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The Lipids

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					     The Lipids:
    Triglycerides,
Phospholipids & Sterols
        Chapter 5
           Section Overview
 The Chemist’s View
  – Fatty Acids & Triglycerides
  – Phospholipids & Sterols
 Digestion, Absorption, & Transport
 Lipids in the Body
 Health Effects & Recommendations for
 Lipid Intake
                     Lipids

 Family of compounds that includes
  – Triglycerides (fats & oils)
  – Phospholipids
  – Sterols
 Composed of C, H, & O
  – ↑ C & H = ↑ energy/gram
The Chemist’s View: Fatty Acids
 Organic compounds
 Chain of Cs with Hs, an acid group at one
 end (COOH) and methyl at the other (CH3)
  – Differentiated by length of chains
 Fatty acids can be saturated or
 unsaturated
Classification of Fatty Acids

 Length short or long chain.
 18 carbon chains most common in human
 nutrition

 Saturation


 Shape –cis vs. trans
                Chain Length
 Short-chain FA are < 6 Carbon.


 Medium-chain FA are 6 - 12 Carbon.


 Long-chain FA are > 14 C.


  – Most naturally occurring fatty acids contain
    even numbers of carbons in their chains
  – Always come in even numbers, cleave 2 off at a time
    when eat them
          Saturated Fatty Acids




 Chain is fully saturated
   – Maximum number of Hs attached
   – Example, Stearic acid (animal sources)
   – Most food contain a mixture of saturated fatty acids
        Unsaturated Fatty Acids




 Chain is not fully saturated
   – Hs are missing
   – Double bonds form to satisfy Cs bonds (needs 4)
   – Example oleic acid (plant oils)
   – Would be a little twisted at the double bond in a 3-D
     form
       Degree of Unsaturation
 Monounsaturated (MUFA)
  – Mono= One
  – Single double bond
  – Less prevalent in food supply. One good source=
    olive oil. (and avocado)
 Polyunsaturated (PUFA)
   – Poly= Many
   – Multiple double bonds
   – Example linoleic acid (plant oils) (omega 6) First
     double bond occurs in the 6 carbon (is why its called
     omega 6)
           Omega Fatty Acids
 Describes location of
  double bonds
  – First one from methyl
    (CH3) end
 Common omega fatty
  acids
  – Omega-3 (linolenic)
  – Omega-6 (Linoliec)
           Cis & Trans-FA
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. (make it more saturated)
Cis & Trans-FA
          The Chemists' View
           Triglycerides (TG)
 Triglycerides are composed of:
  – One glycerol molecule
     Glycerol is a 3-carbon alcohol that is the backbone
      of a triglyceride
                         +
  – Three fatty acid molecules
     Most TG contain mixture of >1 type of fatty acid
TG - Glycerol
TG made from glycerol +
         3 FA
Formation of TG through
    Condensation
Hydrolysis of TG
                   Shape
 Molecules of Saturated Fat
 have no double C bonds &
 form straight, rigid chains.

 Each double bond of
 Unsaturated Fat bends them
 along their length.
          Chemical Properties of
              Triglycerides
 Firmness
   – Depends on degree of saturation
   – Saturated straight, packs tightly, solid at room
     temperature saturated = solid at room temp
   – 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
Chemical Properties
Fat Composition
 The Chemist’s View: Phospholipids
 Similar to triglycerides
   – Two fatty acids + a phosphate (on the 3rd C)
   – Phosphate is attached to a N containing group, such
     as choline
   – Are soluble in water
   – Are manufactured in our bodies so they are not
     required in our diet
   – Can be hydrophobic (fat) and hydrophilic (protein)
   Phospholipids: 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.
            Role of Phospholipids
 Important constituents of
  cell membranes

 Help lipids, fat soluble
  vitamins & hormones cross
  membranes into watery
  fluids on both sides

 Act as emulsifiers in blood --
  keeps lipids (TG,cholesterol)
  suspended
   The Chemist’s View: Sterols
 Ring-shaped, with
  side chains attached
 Popular sterol-
  cholesterol
  – Found in some plant
    products, but mainly
    animal
  – Plant sterols reduce
    blood cholesterol

