Lipids

1
Lipids

• Readings Chapter 5

2
What are Lipids?

• organic compounds that dissolve readily in
  organic solvents but poorly in aqueous solutions
• hydrophobic water fearing
• lipophilic fat loving
• three main classes of lipids
• triglycerides
• phospholipids
• sterols

3
Fatty Acids Building Blocks of Lipids

• fatty acids are molecules composed of a chain of
  carbon and hydrogen molecules with a methyl group
  at one end and an acid group at the other end

ACID group alpha end
METHYL group omega end
4
Classification of Fatty Acids

• Fatty acids are classified based on
• - LENGTH of the carbon chain
• - degree of SATURATION
• - location of DOUBLE BONDS
• - ISOMERIC forms

5
Classification of Fatty Acids

• a) Length
• the of carbon molecules in the chain
• can be 4 - 24 carbons long
• most common in food are 18 carbon fatty acids
• short chain fatty acids are more liquid and are
  more soluble in water

6
Classification of Fatty Acids cont.

• b) Degree of Saturation
• refers to the of hydrogen atoms (H) bound to
  the carbon atoms
• double bonds reduce the of H making a fatty
  acid LESS SATURATED
• refer to as
• SATURATED
• MONOUNSATURATED
• POLYUNSATURATED
• foods contain a mixture of fatty acids

7
Saturated Fatty Acids

• no double bonds between carbon atoms
• solid at room temperature
• example stearic acid
• common sources animal fats (butter, lard, beef
  tallow, etc), cocoa butter, palm oil, coconut
  oil

8
Monounsaturated Fatty Acids (MUFA)

• have a single double bond
• liquid at room temperature
• examples oleic acid
• common sources olive oil, canola oil, peanut oil

9
Polyunsaturated Fatty Acids (PUFA)

• two or more double bonds
• liquid at room temperature
• examples a-linolenic acid linoleic acid
• essential nutrients
• common sources flax seed oil, safflower oil, soy
  bean oil, cottonseed oil, fish

10
Classification of Fatty Acids cont.

• c) Location of Double Bonds
• measured from the methyl end (also called the
  omega end, abbreviated w) to the first double
  bond

double bond
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
O
1
2
HCCCCCCCCCCCCCCCCCCOH
3
H
H
H
H
H
H
H
H
H
H
H
omega 3 fatty acid
methyl end
11
Classification of Fatty Acids cont.

• c) Location of Double Bonds cont.

12
Classification of Fatty Acids cont.

• d) Isomeric Forms
• molecules that have the same atoms but have
  different geometric or positional arrangements

13
Non-Essential Essential Fatty Acids

• the body is able to synthesize most fatty acids
  as needed
• desaturation e.g. removes H from stearic acid
  to make oleic acid
• elongation e.g. adds carbons to build storage
  and structural fats
• the body cannot make fatty acids that have double
  bonds before the 9th carbon
• omega 3 omega 6 must be provided in the diet
  ESSENTIAL FATTY ACIDS

14
Essential Fatty Acids

• Omega 3 Fatty Acids
• polyunsaturated fatty acids with 1st double bond
  three carbons from the methyl end
• Examples linolenic acid, EPA, DHA
• Sources canola, soybean, flaxseed oil, walnut
  oils, fatty fish (tuna, salmon, sardines, etc..)

15
Omega 3 Fatty Acids in Selected Foods
16
Essential Fatty Acids

• Omega 6 Fatty Acids
• polyunsaturated fatty acids with 1st double bond
  six carbons from the methyl end
• Examples linoleic acid, arachidonic acid
• Sources sunflower, corn, peanut, cottonseed,
  soybean oils

17
Functions of the Essential Fatty Acids

• most fatty acids used to provide energy
• small proportion used to make eicosanoids
• Examples
• thromboxanes
• prostaglandins
• leukotrienes

18
Functions of Eicosanoids

• If derived from w-3 fatty acids
• vasodilation
• inhibition of blood clotting
• reduce inflammation
• lower blood cholesterol
• If derived from w-6 fatty acids
• vasoconstriction
• promote blood clotting
• promote inflammation

