Food “combining”
• Some holistic medicine advocates have
suggested that combining fats, proteins and
carbohydrates in a meal prevents proper
digestion of these macronutrients
• What do you think?
Digestion pathways
• Carbohydrates; enzymes in saliva begin the
process
• Proteins: pepsins in stomach initiate
breakdown
• Fats: Lipases excreted in walls of small
intestine and pancreas
• So……………………triage results?
Conclusion
• It is not an issue to combine all 3
macronutrients in a single meal !!
8. Lipids – Fats & Oils
Chapter 15
Lipids
A lipid is an organic substance found in living
systems that is insoluble in water but is
soluble in organic solvents.
Lipids vary widely in their structures. They have
mostly C,H and some have a few polar atoms/
functional groups.
Lipids include:
fats and oils
steroids
waxes
Fats & oils make up 95% of the nutritional lipids,
the other 5% are steroids. Waxes are functional
only.
Fats are solid triglycerides
Oils are liquid triglycerides
Fats and Oils
The Triglycerides We Eat
CH2-O2C-R
HOCH2-CHOH-CH2OH CH-O C-R’
2
(glycerol)
CH2-O2C-R”
Fatty acid side
chains
Triglycerides/fatty acids are characterized/named
by:
1) The length/number of carbons in the side
chains
2) The number of carbon-carbon double bonds in
the side chains(the degree of unsaturation).
Representative Fatty Acids
C12-C18(also C20) Dietary Fats and Oils
CH3-(CH2)12-COOH
CH3-(CH2)14-COOH
CH3-(CH2)16-CO2H
CH3-(CH2)7-CH=CH-(CH2)7-CO2H
CH3-(CH2)4-CH=CH-CH2-CH=CH-(CH2)7-CO2H
CH3-CH2-CH=CH-CH2-CH=CH-CH2-CH=CH-(CH2)7-CO2H
Name
(1)
(2)
(3)
(4)
(5)
(6)
Myristic acid
Palmitic acid
Stearic acid
Oleic acid
Linoleic acid
Linolenic acid
Mp(oC)
58
63
71
4
-5
- 11
(1)
(2)
(3)
(4)
(5)
(6)
Class
Saturated C-14
Saturated C-16
Saturated C-18
Monounsaturated C-18
Polyunsaturated C-18
Polyunsaturated C-18
Fatty Acid Content of some Fats/Oils
Canola (Canadian-oil-low acid)
• Oil from Canadian rapeseed
• Has “ideal ratio” of omega-6 to omega-3
fatty acids of 2:1
• Also very low in saturated fat
Olive oil
• Deemed to be the most “heart healthy”
• Highest % of monounsaturated fatty acids
• Extra virgin (1st press)
Oxidation of Organic Compounds,
eg. fatty acids
O2
-C-C-C-COOH
saturated
-C-COH-C-COOH
difficult
O2
-C=C-C-COOH
-COH-COH-C-COOH
unsaturated
easy
oxidation = decomposition = rancidity
more saturated = more stable, ie. longer ‘shelf life’,
eg. commercial baked goods
more unsaturated = faster deterioration, ie. need
antioxidants to protect compounds(in the body?)
Hydrolyse: to convert (lyse = to cleave) a compound
into other substances through the action of water.
-H2O
R-C=O
O-H HO-R’
acid + alcohol
(fatty acid + glycerol
+H2O
R-C=O
O-R’
ester
triglyceride)
FATTY ACIDS (TRIGLYCERIDES)
Solid: longer chains
saturated(only C-C)
eg. animal fat, butter
Liquid: unsaturations (C=C)
eg. many vegetable oils
(olive, sunflower)
Unsaturates can’t fit well into a solid lattice
Reactions (Metabolic)
O2
Fatty Acid
*
C2 pieces + CO2 +
H 2O + energy
Humans cannot make:
* “Essential” Fatty Acids: Linoleic: 18(9,12)
Linolenic: 18(9,12,15)
Body fat is stored energy
The body converts the unused carbohydrates,
proteins and triglycerides that make up our
macronutrients into small globules of fat that
end up in the specialized cells of adipose
tissue, the fatty tissue of the body.