          Made from Cholesterol
                            Sterols
 Roles of sterols
   – Formation of body compounds
         Vitamins (D)
         Bile
         Hormones (i.e., testosterone, cortisol)
         Cholesterol
   – Cholesterol is found in all cell membranes
       90% of body cholesterol is found in cells
 Sterols are found in foods
   – Manufactured in bodies by liver so non-essential
     (endogenous)
   – Dietary sterols (exogenous) eggs (yolk), fish(moslly
     shell fish), red meat
                   Sterols
 Animal Sterols
  – Significant amounts of cholesterol
  – Meat, eggs, fish, poultry, & dairy products
  – Difference b/w dietary & blood cholesterol


 Plant Sterols
  – Component of plant cell membranes
  – Can interfere with cholesterol absorption (from
    animal cholesterol)
       Functional Food Product
 Becel Proactiv with Plant Sterols
 Ingredients:
   – Water 53%, Canola and Sunflower oils 30%, Plant
     Sterols 9%, Modified Palm and Palm Kernel oils
     2.5%, Salt 1.5%, Gelatin 1.5%, Whey Powder 1%,
     Vegetable Monoglycerides 0.2%, Soy Lecithin
     0.2%, Potassium Sorbate 0.1%, Lactic Acid, Calcium
     Disodium Edta, Natural and Artificial Flavours, Citric
     Acid, Vitamin A Palmitate (Vitamin A), Vitamin D3,
     Alpha Tocopherol Acetate (Vitamin E), Beta-Carotene.
Digestion, Absorption,
and Transport of Lipids
           Digestion of Lipids
 Aim to dismantle triglycerides into small molecules
   – Monoglycerides –can absorb this
   – Fatty acids -may get further broken down
   – Glycerol
 Digestive enzymes are in water solution.
 Fats and water don’t mix.
 How can enzymes come in contact with lipids?
-Mechanical digestion in stomach (churning and
  mixing)
Lipase in stomach will start some breakdown of fat too
          Digestion - 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
           Digestion - 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 still not fully broken down here
  – Helps expose fat to gastric lipase
    enzymes – works primarily on short chain
    fatty acids.
       Digestion – Small Intestine
 Fat enters the SI
   – CCK signals gallbladder to
     release bile
   – pancreas secretes lipase
   – Intestinal lipase

 Enzyme can now come in
  contact with fat as they are
  mixed within the watery
  contents.
Digestion – Chemical Reaction
Hydrolysis of Lipids
 Enzymes break down TG to 1MG and
  2 fatty acids, & sometimes down to
  glycerol and the 3rd FA (3 free fatty
  acids)

 PhospoLipid hydrolyzed similarly


 Cholesterol not digested
  Absorption - Small Intestine
 Glycerol, short & medium chain FAs simple diffusion
 Mionoglycerides & long-chain FAs are arranged as
  lipoproteins for absorption & transport.
  – Micelles: spherical complexes formed by molecules of bile
    surrounding monoglycerides & fatty acids
 Once inside intestinal cells FAs put back
  together into TriGlyceride & packaged into
  lipoproteins.
  – Specific Lipoprotein produced to transport fat are
    called chylomicrons specialized cells on liver to attract
    the chylomicrons
  – Chylomicrons released to lymphatic system
  – Enter blood stream at thoracic duct
Absorption
           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.
             1. 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 dismantle them & use them or recycle
  pieces.
   2. Very-Low-Density Lipoproteins
               (VLDL)
 Made by liver cells to transport lipids to various tissues.
 As they lose TG, become denser. (and then end up with
  the LDL)

   3. Low Density Lipoprotein (LDL)
 Derived from VLDL, ~ ½ cholesterol. (less TG)
 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 bc they deposit
  TG, and have a high actual cholesterol component to
  them
 4. High Density Lipoprotein
                       (HDL)


 Transports cholesterol back to liver from
  cells (scavenger). (main fxn) –acts as a scavenger

 ~ 45-50% protein. Why considered high density.


