The Lipids: Triglycerides, Phospholipids, and Sterols

1
The Lipids Triglycerides, Phospholipids, and
Sterols

• Chapter 5

2
Fig. 5-CO, p. 132
3
Introduction

• Poor health
• Too much fat
• Too little fat (unlikely in U.S.)
• Too much of some kinds of fat
• Family of lipids
• Triglycerides- fats and oils
• Phospholipids
• Sterols

4
Overview of Fatty Acids and Triglycerides

• Energy provided per gram
• More carbons and hydrogens per oxygen
• Preview of lipids from diet
• Triglycerides 1 glycerol plus 3 fatty acids
• Fatty acids have even number of carbons
• Fatty acids are saturated or unsaturated
• Omega-3 and omega-6 fatty acids

5
Chemists View of Fatty Acids and Triglycerides

• Fatty acids
• Organic (carbon-based) acid
• Methyl group at one end acid group at other end
• Usually even number of carbons, 4-24
• 18-carbon fatty acids abundant in food
• Saturations
• Saturated full of hydrogens, no double bonds
• Unsaturated missing hydrogens

6
(No Transcript)
7
Acid end
Methyl end
Up to 22 more carbons
8
p. 138
9
Saturated Fatty Acids

• NO double bonds
• Solid at 77 F
• Found in meat, dairy, tropical fat
• Max. allowed is 1/3 total daily fat

10
Stearic Acid
Fully saturated, no double bonds
11
Stearic Acid
Zero double bonds
12
Polyunsaturated Fatty Acids (PUFAs)

• Omega-3 1st double bond is 3 carbons
• from methyl end ex linolenic acid
• fatty fishes
• Omega-6 1st double bond is 6 carbons
• from methyl end ex linoleic acid
• many vegetable oils
• Liquid at 77 F

13
PUFAs
Linolenic acid, an omega-3 fatty acid
Omega carbon at 3
Acid end
Methyl end
Linoleic acid, an omega-6 fatty acid
Omega carbon at 6
Acid end
Methyl end
14
Monounsaturated Fatty Acids (MUFAs)

• One double bond
• Most MUFA in diet are omega-9
• Oleic acid most common MUFA
• Olive, safflower, canola oils
• Liquid at 77 F

15
Impossible configuration
16
One Double Bond
Mono one point of unsaturation
17
Linoleic acid, an 18-carbon PUFA
2 double bonds
18
Linoleic acid
19
Double bond
Saturated fatty acids tend to stack together.
Consequently, saturated fats tend to be solid (or
more firm) at room temperature.
This mixture of saturated and unsaturated fatty
acids does not stack neatly because unsaturated
fatty acids bend at the double bond(s).
Consequently, unsaturated fats tend to be liquid
(or less firm) at room temperature.
20
(No Transcript)
21
Fatty Acids

• Distinction by location of double bonds
• Omega number is 1st double bond
• nearest the methyl end of the carbon chain
• Linolenic acid 3 dbl bonds, minus 6 H
• Linoleic acid 2 dbl bonds, minus 4 H
• Monounsaturated fatty acids
• Omega-9 groups

22
PUFAs in Food
Linolenic acid, an omega-3 fatty acid
Omega carbon at 3
Acid end
Methyl end
Linoleic acid, an omega-6 fatty acid
Omega carbon at 6
Acid end
Methyl end
23
Triglycerides (TG)

• Glycerol backbone
• Three fatty acids
• Formed via series of condensation reactions
• Usually contain mixture of fatty acids

24
Glycerol
25
How Triglycerides are Made
26
Glycerol three fatty acids
An H atom from glycerol and an OH group from a
fatty acid combine to create water, leaving the O
on the glycerol and the C at the acid end of each
fatty acid to form a bond.
27
Saturation vs Unsaturation

• Firmness
• Poly and Monounsaturated fats
• Saturated fats
• Length of carbon chain- shorter softer
• Stability
• Oxidation and spoilage of fats
• Saturated fats are more stable
• Antioxidants BHA, BHT, Vitamin E

28
Hydrogenation

• Adding H2 to PUFAs to reduce double bonds,
  making them more saturated / solid and more
  resistant to oxidation which leads to rancidity.
• Hydrogenation produces trans fatty acids

29
How to Make Trans from Poly with Hydrogen Gas
30
Hydrogenation

• Advantages
• Shelf life
• Texture improvement
• Disadvantages
• Acts like saturated fat in the blood,
• only worse

31
Cis- and Trans-
cis-fatty acid
trans-fatty acid
A cis-fatty acid has its hydrogens on the same
side of the double bond cis molecules fold back
into a U-like formation. Most naturally occuring
unsaturated fatty acids in foods are cis.
A trans-fatty acid has its hydrogens on the
opposite sides of the double bond trans
molecules are more linear. The trans form
typically occurs in partially hydrogenated foods
when hydrogen atoms shift around some double
bonds and change the configuration from cis to
trans.
32
Phospholipid (PL)

