Download lipids - U of L Class Index

LIPIDS
Groups of Lipids
• Triglycerides
– major lipids
– fats and oils
• Phospholipids
– membranes
• Sterols
– steroids
– hormones
– cholesterol, bile
Function of Fat
• Protection against
– temperature (insulator)
– mechanical shock (bumper pad)
• Structure and health of cells
• Continuous supply of energy (fuel)
– ex. Polar bear, person fasting
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Brain cells need glucose for energy
some glucose can be supplied by amino acids
extended fast---------> lose muscle
without glucose, fat breaks down into ketones
ketones supply approx. 1/2 the energy need of the brain and CNS
Still need glucose
Function of Fat in Food
• Carries the fat soluble vitamins (A,D,E &K)
– mobilizes and stablilizes the vitamins
– high temperature can destroy fat soluble vitamins (floats on top)
– skim milk loses Vit. A $ D ---> fat removed
• (fortified)
• Adds palatibility to food
– aroma, flavour
• Add kCal
Fatty acids
• Basic unit of fats
• Can be saturated or unsaturated
• Comprise triglycerides
Saturated Fatty Acids
• Fatty acids containing no double bonds
• The carbons are fully loaded with hydrogens
– like a sponge soaking up water
Unsaturated Fatty Acids
• Hydrogens are missing
• As a result double bonds have to form between the carbon atoms
so that each carbon atom has 4 bonds
• These are called carbon-carbon double bonds
– omega-3 (a-linolenic - major)
– omega-6 (linoleic)
Ketosis (ketone bodies)
• Results from the incomplete oxidation of fats
• lack of CHO in cells during diabetes can result in keton body
buildup - toxic levels - ketosis
• fasting - body finds a way to fuel the brain
• ketone bodies are part of normal metablolism
• brain need glucose or 6C units
Triglycerides (Triacylglycerides)
• Consist of a glycerol backbone (alcohol) esterified with acyl
groups
• Structure of the fat stored in our body and oil stored in seeds
• Triglycerides are mixtures of different alkyl side groups
How much fat should we eat???
• No RDA/RNI for fatty acids
• current Canadian recommendation is a minimum of 3% of fatty
acids should come from Omega-6 FA (linoleic) and 0.5% should
come from Omega-3 fatty acids
• ratio of 4:1 - 10:1
• total fat in diet should be divided equally between saturated,
polyunsaturated and monounsaturated fats
• cholesterol should be no more than 300 mg per day
Essential Fatty Acids
• Essential Nutrient - one the body can’t make in sufficient
quantitiy to meet physiological needs
• Omega-6 fatty acids
• Linoleic (18:2) - plants, oils
– precursor for arachidonic acid
• Arachidonic Acid (20:4) - meat
– extremely important in membranes
– deficiency - skin reddening, prone to infection, dehydration, liver
abnormalities, growth failure
• We don’t have the enzymes to put a double bond in at the (18:2)
arrangement
• The body can make (20:4) arachidonic acid from linoleic (18:2)
but very, very slowly
• Therefore it is a good idea to eat both vegetable oil and meat
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Omega-3 Fatty Acids
Linolenic (18:3) - essential
Linolenic------>EPA (20:5) and DHA (22:6)
EPA - eicosapentanoic acid}- omega-3
DHA - docosahexanoic acid
both come from fish oil and seafood
both have an important role in vision and neurological function
• Cannot make Omega-6 fatty acids from Omega-3
• Therefore both are essential in the diet
• Optimum: 1 gram of Omega-3 FA fro ever 4-10g of Omega-6
FA
• Fish is very important in the diet
Further Benefits of Fish Oils
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Linoleic--->Arachidonic--->Thromboxane
Thromboxane - prostaglandin - promotes clotting
EPA and DHA both displace thromboxane
High EPA/DHA--->low Thromboxane--->decreased clotting--->decreased complications of heart disease (decreased heart
attack risk)
• EAT FISH
Stability of fatty acid and the processing of food
• Fish oil unstable - unsaturation
• more double bonds--->more easily oxygen can destroy the fatty
acid (oxidation)
• Fatty acid--->Oxygen--->Rancidity
• Unsaturation---> Liquid (RT)
• Saturation---> Solid (RT)
• In general, unsaturated fatty acids are less stable than saturated
fatty acids
Dealing with Spoilage
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Refrigerate (expensive)
Seal sontainer tightly (reduce exposure to O2)
Add preservatives and antioxidants (Vit C., DHA)
Hydrogenation - reduces the # of double bonds (by adding H2 to the
double bond)
– makes fat more solid (less labile)
– decreases unsaturation
– decreases HEALTH VALUE
Partial Hydrogenation
• In partial hydrogenation, not all the double bonds are broken,
and rearrangement from cis to trans occurs
• We are capable fo rbreaking down cis FA
• Problems are associated with breakdown of trans FA (metabolism
of these is not well understood
• Linked to Cancer
Digestion of Fat
• Fat soluble cmpds are “Water Fearing” (Hydrophobic) (Non
polar)
• Hydrophilic - “Water Loving” (Polar)
• Water tends to push hydrophobic molecules together (ex. Oil
forming a layer on top of salad dressing)
• To digest fat we must first mix it with water
• Help from compounds that are both hydrophilic and hydrophobic
in the same molecule
Emulsifiers
• Work to solubilize fat