19
Classes of Lipids Triglycerides

• most abundant form of lipid both in our DIET and
  in our BODY
• formed from 3 FATTY ACIDS attached to a GLYCEROL
  backbone

Fatty Acids
Glycerol
20
Formation of Triglycerides

• occurs via a condensation reaction, produces
  ester bonds

21
Triglyceride Composition

• most triglycerides contain a mixture of more than
  one type of fatty acids, such that they may
  contain saturated, MUFA, and PUFA

22
Functions of Triglycerides

• a) energy source
• in normal conditions supplies 60 of energy needs
  during rest
• preferred fuel of heart, resting muscles
• b) Satiety value - provides satisfaction from
  meal
• c) energy reserve
• stored in adipocytes to provide energy during
  times of energy deficit
• 1 g of fat stores provides gt 6x as much energy as
  1 g of glycogen!

23
Functions of Triglycerides cont.

• d) insulation protection
• visceral fat cushions shields organs
• subcutaneous fat protects insulates the body
• e) transport of fat soluble vitamins
• Vitamins A, D, E, K, carotenoids, other
  phytochemicals
• f) sensory qualities
• contributes to the flavour,
• texture, odour of food

24
Classes of Lipids Phospholipids

• formed from a backbone of glycerol with 2 fatty
  acids, a phosphate, and a nitrogen containing
  group (e.g. choline)
• synthesized in body by the liver
• soluble in both water and lipids

25
Functions of Phospholipids

• a) form cell membranes
• b) lipid transport
• form surface of lipid transport molecules called
  lipoproteins, allowing lipids to dissolve in the
  blood

26
Functions of Phospholipids cont.

• c) emulsifiers
• facilitate mixing of lipids and water due to
  ability to dissolve in both water and oil

27
Phospholipids in the Diet

• NOT essential nutrients!
• Examples phosphatidyl choline, lecithins
• common food sources
• eggs
• liver
• soybeans
• wheat germ
• peanuts

28
Classes of Lipids Sterols

• carbon atoms form RINGS
• do not contain fatty acids
• both lipophilic and hydrophobic
• not essential nutrients
• eg Cholesterol
• found only in animal foods
• eg Plant sterols

29
Functions of Sterols

• a) Component of cell membranes
• provide structure
• abundant in brain and nervous tissues
• b) Precursor to other substances
• steroid hormones (e.g. cortisol, testosterone,
  aldosterone, estrogen)
• Vitamin D
• bile acids

30
Lipid Digestion Absorption

• Mouth Stomach
• lingual lipase secreted in saliva, gastric lipase
  secreted by stomach- small contribution to
  digestion
• mechanical digestion of chewing and gastric
  mixing keep fat dispersed
• after 2 - 4 hours in the stomach, about 30 of
  lipids broken down to diglycerides and free fatty
  acids

31
Lipid Digestion Absorption

• Small intestine
• presence of fat in the small intestine stimulates
  secretion of
• - CCK
• - secretin
• - GIP
• bile contains bile salts phospholipids which
  emulsify fats

32
(No Transcript)
33
Lipid Digestion Absorption

• pancreatic lipase cleaves 1 fatty acid off
  triglycerides at a time, produces free fatty
  acids monoglycerides
• sterols remain unchanged by digestion or are
  esterified
• bile salts surround the products of lipid
  digestion forming micelles and transport digested
  lipid to intestinal cell surface
• bile salts are recycled
• monoglycerides fatty acids are absorbed by
  passive diffusion

34
Lipid Digestion Absorption

• monoglycerides long chain fatty acids reform
  triglycerides
• triglycerides, cholesterol, and phospholipids
  combine with proteins to form chylomicrons, a
  type of lipoprotein
• glycerol, short medium chain fatty acids are
  absorbed directly into the blood

35
Lipids in the Body Transport

• some short chain fatty acids ( glycerol) travel
  freely in blood
• most lipids require transporters called
  lipoproteins