One pound of adipose tissue stores, and
provides when needed, ~3500 Cal of energy.
The high energy density of fat - its ability
to store energy (9 Cal/gram) compactly in
relatively little space and with relatively little
weight, compared with carbohydrates and
proteins (4 Cal/gram), allows us to carry
stores of energy with us.
It give humans and other animals the
mobility and freedom necessary for survival
Water in the Camel’s Hump
C54H108O6 + 78O2
54CO2 + 54H2O + zillion Cal
(triglyceride from C18H36O2 x 3 ie glycerol tristearate)
Metabolism requires oxygen, produces energy, carbon
dioxide and water
Fat = Essential Energy
Most of our long term energy supplies operates
via the formation, storage and metabolism of
body fat (triglycerides).
Short term energy storage, from one meal to
another, occurs through a starch-like substance
called glycogen(a carbohydrate).
Adipose Tissue / Fat
Adipose tissue forms cushioning shields around our
major organs, protecting them against damage from
physical shock and provides insulation to our
bodies, guarding against a rapid loss of body heat to
the external environment .
Fats carry the flavours and vitamins of many of
our foods although fats have no flavours of their
own, eg. carrying vitamins A, D, E and K from
our foods to our tissues.
Fatty acids form not only the triglycerides but other
compounds as well, including such vital classes as
prostaglandins and phospholipids.
Reactions (“Synthetic”)
Iodine # ( sat. unsat.)
I
C C
I I
C C
C C
I
C C
Iodination
H H
C C
H
C C
H
Hydrogenation
unsaturated
saturated
Saponification/Hydrolysis of a Triglyceride
O
O
CH2 O
CH2 OH +
R
R
O
O
CH O
R'
3NaOH / H2O
CH OH + R'
Heat
O
CH2 O
O Na
+
R''
triglyceride
O Na
+
O
CH2 OH + R''
glycerol
O Na
soaps
+
Omega - 3 Fatty Acids - Especially in Fish Oils !
Mainly 20 & 22 C’s, polyunsaturated and
1st ‘ene’ is 3 from -end.
Eicosapentaenoic acid (EPA): 20(5,8,11,14,17)
mp –50OC !
Docosahexaenoic acid (DHA): 22(5,8,11,14,17, 20)
 - alpha end
COOH
 - omega end
also -linolenic: 18(9,12,15)
Why ‘Omega – 3’ FA ?
Low incidence of heart disease amongst
populations that eat lots of fat BUT mostly as fish !
eg. Inuit & Greenlanders
Sat Mono Poly(16 &18)
Cod
Herring
15
20
29
5
Don’t like fish?
-3(20 &22)
20
21
Try omega 3 eggs!
35
53
Omega-3 eggs
• Chickens are fed flaxseed, which contains
high levels of omega-3 fatty acids. After 10
days, this modifies the fat content in the
egg yolk to contain more omega-3 fatty
acids and less saturated and omega-6’s
• In 1997, this was the Canadian New
Product of the year
Omega-3 Chickens
Omega-3 meats
• Present work (Guelph) on chickens,
turkeys, pigs to obtain meat with high
omega-3 fat content via diet alterations
• Coming soon to a supermarket near you!
Other omega -3 enriched
products
• Orange juice
• Other fruit juices
Cis vs. Trans Fatty acids
• Almost all natural unsaturated fatty acids
have cis stereochemistry in C=C’s.
• Small amounts of trans are produced in
stomachs of ruminating animals by partial
enzymatic hydrogenation of
polyunsaturated fats, and thus are present in
small amounts in milk and butter
Commercial Hydrogenation of Fatty Acids
H
H
C C
R
H H
partial H2 catalyst
H
R C C R +
R
‘cis’
unsaturated
natural
good
H H
saturated
natural
bad
R
C C
R
H
‘trans’
unsaturated
unnatural
bad
An unwanted byproduct
• Trans fats increase the level of Low density
lipoprotein (LDL).
• Thus they are deemed to be “heart
unhealthy” since LDL tends to deposit
cholesterol in the arteries rather than
transport it (as does HDL) to cells for use
in cell membrane construction.
