The Lipids: Triglycerides, Phospholipids and Sterols

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The LipidsTriglycerides, Phospholipids and
Sterols
Chapter 5
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Lipids

• Family of compounds that includes
• Triglycerides fats oils
• Phospholipids
• Sterols
• Composed of C, H, O
• ? C H ? energy/gram

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Triglycerides

• Triglycerides are composed of
• One glycerol molecule
• Glycerol is a 3-carbon alcohol that is the
  backbone of a triglyceride
• Three fatty acid molecules
• Fatty acids are long chains of carbon atoms
  surrounded by hydrogen atoms
• Acid group at one end
• Methyl group at other end
• Most TG contain mixture of gt1 type of fatty acid

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Glycerol
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TG made from glycerol 3 FA
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Formation of TG through Condensation
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Hydrolysis of TG
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Classification of TG

• Length
• Saturation
• Shape

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Chain Length

• Short-chain FA are lt 6 C.
• Medium-chain FA are 6 - 12 C.
• Long-chain FA are gt 14 C.
• Most naturally occurring fatty acids contain even
  numbers of carbons in their chains

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Level of saturation

• Saturation refers to how many hydrogen atoms
  surround each carbon
• Saturated fatty acids (SFA)
• Fully loaded with H atoms Only single bonds b/w
  C atoms
• Monounsaturated fatty acids (MUFA)
• Carbons without hydrogen must bond ? forms double
  bond between Cs
• MUFAs have 1 double bond
• Polyunsaturated fatty acids (PUFA)
• gt 2 C to C double bonds
• Identified by position of double bond nearest
  methyl end

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Stearic acid (SFA)
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Oleic acid (MUFA)
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Linoleic acid (PUFA)
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Shape

• Molecules of SF have no double C bonds form
  straight, rigid chains.
• Each double bond of UF bends them along their
  length.
• A cis FA has both H located on same side of
  double bond.
• In a trans FA, H are attached on diagonally
  opposite sides of the double bond.
• Process of hydrogenation
• Double bonds are broken additional H is added.

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Cis Trans-FA
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Trans-FA

• Trans configuration affects function in body
• Behave much like SFAs
• Adverse health effects
• Conjugated Linoleic Acid
• Naturally occurring trans-fatty acid
• May have health benefits

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Chemical Properties

• Firmness
• Depends on degree of saturation
• Saturated straight, packs tightly, solid at room
  temperature
• Animal fats solid SFA from vegetable sources
  softer due to shorter chains
• Stability
• Polyunsaturated fats spoil most readily because
  double bonds least stable to oxidation
• Impact of Hydrogenation
• Protects against oxidation, makes vegetable oils
  more solid

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Chemical Properties
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Phospholipids

• Phospholipids
• Are composed of
• Glycerol backbone
• 2 fatty acids
• Phosphate
• Are soluble in water
• Are manufactured in our bodies so they are not
  required in our diet

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Lecithin

• Most well known phospholipid
• A compound of glycerol to which are attached 2
  FA, a phosphate group, and a choline molecule.
• Used as an emulsifier to combine 2 ingredients
  that do not ordinarily mix.
• Found in egg yolk, liver, soybeans, wheat germ,
  peanuts.

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Role of Phospholipids

• Important constituents of cell membranes
• Help lipids, fat soluble vitamins and hormones
  cross membranes into watery fluids on both sides
• Act as emulsifiers in blood -- keeps lipids
  (TG,cholesterol) suspended

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Phospholipids
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Sterols

• Compounds containing 4 carbon ring structure with
  any of a variety of side chains
• Many important body compounds are sterols
• cell membranes, bile acids, sex adrenal
  hormones, vit D cholesterol.
• Sterols are found in plant animal foods
• Manufactured in bodies so non-essential

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Sterols

• Animal Sterols
• Significant amounts of cholesterol
• Meat, eggs, fish, poultry, dairy products
• Difference b/w dietary blood cholesterol
• Plant Sterols
• Interfere with cholesterol absorption

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Cholesterol

• A structural component of cell membranes used
  to synthesize key compounds.
• Synthesized by liver - endogenous cholesterol.
• Dietary cholesterol -exogenous cholesterol.