36
Classes of Lipoproteins

• Chylomicrons
• transport diet derived lipids from small
  intestine to body tissues
• contain mostly triglyceride ( 90) and very
  little protein, lowest density
• the enzyme lipoprotein lipase splits off
  triglycerides from the chylomicron
• fatty acids may also be taken up by muscle cells

37
Classes of Lipoproteins

• Very Low Density Lipoproteins (VLDL)
• synthesized by liver intestines
• lipoprotein lipase splits off and hydrolyzes
  triglycerides from VLDL as it circulates
• as it loses triglycerides becomes an intermediate
  density lipoprotein (IDL)
• IDL are about 40 triglycerides
• pick up cholesterol from HDL
• return to the liver converted to LDL

38
Classes of Lipoproteins

• Low Density Lipoproteins (LDL)
• contain more than 50 cholesterol
• deliver cholesterol to the body cells
• LDL binds to a receptor on the surface of cell
  membranes, triggering the cell to engulf the LDL
  molecule
• contain a protein called Apo B
• facilitates cell uptake of cholesterol and
  triglycerides

39
Classes of Lipoproteins

• Low Density Lipoproteins (LDL) cont.
• other LDL receptors found on liver cells
• regulate blood levels of cholesterol
• receptors are blocked by saturated and trans
  fatty acids
• immune cells called macrophages also have
  scavenger receptors for LDL
• uptake of LDL by macrophages implicated in
  development of atherosclerosis

40
Classes of Lipoproteins

• High Density Lipoproteins (HDL)
• made in the liver intestines
• contains highest proportion of protein of all
  lipoproteins
• scavenges cholesterol and transfers the
  cholesterol to other lipoproteins (IDL) for
  return to the liver
• contains a protein called Apo E which activates
  receptors in the liver for uptake

41
(No Transcript)
42
Blood Lipids CVD

• elevated blood lipids are a risk factor for
  cardiovascular disease (CVD)
• assess risk by examining blood levels of
• triglycerides
• total cholesterol
• LDL
• HDL

43
Blood Lipids CVD

• Elevated Triglycerides
• linked to excess body fat, physical inactivity,
  cigarette smoking, Type II Diabetes, others
• most often seen in individuals with other lipid
  abnormalities
• optimal levels below 150 mg / dL blood

44
Blood Lipids CVD

• Elevated Total Cholesterol
• also linked to excess body fat, physical
  inactivity, cigarette smoking, Type II Diabetes,
  others
• optimal levels below 200 mg / dL blood

45
Blood Lipids CVD

• LDL BAD Cholesterol
• transport lipids from liver to the tissues
• elevated levels a risk factor for cardiovascular
  disease
• excess LDL in blood is susceptible to
  

46
Blood Lipids CVD

• LDL BAD Cholesterol cont.
• oxidized LDL (oxLDL) causes damage to blood
  vessel walls, initiating the development of
  atherosclerosis
• oxLDL taken up by macrophages through scavenger
  receptors
• macrophages become filled with lipids and are
  called foam cells
• results in build up of a fatty plaque on the
  blood vessel wall

47
(No Transcript)
48
Blood Lipids CVD

• LDL BAD Cholesterol cont.
• LDL particles may vary in size and density
• small dense LDL ? ? risk of CVD
• risk is also dependant on the specific proteins
  found within the LDL particle
• example ? risk for apo B and apo A-1
• optimal levels less than 100 mg / dL
• Think L less healthy or lethal

49
Blood Lipids CVD

• HDL GOOD Cholesterol
• transports lipids from tissues to the liver
• high levels ? risk of CVD
• low levels ? risk of CVD
• ratio of HDLLDL (or HDLtotal cholesterol) also
  important (? 12 low risk)
• regular physical activity helps ? HDL
• optimal levels greater than 60 mg / dl
• Think H healthy

50

• Note you cannot eat either LDL or HDL!

51
How does DIET influence blood lipids?

• Monounsaturated Fatty Acids
• associated with a ? risk of CVD
• may help lower triglycerides, total cholesterol
  LDL
• may make LDL particles less susceptible to
  oxidation
• may help increase HDL
• may also reduce other CVD risk factors
• know rich food sources of MUFA!