How are trans fats metabolized?
• Catabolism (breakdown) of all fats
• Catalyzed by lipases to free FA’s and
glycerol
• FA’s split by beta oxidation into 2C units
(Acetyl Co), or propionyl CoA if odd #C’s
• Need bile salts to emulsify fats and allow
absorption by the intestine (occurs 1st)
Also have anabolism
• Macromolecules (ie Proteins) synthesized
using 2C units derived from fat
metabolism, amino acids etc
• Essential link between energy producing
(catabolic) and energy utilizing (anabolic)
pathways is ATP (adenosine triphosphate)
• Details much beyond the scope of this
course!!
‘Trans’ = Saturated; in shape and ‘badness’ !
Incomplete Labels !
‘Trans Fats’ - Misleading Labels
‘Trans Fats’ – an Informative Label
Cholesterol - a
steroidal alcohol
(atherosclerosis!)
H3C
CH3
CH3
CH3
H3C
HO
Cholesterol (animal "fat")
High – red meat, egg yolks, dairy products
Low – egg whites, yoghurt
None ! – fruits, veggies, vegetable oils
Properties of Cholesterol
very insoluble in water, C27H46O
solid, mp. 149o
compact, stiff/rigid
Cholesterol is Absolutely Essential !
The average male (80kg/170lb) contains ~220gm
About:
50% in cell membranes
40% converted to bile
acids to ‘emulsify/
transport’ lipids (liver>
gall bladder> intestines)
some converted to
hormones (testosterone,
estrogens, cortisone)
in 80kg male (~gms)
blood 16
muscle 45
brain 50
adipose tissue 45
skin 18
liver 8
heart/kidney, etc. 8
adrenal glands 2
alimentary tract 7
Cell Membrane Structure (lipid bilayer)
Cholesterol Transport in vivo
• Cholesterol is insoluble in water, hence to
transport it through the bloodstream, our bodies
wrap it in a sheath of proteins and varying
amounts of triglycerides to form lipoproteins.
• High Density Lipoproteins (HDL’s) transport
excess cholesterol to the liver for disposal “good
cholesterol”
• LDL’s (Low Density Lipoproteins) and VLDL’s
tend to deposit cholesterol on arterial walls “bad
cholesterol”
Structural features: HDL vs LDL
• HDL contains unsaturated cis Fatty acids
• LDL contains more saturated and trans
fatty acids
• Both contain apolipoproteins and
phospholipids which are oriented with
hydrophobic part on inside and outer
hydrophilic edges exposed
Cholesterol in gallstones
• Bile : used in fat digestion
• Contains water, cholesterol, bile salts , proteins
and bilirubin (waste product)
• If bile contains too much cholesterol, it can
harden into gallstones
• Extraction of cholesterol from gallstones
(removed by surgery) is a common lab
experiment!
• Size can range from grains of sand up to golf
ball!
Source of bile acid
•
•
•
•
Produced in liver
Stored and concentrated in the gallbladder
Secreted into small intestine
If gallstone blocks exit duct, then
gallbladder may need to be removed
• Fat digestion becomes more difficult, but
not impossible
Gallstones
Some real ones!!
• Courtesy of the Ottawa Hospital!