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Cholesterol
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Digestion of Lipids

• Aim to dismantle triglycerides into small
  molecules
• Monoglycerides
• Fatty acids
• Glycerol
• Digestive enzymes are in water solution.
• Fats and water dont mix.
• How can enzymes come in contact with lipids?

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Begins in Mouth

• Minor role in fat digestion
• Hard fats begin to melt when reach body
  temperature
• Salivary glands release lingual lipase which
  begins break down (digestion) of fat
• Minimal action in adults
• More active role in infants in breaking down milk
  fat

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In the stomach

• Fat floats on watery layer of contents which
  limits fat digestion
• Stomach churns contents mixing fat within watery
  contents.
• Breaks up fat into smaller pieces or droplets
• Helps expose fat to gastric lipase enzymes
  works primarily on short chain fatty acids.

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In the small intestine

• Fat enters the SI, (1) cholecystokinin (CCK)
  signals the gallbladder to release bile -- (bile
  salts) an emulsifier (2) pancreas secretes
  lipase--an enzyme
• One end of bile salt is an amino acid which
  attracts water the other end is a sterol ring
  which attracts lipid -- acts as an emulsifier
  (lipid-in- water)
• Enzyme can now come in contact with fat as they
  are mixed within the watery contents.

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Bile Acid
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What happens to bile salts?

• May be reabsorbed from the intestine and
  recycled, or
• May be trapped by dietary fibres in colon
  eliminated. Pectins gums are most effective
• Cholesterol is required to make bile salts.
  Eliminating bile salts can help reduce high blood
  cholesterol levels

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Hydrolysis of Lipids

• Enzymes break down TG to 1MG and 2 fatty acids,
  and sometimes down to glycerol and the 3rd FA
• FAs, MG, and glycerol can be absorbed into
  intestinal cell wall
• PL hydrolyzed similarly
• Cholesterol absorbed as is

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Small Intestine - Absorption

• Small molecules (glycerol, short medium chain
  FAs) diffuse easily to intestinal cells into
  blood stream where transported on blood proteins
  or phospholipids
• Monoglycerides long-chain FAs are arranged as
  lipoproteins for absorption and transport.
• Micelles spherical complexes formed by molecules
  of bile surrounding monoglycerides fatty acids
  transport them for absorption
• Once inside intestinal cells FAs put back
  together into TG packaged into lipoproteins.
• Specific LP produced to transport fat are called
  chylomicrons
• Chylomicrons released to lymphatic system
• Enter blood stream at thoracic duct

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Absorption
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Transporting Fats

• Lipoproteins
• clusters of lipids associated with proteins that
  serve as transport vehicles for lipids in the
  lymph and blood
• 4 types - each contains different kinds and
  amounts of proteins and lipids.

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Chylomicrons

• Contains largest amounts of TG.
• Cells remove lipids from chylomicrons as they
  pass by.
• Protein receptors on membranes of liver cells
  remove chylomicrons from blood.
• Liver cells dismantles them use them or
  recycles pieces.

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Very-Low-Density Lipoproteins (VLDL)

• Made by liver cells to transport lipids to
  various tissues.
• As they lose TG, become denser.
• Low Density Lipoprotein (LDL)
• Derived from VLDL, ½ cholesterol.
• As they circulate, make contents available to
  cells of all tissues.
• Liver has special LDL receptors, which control
  blood cholesterol concentration.
• Commonly known as bad cholesterol

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High Density Lipoprotein (HDL)

• Transports cholesterol back to liver from cells
  (scavenger).
• 45-50 protein.
• Commonly known as good cholesterol

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3 primary fates of dietary fat

• Can immediately be taken up and used as a source
  of energy for cells.
• Can be used to make lipid-containing compounds in
  body.
• Can be stored in adipose tissue as TG for later
  use.

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The Role of Fats

• Triglycerides a key source of energy
• Fat carbohydrate required for energy metabolism
• Adequate fat CHO spares protein
• 1 pound of body fat provides 3500 kcal.
• Fat used for energy storage.
• Much of the energy used during rest comes from
  fat.
• Fat is used for energy during exercise,
  especially after glycogen is depleted.