52
How does DIET influence blood lipids?

• Omega 3 Fatty Acids
• associated with a ? risk of CVD
• lower LDL triglycerides
• decrease blood pressure
• decrease blood clotting
• reduce inflammation
• know rich food sources of PUFA!

53
How does DIET influence blood lipids?

• Saturated Fatty Acids
• high dietary intake associated with ?d risk of
  CVD
• may increase CVD risk by ? HDL, ? LDL, ? total
  blood cholesterol
• know rich food sources!
• Dietary Cholesterol
• does not increase blood cholesterol as
  dramatically as saturated or trans fatty acids

54
How does DIET influence blood lipids?

• Trans Fatty Acids
• unsaturated fatty acids that have an abnormal
  arrangement of hydrogen atoms about a carbon
  double bond
• hydrogen atoms are opposite each other
• produced by the process of hydrogenation

trans
cis
55
How does DIET influence blood lipids?

• Hydrogenation
• addition of H to unsaturated fats
• Benefits
• less susceptible to spoilage
• changes texture
• Risks
• produces trans fatty acids

56
How does DIET influence blood lipids?

• Risks of Trans Fatty Acids
• ? LDL ? HDL
• Sources
• most margarines
• cakes, cookies, doughnuts, pastries, crackers
• meats dairy products
• chips other snack foods
• many brands of peanut butter
• deep-fried foods

57
ANY food that contains HYDROGENATED or PARTIALLY
HYDROGENATED VEGETABLE OIL or SHORTENING on its
ingredient list will likely contain trans fatty
acids.
58
Dietary Lipids Cancer

• link between dietary fat cancer is tenuous
• linked to excess consumption of saturated fat
• appear to act as a cancer promoter
• strong link between dietary fat intake prostate
  cancer
• studies linking dietary fat risk of breast
  cancer are inconclusive
• eating fish may protect against some cancers

59
Dietary Lipids Obesity

• fat contributes 9 kcal/g
• a high fat diet may be linked with excess energy
  consumption thus contributing to weight gain

Dietary Lipids Diabetes Mellitus

• a diet high in MUFA may be beneficial for
  managing blood glucose levels

60
Current Dietary Intakes

• gt ¼ of Canadians aged 31-50 obtain more than 35
  of their total calories from fat
• average fat intake of Canadians in 2002 was 34
  of total energy intake (dropped from 36 in 1992)
• BUT
• total food energy consumed by Canadians rose 18
  between 1992 2002
• this increase in average energy intake means
  Canadians are actually consuming more total grams
  of fat!

61
Recommended Intakes

• AMDR for Total Fat
• 20-35 of total energy intake
• Daily Values
• Total 65 g, Saturated 20 g
• Cholesterol 300 mg
• Linoleic Acid -?????
• AI 17 g/day (men), 12 g/day (women)
• AMDR 5-10 of total energy intake
• a-Linolenic Acid - ???
• AI 1.6 g/day (men), 1.1 g/day (women)
• AMDR 0.6-1.2 of total energy intake

62
Saturated fatty acids, trans fatty acids,
cholesterol have no known beneficial role in
preventing chronic disease and are not required
at any level in the diet
63
Dietary Tips

• Reducing Total Fat Intake
• remove fats from foods
• reduce use of fat in cooking
• use fat containing condiments in moderation
• replace high fat foods with low fat alternatives
• choose low fat milk and dairy products
• look for invisible fat

64
Dietary Tips

• Reduce Saturated Trans Fat Intake
• reduce intake of animal fats
• reduce intake of hydrogenated vegetable oil and
  products that contain it

65
65
66
Fat Replacements

• can be made from carbohydrate (including fiber),
  protein, or synthetic
• Olestra (Olean)
• derived from sucrose and fatty acids (called a
  sucrose polyester)
• too large to be digested by the enzymes of the
  human digestive tract ? therefore does not
  contribute any kilocalories
• Problems?

67
(No Transcript)