Some Risk factors for gallstones
• Gender: Women 2x as likely; excess estrogen
from pregnancy, BC pills, HRT all may increase
cholesterol levels
• Weight: even moderate obesity
• Diet: high fat, low fibre diet increases level of
cholesterol in bile
• Rapid weight loss: crash diets as body tries to
metabolize fat
• Age.>60: body secretes more cholesterol into bile
Lipid Content (mg) per serving
of common foods
• Includes cholesterol
• Saturated fatty acids
• Unsaturated fatty acids
Fat and Oil Content
Food
Cholesterol Saturated Monounsaturated Polyunsaturated
Beef
91
2.7
2.7
0.5
Butter
219
50.5
23.4
3
Cheese ,cheddar
105
21.1
9.4
0.9
Cheese , cottage dry
7
0.3
0.1
0.02
Chicken (no skin)
85
1.3
1.5
1
Corn oil
0
12.7
24.2
58.7
Eggs , whole
548
3.4
4.5
1.4
Frankfurter (all beef)
51
12.7
14.8
1.2
Margarine,stick(coin oil )
0
13.2
45.8
18
Milk , skim
2
0.1
0.05
0.007
Milk whole
14
2.3
1.1
0.1
Olive oil
0
13.5
73.7
8.4
Peanut butter
0
9.7
23.3
15.2
Peanut oil
0
16.9
46.2
32
Safflower oil
0
9.1
12.1
74.5
Salmon (pink , canned)
35
1
1.8
2.7
Tuna (canned in water )
63
0.2
0.1
0.2
Turkey (no skin )
69
1
0.6
0.9
Yogurt (plain , lowfat)
6
1
0.4
0.04
Note
• No cholesterol in products derived from
plant sources!!
Canada (Cholesterol, mmol/L)
Risk Level
Total
LDL
HDL
Low
<4.5
<3.5
1.2
Border-line
5.0-6.0
4.0
1.0
High
>6.0
>4.5
0.9
Total / HDL should be 4.0 or less
USA (Cholesterol, mg/dL)
Risk Level
Total
LDL
HDL
Low
<200
<130
50
200-239
130-159
>240
>160
Border-line
High
35
Cholesterol Related compounds
• 7-dehydrocholesterol (functions as a
cholesterol precursor in blood serum) gets
converted in vivo (epidermal cells) to
Vitamin D by the action of sunlight
Are you getting enough Vitamin D?
• Deficiency leads to poor teeth and bone
development (rickets) in children
• Vitamin D is added to milk to offset lack of
sunlight in winter ; aids in Ca absorption
• Darker skin prevents UV action
• Some MS connection (2009)-all people
should be taking supplements of it.
Can one get too much Vitamin D?
• Yes-overuse of Vitamin D supplements can
lead to excessive absorption of Calcium
and formation of Ca deposits in kidneys
• Exposure to sunlight is not a problem;
Melanin formation (tanning) stops the UV
induced reaction
• Recent claims re: Cancer retardation are
controversial
Conclusions?
• Drink your milk (and less carbonated
sodas)
• Take cod liver supplements if no exposure
to sunlight
• Some exposure to sunlight is good (~1 hour
per day)
• Avoid mega doses of any fat soluble
vitamin
Phospholipids
Phospholipids
nonpolar tails
(HC)
‘-’ or R
a phosphatidic acid
polar head
(charged)
Phospholipid Bilayer = Cell Membrane/Wall
-water outside cell-
hydrophilic surface
hydrophobic
interior of cell
wall
-water inside cell-
Phosphoglyceride Aggregate = Cell Wall
-cell exterior-
-cell interior-
Lecithin - Another Phospholipid
(emulsifying agent in egg yolks for mayonnaise,
candy, cake dough)
Egg yolks
• Yolk; weighs~20 grams; 33% of weight of total
egg liquid
• 50% water, 16% protein, 34% lipid
• ~6.8 x9 =61.2 Cal from fat; 3.2 x4=12.8 Cal from
protein
• Total ~74 Cal. vs. 15 Cal in egg white
• Functions as stored food for the embryo
• Supermarket eggs do not contain an ovum, since
they have not been fertilized (no rooster!)
Egg structure
Lipids in Egg yolk
• ~ 66% fat, 30% phospholipid (lecithin),
4% cholesterol
• Lecithin (~2 grams per yolk) acts as an
emulsifier to “solubilize’’ the fat in the
water of the yolk
• Egg yolks used commercially to produce
mayonnaise, an emulsion
Origin of Phospholipids
• Biosynthesized in humans from
glycerophosphate and Fatty acid CoA
• ATP (adenosinetriphosphate) is needed as
a phosphorylating agent
Emulsifying power of an egg yolk
• 2 grams per yolk of lecithin (MW~800)
• # of moles =2/800= 1/400
• # of molecules=1/400 x Avogadro’s
number
• 1/400 x 6.02 x 1023~ 1.5 x1021 molecules!