 Commonly known as “good” cholesterol
         Lipoproteins & Health
 LDL- linked to cardiovascular disease
  – Build-up of cholesterol in blood vessels
  – Pathway: Liver→ Cells/Tissues/Blood vessels
  – Higher levels are linked to higher risk


 HDL- protective effect
  – Removal of extra cholesterol in blood vessels
  – Pathway: Cells/Tissues/Blood vessels→ Liver
  – Protective effect
   3 primary fates of dietary fat
1. Can immediately be taken up and used as a
   source of energy for cells.

2. Can be used to make lipid-containing
   compounds in body. Use to make
   hormones

3. Can be stored in adipose tissue as TG for
   later use.
                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.

 Also, energy used at rest is from fat
                     The Role of Fats
 Fat is essential to many body functions
   – Cell membrane structure
   – Nerve cell transmissions
   – Protection of internal organs (IE: kidneys are
     surrounded by fat, abd fat to protect liver)
   – Insulation to retain body heat

 Fat-soluble vitamins
   – Vitamins A, D, E, and K are soluble in fat; fat is
     required for their transport
   – -dissolve in fat
   – Are essential
             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 give us more energy per gram
  – Fats take longer to digest lengthens amount of
    time for signals to send out saying you are
    hungry again
                   Lipids in the Body
 Adipose Tissue
   – Main energy reserve
   – Actively secretes hormones “adipokines”
      Adipokines regulate energy balance and influence body
      functions e.g. insulin sensitivity
   Altered when body fat is markedly lower or higher

   – High body fat increases release of resistin
     and decreases adiponectin
 Resistin – inflammation and insulin resistance
 Adiponectin – anti-inflammatory : also helps regulate hunger
               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 member Linolenic acid
       Precursor to Eicosapentaenoic acid (EPA) &
        Docosahexaenoic acid (DHA) -EPA & DHA essential to growth
        and development especially brain and eyes. EPA plays role in
        blood clotting, reduce formation of
       Found in vegetables, fish & fish oils
       Omega 3 is anti-inflammatory in nature

   Omega-6 fatty acid family
      Primary member Linoleic acid
       Precursor to: Arachidonic Acid (AA)
       Found in vegetable and nut oils
         Lipids in the Body
 Eicosanoids
  – Arachidonic acid & EPA used to make
    eicosanoids
     Hormonelike - prostaglandins, thromboxanes &
      leukotrienes(don’t need to know the name of these
      hormones)
     EPA ecosanoids ↓ blood pressure, prevent
      blood clot formation, protect against
      irregular heartbeats & ↓ inflammation
     Arachidonic acid ecosanoids less beneficial
              Lipid Metabolism
Storing Fat as Fat - Adipose Tissue (Adipose
 tissue has virtually unlimited capacity)

 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.
             Lipid Metabolism

 Making Fat from CHO or Protein


  – FA can be made from 2 carbon chains
    derived from any energy yielding
    nutrient.
  – If consume too much CHO or protein, it gets stored as fat.
          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
Adipose cell
       Health Effects (of fats)
 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. Depend on type of fat and how
 much
      Cardiovascular Disease
 Risk factors for cardiovascular disease
 include:
  – Being overweight
  – Physical inactivity can be normal body weight
    but if not physically active have risk factor
  – Smoking
  – High blood pressure
  – Diabetes
  – Also genetics (which can’t be altered as the
    above ones can be)
      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)
  – LDL is highest in cholesterol.
                  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
      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
       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

      Eggs are high in cholesterol, but are a good source
       of protein.
CVD - Atherosclerosis
             Cardiovascular Disease
Cross-section of (a) a normal artery and (b) a partially blocked artery.