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The Role of Fats

• Fat is essential to many body functions
• Cell membrane structure
• Nerve cell transmissions
• Protection of internal organs
• Insulation to retain body heat
• Fat-soluble vitamins
• Vitamins A, D, E, and K are soluble in fat fat
  is required for their transport

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The Role of Fats

• Fat provides flavour and texture to foods.
• Fat contributes to making us feel satiated
  because
• Fats are more energy dense than carbohydrates or
  protein
• Fats take longer to digest

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Lipids in the Body

• Essential fatty acids
• Two fatty acids cannot be synthesized in the body
  and must be obtained in the diet
• Omega-3 fatty acid family
• Primary memberAlpha-linolenic acid
• Precursor to Eicosapentaenoic acid (EPA)
  Docosahexaenoic acid (DHA)
• Found in vegetables, fish fish oils
• Omega-6 fatty acid family
• Primary member Linoleic acid
• Precursor to Arachidonic Acid (AA)
• Found in vegetable and nut oils

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Lipids in the Body

• Eicosanoids
• Arachidonic acid EPA used to make eicosanoids
• Hormonelike - prostaglandins, thromboxanes
  leukotrienes
• EPA ecosanoids ? blood pressure, prevent blood
  clot formation, protect against irregular
  heartbeats ? inflammation
• Arachidonic acid ecosanoids less beneficial
• BALANCE of essential fatty acids critical

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Lipid Metabolism

• Storing Fat as Fat - Adipose Tissue
• Lipoprotein lipase (LPL)
• Found on surface of fat cells.
• Capture TG from LP passing by hydrolyzes them.
• If needed, FA quickly transported into
  mitochondria used as fuel.
• Inside cells, other enzymes reassemble pieces
  into TG for storage.

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Lipid Metabolism

• Making Fat from CHO or Protein
• FA can be made from 2 carbon chains derived from
  any energy nutrient.

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Lipid Metabolism

• Using Fat for Energy
• Hormone-sensitive lipase
• found inside adipose cells
• Dismantles triglycerides release glycerol
  fatty acids directly to blood stream
• Used by cells requiring energy
• Brain, nerves red blood cells require glucose
• Only glycerol can be converted to glucose
  produce ketone bodies
• Cannot sustain life alone

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Health Effects

• Cardiovascular disease
• Dysfunction of the heart or blood vessels
• Can result in heart attack or stroke
• The type of fat in our diet can contribute to or
  protect against cardiovascular disease.

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Cardiovascular Disease

• Risk factors for cardiovascular disease include
• Being overweight
• Physical inactivity
• Smoking
• High blood pressure
• Diabetes

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Cardiovascular Disease

• Diets high in saturated fats
• Decrease the removal of LDLs from the blood
• Contribute to the formation of plaques that can
  block arteries
• Increase triglyceride levels (chylomicrons and
  VLDLs)

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Cardiovascular Disease

• Trans fatty acids
• Can raise LDL cholesterol levels as much as
  saturated fat
• Also decrease HDL cholesterol levels
• Are abundant in hydrogenated vegetable oils
  (margarine, vegetable oil spreads)
• Should be reduced to the absolute minimum

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Cardiovascular Disease

• Dietary Cholesterol
• Does raise blood cholesterol but effects less
  than SFAs
• Most foods high in cholesterol also high in
  saturated fats
• Except eggs
• One egg/day for someone with normal blood lipid
  profile acceptable

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CVD - Atherosclerosis
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Cardiovascular Disease
Cross-section of (a) a normal artery and (b) a
partially blocked artery.
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Cardiovascular Disease

• How can fat intake protect against heart disease?
• Replacing SFA TFA with mono- poly- UFA may be
  most effective dietary strategy to prevent CVD
• Diets high in omega-3 fatty acids (along with
  moderate exercise) can increase HDL good
  cholesterol levels.
• Dietary sources fatty fish functional foods
• Caution re supplement use

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Health Effects

• Cancer
• Possible associations between dietary fat intake
  cancer
• Not an initiator of cancer but may promote cancer
  once it has arisen
• SFA from meats associated with cancer promotion
• Omega-3 FA may protect against cancer

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Health Effects

• Obesity
• High fat consumption generally equates to excess
  energy intake
• Especially if inactive
• Cutting fat can effectively cut calories
• Watch for what replaces fat in food products

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How Much Fat?