• Act as detergents (ex. Lecithin in eggs helps to keep Ceasar
Salad from separating - creamy)
• Has a hydrophobic tail and hydrophilic head
• In our bodies we have;
– bile salts
– phospholipids
• Serve to disperse and stabilize small fat droplets in water
solutions
Phospholipids
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Important component of cell membranes
Emulsifying agents (dispersion of fat)
Part lipoprotein structures
Emulsifiers in foods
Bile Salts
• Made from cholesterol in the liver
• Stored in the gall bladder
• Released into the small intestine when fat arrives from the
stomach
Lipase Action
Micelle Formation
• Monoglycerides, fatty acids and bile salts form tine spherical
matrices called micelles
• Fatty Acid micelles have approx. 20 FA/micelle
• Micelles dissolve in the intestinal wall
• Monoglycerides and FA in the micelles are converted to
triacylglycerol and incorporated into Chylomicrons for
transportion
Chylomicrons
• Are lipoproteins (supramolecular complexes which deliver
lipids)
• Contain triacylglycerol
• Transported in the lymphatic system and enter the blood close to
the heart via the thoracic duct
• Short and medium chain FA can be absorbed directly into the
blood
Sterols
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Arranged in rings
contain C, H and O with various side chains
ex. Cholesterol
Many molecules are similar to cholesterol
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bile salts
sex hormone
cortisone
vitamin D
Fate of cholesterol in the Body
Fat Breakdown
• Fat is broken down by a number of compounds in the body to
make it transportable
• Bile Salts
– natural emulsifier
– synthesized in the liver from cholesterol and stored in the gallbladder
Lipases
• Lingual
– initiates fat breakdown
– splits off certain fatty acids
– short-lived
• Gastric
– limited effects
– produced by glands of the stomach wall
– get cleavage of some triglycerides to monoglycerides and diglycerides
• Pancreatic
– secreted along with bile
• Intestinal
– secreted from glands in the intestinal wall
• Pancreatic and intestinal account for the majority of fat digestion
• End products
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glycerol
phospholipids
cholesterol
free fat
monoglycerides
Absorption of Fat
• Short and medium length fatty acids and glycerol are absorbed
through cells lining the small intestine and become attached to
protein carriers
• protein carriers make them water soluble so they can be
absorbed directly into the blood
• Long chain fatty acids, monoglycerides phospholipids and
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cholesterol
Combined into micelles on the surface lining the small intestine
Micelles dissolve into the lining of the intestinal wall thus
bringing the fat with them
Once inside, micelles are repackaged into chylomicrons
Chylomicrons are absorbed by the lymph rather than the blood
Enter the blood via the thoracic duct
Lipid Transport
• Lipids are transported throughout the body by special proteins
called lipoproteins
• Lipoproteins are important in transporting protein from the small
intestine to be broken down and metabolized and for
tranportation of newly synthesized lipids from the liver
• the liver is the major lipid producing organ
• Chylomicrons
• Least dense
• Responsible for transporting most of the end products of fat
digestion
• Monoglycerides and long chain FA combine with cholesterol,
phospholipids and small amounts of protein to form
chylomicrons
• Originate in the cells of the intestine
• Start out housing fat and decrease in size as the circulate
• Fat becomes picked up by the body’s cells
• protein remnant is picked up by the liver and reused
• Very Low Density Lipoproteins (VLDL) (IDL)
• slightly more dense than chylomicrons
• circulate and deliver fat or triglycerides made in the liver to the
body’s cells
• large percent is cholesterol
• contain lipoprotein lipase to break down triglycerides so that
cells can use the fatty acids (delivered)
• become LDL’s when they have transferred their contents (about
2/3)
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Low Density Lipoproteins (LDL)
body’s cells have no means of breaking down cholesterol
therefore it must be returned to the liver to be broken down.
highest proportion of cholesterol
binds to a prtein on the cell membrane (LDL) receptor to all the LDL to
enter cells and deliver the cholesterol
leads to Atherosclerosis
derived from VLDL in the liver
implicated in Heart Disease
“BAD CHOLESTEROL”
• High Density Lipoproteins (HDL)
• Involved in transporting peripheral cholesterol back to the liver
for use or excretion
• “protective” - temporary storage site
• most dense of the lipoproteins
• GOOD CHOLESTEROL
• Idea is to increase the ratio of HDL to LDL
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serum HDL - 60 mg/100 mL (excellent)
Males (30-40)
Females (50-60)
<35 mg/100 mL is a risk of premature heart disease
Atherosclerosis
• Leading form of heart disease
• “Hardening of the Arteries”
• Results from a buildup of cholesterol containing plaque on the
walls of the arteries
• Plaque mixes with protein and becomes covered by a layer of
muscles cells and calcium
• affects funtionality and elasticity
Storage and Release of Fat