat substitutes

• Olestra
• Sucrose replaces glycerol
• Passes unchanged through body
• Can remove fat soluble vitamins from body

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The end