Surface Area
• Consider a layer of lecithin one molecule
thick on the surface of water
• The polar head of one lecithin molecule
takes up about 1.6 x 10-15 square inches
• Thus the total surface area of oil protected
by lecithin=1.6 x10-15 x 1.5x1021 sq inches
• Or 2.4 million square inches
How big is a football field (US)
• 100 yards x 50 yards= 5000 square yards
• In a square yard there are 36 x 36 =1296
square inches
• Thus in 2.4 million square inches, there are
2,400,000 /1296= 1851 square yards (or
about 1/3 of a football field)
So………….
• The surface area of oil protected by the
lecithin in an egg yolk covers over 1/3 of a
football field
• Hence huge emulsifying power
• Ref. “The Curious Cook” by Harold
McGee, McMillan 1990
Salmonella Enteritidis (SE bacteria)
• From fecal matter ; egg comes out by same path as
fecies; eggs are washed and sanitized before sale
• Can get into yolk or white, before the shell is formed if
the hen’s ovaduct or ovaries have been contaminated
• Raw eggs should not be consumed
• SE causes severe abdominal pain, nausea in humans,
particularly if taking antacids
• SE can be destroyed by acid, antibiotics
• Not fatal but can cause ~2 weeks of discomfort!
Commercial mayonnaise
• Made with Pasteurized eggs to avoid SE
• Heat at 55-70oC kills bacteria
Soy Lecithin: comes from soybean oil
Lecithin in Chocolate
• Acts as surfactant (0.5 to 1%) to aid in the flow
of liquid chocolate
• Polar end surrounds sugars ( OH groups)
• Non polar end interacts with fat
• Hershey Plant (Smiths Falls) closing 2006 due to
Salmonella in soy lecithin (Dec 2/06 reopening)then permanent closure in 2007.
• Salmonella bacteria (normally from undercooked
poultry) enter small intestine causing infection
How can Salmonella get into soy
Lecithin products?
• Soybeans are often left to dry on open
ground, hence are subject to soil fecal
contaminant unless sterilized (roasted)
Waxes = (large mol.wt.) Esters (R-COOR’)
Birds/insects - water repellant feathers/exoskeletons
Leaves/fruit - minimize water evaporation
Humans - to plug up ears!
beeswax; R= C15, R’= C30;
carnauba wax(Brazilian palm): R= C31, R’= C34
*spermaceti(whales): R= C15, R’= C16(mp.31oC)
Whales have 4 tons*(in head). While swimming on
surface(37oC) it is a liquid. When they dive (1000m) to
feed, the oil solidifies, increases in density, and whale
can stay submerged without effort until ready to return
to surface where oil remelts for buoyancy.
Density of solids vs. liquids
• Behavior of whale oil is normal-ie liquid is
less dense than the solid
• Water is the only substance on the planet in
which the solid (ice) is less dense than the
liquid
• Water at 4oC is the most dense!
Soaps/Detergents
Chp.13
Contain a nonpolar fat component (tail) and a
polar head
Bipolar Behaviour of Soaps, etc.
CH3(CH2)8
SO3- Na+
alkylbenzene sufonate(anionic)
Detergents =
Synthetic Soaps
ie. hydrocarbon tail +
polar/charged head
CH3(CH2)13OSO3– Na+
alkyl sulfate(anionic)
CH3(CH2)8O(CH2CH2O)nH
(nonionic)
CH3(CH2)11N+(CH3)Cl –
trimethylalkylammonium(cationic)
A Typical Soap Molecule
hydrophyllic
hydrophobic
‘loves’ H2O
‘hates’ H2O
Soap makes Grease ‘water-soluble’
Soaps in Hard water
• Curd formation due to insoluble Fe, Ca and
Mg carboxylates
• Water softeners: exchange Na for Fe, Ca
and Mg ions, increasing solubility of the
carboxylates
• Detergents function better in hard water
because sulfonates are soluble
Problem Set #3
• Chapt 15 # 1,8,9,10,11,25,29
• Chapt 13#1
• Chapt 16 #1,9,11,12,18