Composition and metabolism of lipids

1. 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?

2. 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?

3. Conclusion
• It is not an issue to combine all 3 macronutrients in
a single meal !!

4. COMPOSITION AND
METABOLISM OF LIPIDS

5. 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.

10. Fats and Oils
The Triglycerides We Eat
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).
CH2-O2C-R
CH2-O2C-R”
CH-O2C-R’ Fatty acid side
chains
HOCH2-CHOH-CH2OH
(glycerol)

12. 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
(1)
(2)
(3)
(4)
(5)
(6)
(1) Myristic acid 58 Saturated C-14
(2) Palmitic acid 63 Saturated C-16
(3) Stearic acid 71 Saturated C-18
(4) Oleic acid 4 Monounsaturated C-18
(5) Linoleic acid - 5 Polyunsaturated C-18
(6) Linolenic acid - 11 Polyunsaturated C-18
Name Class
Mp(oC)

13. Structures of Fatty Acids
C
HO
O
C
HO
O
C
HO
O
C
HO
O
C
HO
O
16:0 (palmitic)
cis-18:1 -6 (oleic)
trans-18:1 -6 (elaidic)
18:2 -6 (linoleic)
18:3 -3
(alpha
linolenic)
C
HO
O 20:5 -3 (EPA)

14. Name # Carbons: (saturation)
Palmitate 16:0
Stearate 18:0
Palmitoleate 16:1 - cis at C9
Oleate 18:1 - cis at C9
Linoleate 18:2 - cis at C9 and C12
Linolenate 18:3 - cis at C9, C12 & C15
Important fatty acids:

15. Fatty Acid Content of some Fats/Oils

16. 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

17. Olive oil
• Deemed to be the most “heart healthy”
• Highest % of monounsaturated fatty acids

18. O2
-C=C-C-COOH -COH-COH-C-COOH
unsaturated easy
Oxidation of Organic Compounds,
eg. fatty acids
O2
-C-C-C-COOH -C-COH-C-COOH
saturated difficult
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?)

19. Hydrolyse: to convert (lyse = to cleave) a compound
into other substances through the action of water.
-H2O
R-C=O R-C=O
O-H HO-R’ +H2O O-R’
acid + alcohol ester
(fatty acid + glycerol triglyceride)

20. FATTY ACIDS (TRIGLYCERIDES)
Solid: longer chains
saturated(only C-C)
eg. animal fat, butter
Liquid: unsaturations (C=C)
eg. many vegetable oils
(olive, sunflower)

21. Unsaturates can’t fit well into a solid lattice

22. Reactions (Metabolic)
O2
*
Fatty Acid
C2 pieces + CO2 +
H2O + energy
Humans cannot make:
* “Essential” Fatty Acids: Linoleic: 18(9,12)
Linolenic: 18(9,12,15)

23. 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.

24. 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

25. 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

26. 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).

27. 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.

28. Reactions (“Synthetic”)
Iodine # ( sat. unsat.)
C C C C
I I
H H
C C C C
I
I
C C C C
H H
Iodination
Hydrogenation
unsaturated saturated

29. CH2
O R
O
CH
CH2
O
O
R'
O
O
R''
CH2
OH
CH
CH2
OH
OH
R
O
O Na
+
Na
+
Na
+
R'
O
O
R''
O
O
3NaOH / H2O
Heat
+
+
+
Saponification/Hydrolysis of a Triglyceride
triglyceride glycerol soaps

30. COOH
 - alpha end
 - omega end
Omega - 3 Fatty Acids - Especially in Fish Oils !
Eicosapentaenoic acid (EPA): 20(5,8,11,14,17)
mp –50OC !
Docosahexaenoic acid (DHA): 22(5,8,11,14,17, 20)
also -linolenic: 18(9,12,15)
Mainly 20 & 22 C’s, polyunsaturated and
1st ‘ene’ is 3 from -end.

31. 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) -3(20 &22)
Cod 15 29 20 35
Herring 20 5 21 53
Don’t like fish? Try omega 3 eggs!

32. 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

33. Omega-3 Chickens

34. 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!

35. Other omega -3 enriched
products
• Orange juice
• Other fruit juices

36. 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

37. C C
R
H
H
R
partial H2 catalyst
C C
H
R
H
R
C C R
H
H
R
H
H
+
Commercial Hydrogenation of Fatty Acids
‘cis’ ‘trans’
unsaturated saturated unsaturated
natural natural artificial
good bad bad

38. 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.

39. 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)

40. 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!!

41. ‘Trans’ = Saturated; in shape and ‘badness’ !

42. Incomplete Labels !

43. ‘Trans Fats’ - Misleading Labels

44. ‘Trans Fats’ – an Informative Label

45. Phospholipids
a phosphatidic acid
‘-’ or R polar head
(charged)
nonpolar tails
(HC
)

46. Phospholipid Bilayer = Cell Membrane/Wall
hydrophilic surface
hydrophobic
interior of cell
wall
-water outside cell-
-water inside cell-

47. Phosphoglyceride Aggregate = Cell Wall
-cell interior-
-cell exterior-

48. Lecithin - Another Phospholipid
(emulsifying agent in egg yolks for mayonnaise,
candy, cake dough)

49. 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!)

50. Egg structure

51. 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

52. Origin of Phospholipids
• Biosynthesized in humans from
glycerophosphate and Fatty acid CoA
• ATP (adenosinetriphosphate) is needed as a
phosphorylating agent

53. 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!

54. 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

55. 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)

59. CH3
CH3
O
H
C
H3
CH3
C
H3
Cholesterol (animal "fat")
Cholesterol - a
steroidal alcohol
(atherosclerosis!)
High – red meat, egg yolks, dairy products
Low – egg whites, yoghurt
None ! – fruits, veggies, vegetable oils

60. Properties of Cholesterol
very insoluble in water, C27H46O
solid, mp. 149o
compact, stiff/rigid

61. 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

62. Cell Membrane Structure (lipid bilayer)

63. 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”

64. 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

65. 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!

66. 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

67. Gallstones

68. 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

69. Lipid Content (mg) per serving
of common foods
• Includes cholesterol
• Saturated fatty acids
• Unsaturated fatty acids

70. 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

71. Note
• No cholesterol in products derived from
plant sources!!

72. 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

74. 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.

75. 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

76. 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