• The Acceptable Macronutrient Distribution Range
  (AMDR) for fat
• 20-35 of Calories should be from fat
• Athletes highly active people may need more
  energy from carbohydrates and can reduce their
  fat intake to 20-25 of total Calories.

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How Much Fat?

• The type of fat consumed is important.
• Saturated fat should be no more than 7 of total
  Calories.
• Trans fatty acids should be reduced to the
  absolute minimum.
• Most fat in our diets should be from
  monounsaturated fats (e.g., olive oil).

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How does our diet compare?

• Fat accounts for an average of just over 31 of
  Canadians daily calories but over ¼ of Canadians
  aged 31 to 50 get more than 35 of their total
  calories from fat.

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How Much Fat

• Linoleic acid
• AI
• 14-18 yr males 16 g/day females 11 g/day
• 19-50 yr males 17 g/day females 12 g/day
• gt50 yr males 14 g/day females 11 g/day
• a-linolenic acid
• AI
• 14-gt50 yr males 1.6 g/day
• 14-gt50 yr females 1.1 g/day

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Recommendations for adults
Up to 10 of the AMDR for Linolenic acid (0.06
- 0.12 of total energy) can be consumed as EPA
/or DHA.
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From Guidelines to Groceries

• Choose vegetables fruit prepared with little or
  no added fat, sugar or salt.
• Choose grain products that are lower in fat,
  sugar or salt
• Drink skim, 1 or 2 milk each day.
• Select lower fat milk alternatives.
• Have meat alternatives such as beans, lentils
  tofu often.
• Eat at least 2 Food Guide Servings of fish each
  week.
• Select lean meat alternatives prepared with
  little or no added fat or salt
• Look for round or loin cuts
• Grill, roast, broil, bake, stew or braise
• Include a small amount of unsaturated fat limit
  amount of saturated trans fats in diet.

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From Guidelines to Groceries

• Visible fats
• Fats we knowingly add to foods
• Butter, cream, mayonnaise, dressings
• Invisible fats
• Fats hidden in foods
• Naturally occurring or added during processing
• i.e. marbled fats in meats, fried deep-fried
  foods, baked goods

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From Guidelines to Groceries

• Butter
• Rich in SF and cholesterol

• Margarine
• Low in SF but may contain TFA
• No cholesterol
• Choose carefully
• Look for non-hydrogenated soft tub margarines

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From Guidelines to Groceries

• Low fat products
• Can significantly reduce amount of fat consumed
  if incorporated in diet on regular basis but may
  or may not reduce the amount of energy consumed.
• If you want to reduce both the amount of fat and
  the of kcal you consume, you must read
  nutrition facts table carefully before you buy.

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From Guidelines to Groceries

• Mercury in fish
• Health Canada guidelines
• For fresh and frozen tuna, shark, swordfish,
  escolar, marlin and orange roughy
• General population can eat up to 150 g per wk.
• Women who are or may become pregnant and
  breastfeeding mothers can eat up to 150 g per
  month.
• Children between 5 11 yrs of age can eat up to
  125 g per month. Children between 1 4 yrs of
  age should eat no more than 75 g per month.

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From Guidelines to Groceries

• Mercury in fish
• Health Canada guidelines
• For canned albacore tuna
• Women who are or who may become pregnant, or who
  are breastfeeding can eat up to 4 Food Guide
  Servings each wk.
• Children between 1 4 yrs old can eat up to 1
  Food Guide Serving each wk. Children between 5
  11 yrs old can eat up to 2 Food Guide Servings
  each wk.

http//atn-riae.agr.ca/seafood/health_safety_e.htm

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In-Class Activity

• Many health organizations are calling on
  governments to ban the use of trans fats in
  foods.
• Do you think trans fats should be banned? Why or
  why not?
• Who would benefit from a ban on trans fats? Who
  would be harmed by a ban on trans fats?

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Next

• Chapter 6
• Protein Amino Acids