                                       Lumen is starting to narrow in (b)
          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
    (fortified with omega-3; juices, yogurt)
  – Caution re supplement use
  – Too much – decrease immune system, raise LDL, increase bleeding
    time, interfere with wound healing
      Cardiovascular Disease
 Other ways to raise HDL & lower LDL
  – High fibre diet (including soluble fibre)
  – Weight control
  – Physical activity
  – Moderate alcohol consumption women 1/day;
    men 2/day.
  – Plant sterols & stanols -plant cholesterols
           Mediterranean Diet
 More emphasis on fish, vegetables, fruits
  and grains
  – Lower consumption of red meats
  – Most fat comes from olive oil and nuts mono or
    poly unsaturated fats
 As a result:
  – Less saturated/trans fats
  – High in unsaturated fats, complex carbs and
    antioxidants
  – Lower risk of heart disease, cancer and higher
    life expectancy
                                -Red meat once a month
                                -Eggs, poultry, fish weekly




Mediterranean dietary pyramid
               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 (once you have it, it grows faster)
  – Omega-3 FA may protect against cancer
               Health Effects
 Obesity
  – High fat consumption generally equates to
    excess energy intake
      Especially if inactive and not burning fat you are
       taking in


  – Cutting fat can effectively cut calories
      Watch for what replaces fat in food products IE: in
       fat free cookie...what replaces the taste? –more
       sugar! So you end up getting the same amount if
       energy from it
      Also make sure still getting the good fat
           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. And replace with carbs
            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. –would like to see ppl
    eating none (this is hard to achieve though)
  – Most fat in our diets should be from mono-
    and poly-unsaturated fats.
  – Cholesterol <300 mg/day
            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
      >50 yr males: 14 g/day & females: 11 g/day


 α-linolenic acid
  – AI
      14->50 yr males: 1.6 g/day
      14->50 yr females: 1.1 g/day
  – DON’T NEED TO MEMORIZE THESE!
    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. Go
  for whole grains
 Drink skim, 1% or 2% milk each day.
 Select lower fat milk alternatives. Choose soy beverages low in
  fat
 Have meat alternatives such as beans, lentils & tofu often.
  Replace meat with these
 Eat at least 2 Food Guide Servings of fish each week.
 Select lean meat & alternatives prepared with little or no
  added fat or salt also about type you choose and how you cook it
   – Look for round or loin cuts
   – Grill, roast, broil, bake, stew or braise. BBQ is a good way too

 Include a small amount of unsaturated fat & limit amount of
  saturated & trans fats in diet.
    From Guidelines to Groceries
 Visible fats
  – Fats we knowingly add to foods
  – Butter, cream (in coffee), mayonnaise
    (unsaturated fats), dressings

 Invisible fats
   – Fats hidden in foods –fat marbled in meats
   – Naturally occurring or added during processing
   – i.e. marbled fats in meats, fried & deep-fried
     foods, baked goods
From Guidelines to Groceries

Butter             Margarine
 Rich in SF and    Low in SF but may
  cholesterol        contain TFA
                    No cholesterol
                    Choose carefully
                     – Look for non-
                       hydrogenated soft tub
                       margarines (becel,
                       celeb, etc.)
                     – If hydrogenated it will
                       have Trans fatty acids
                       which are bad!
  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.
   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 150g fish per wk.
      Women who are or may become pregnant and
       breastfeeding mothers can eat up to 150g fish per
       month.
      Children between 5 & 11 yrs of age can eat up to
       125g fish per month. Children between 1 & 4 yrs
       of age should eat no more than 75g fish per
       month.
  From Guidelines to Groceries
Mercury in fish
 Health Canada guidelines
   – For canned albacore (or white) 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.
 most canned tuna is young fish with less mercury
  content
              Fat Replacers
 Made from CHO, protein or fat sources
 Used to replace fats (partially or entirely)
  – May yield some energy (absorbed by the
    body) but not as much as regular fat. (ie:
    dates in a brownie to give same texture)
 Artificial fats- a replacement for fat
  – No energy (not digested)
  – Found in chips and other snacks
  – Most common is olestra
 Olestra
  – Fat-based
      Sucrose molecule replaces glycerol backbone
  – Passes through digestive system
  – Non-toxic, but can impair nutrient absorption
      Removes fat soluble vitamins
  – Can speed GI motility
      Cramping, bloating, loose stools, gas
      In the US- warning label used
      Olestra not used in Canada
      Producer will often add back in
     fat-soluble vitamins to counteract for
     action of removal of them.
      Next
     Chapter 6
Protein: Amino Acids

				
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