• Compound similar to a triglycerides but has a
  phosphate group and choline in place of one of
  the fatty acids
• Lecithin most common one

33
Phospholipid
From 2 fatty acids
The plus charge on the N is balanced by a
negative ion usually chloride.
From choline
From glycerol
From phosphate
34
Phospholipids

• Phospholipids
• Solubility in fat and water
• Emulsifiers in food industry (lecithin)
• Food sources- egg yolk, liver, soy, peanuts
• Roles in the Body
• Part of cell membranes
• Emulsifiers

35
Cell Membrane
Outside cell (ECF)
Glycerol heads
Fatty acid tails
Glycerol heads
Inside cell (ICF)
36
Sterols

• Cholesterol
• Food sources and production of 800-1500 mg/d by
  liver
• Plant sterols inhibit cholesterol absorption
• Body compounds made from cholesterol
• Bile acids
• Sex hormones
• Adrenal hormones
• Vitamin D

37
Cholesterol
Vitamin D3
38
Lipid Digestion

• Fats are hydrophobic
• Digestive enzymes are hydrophilic
• Goal of fat digestion
• Dismantle triglycerides into monoglycerides,
  fatty acids, and glycerol

39
Lipid Digestion
40
FAT
Mouth and salivary glands Some hard fats begin
to melt as they reach body temperature. The
sublingual salivary gland in the base of the
tongue secretes lingual lipase.
Salivary glands
Mouth
Stomach
Tongue
The acid-stable lingual lipase initiates lipid
digestion by hydrolyzing one bond of
triglycerides to produce diglycerides and fatty
acids. The degree of hydrolysis by lingual lipase
is slight for most fats but may be appreciable
for milk fats. The stomachs churning action
mixes fat with water and acid. A gastric lipase
accesses and hydrolyzes (only a very small amount
of) fat.
Sublingual salivary gland
Gallbladder
Stomach
Pancreatic duct
(Liver)
Pancreas
Common bile duct
Small intestine Bile flows in from the
gallbladder (via the common bile duct)
Bile
Fat
Emulsified fat
Pancreatic lipase flows in from the pancreas (via
the pancreatic duct)
Small intestine
Large intestine
Pancreatic (and intestinal) lipase
Emulsified fat (triglycerides)
Monoglycerides, glycerol, fatty acids (absorbed)
Large intestine Some fat and cholesterol,
trapped in fiber, exit in feces.
Fig. 5-12, p. 142
41
Lipid Digestion

• Mouth- minor
• Lingual lipase for dairy fat
• Stomach- minor
• Strong muscle contractions
• Gastric lipase hydrolyzes TG into diglycerides
  and fatty acids

42
Fat
Watery GI juices
Enzymes
In the stomach, the fat and watery GI juices tend
to separate. The enzymes in the GI juices cant
get at the fat.
43
Lipid Digestion Main Site

• Small intestine
• Cholecystokinin (CCK) signals
• gall bladder to release bile
• Bile acts as emulsifier
• Pancreatic lipases
• Hydrolysis
• Triglycerides and phospholipids
• Bile routes
• Blood cholesterol levels

44
Bile as an Emulsifier
Bile acid made from cholesterol (hydrophobic)
Bound to an amino acid from protein (hydrophilic)
45
Emulsification of Fat by Bile
Enzyme
Fat
Fat
Watery GI juices
Bile
Emulsified fat
Emulsified fat
Emulsified fat
Enzymes
In the stomach, the fat and watery GI juices tend
to separate. The enzymes in the GI juices cant
get at the fat.
When fat enters the small intestine, the
gallbladder secretes bile. Bile has an affinity
for both fat and water, so it can bring the fat
into the water.
Biles emulsifying action converts large fat
globules into small droplets that repel each
other.
After emulsification, more fat is exposed to the
enzymes, making fat digestion more efficient.
46
Bile acting like Soap
Fat
Bile
Emulsified fat
47
Enterohepatic Circulation of Bile
48

49
Enzyme
Emulsified fat
After emulsification, more fat is exposed to the
pancreatic lipases, making fat digestion
(hydrolysis) more efficient.
50
Hydrolysis of a Triglyceride
Bonds break
Bonds break
Triglyceride
Monoglyceride 2 fatty acids
The triglyceride and two molecules of water are
split. The H and OH from water complete the
structures of two fatty acids and leave a
monoglyceride.
These products may pass into the intestinal
cells, but sometimes the monoglyceride is split
with another molecule of water to give a third
fatty acid and glycerol. Fatty acids,
monoglycerides, and glycerol are absorbed into
intestinal cells.
51
Lipid Absorption

• Directly into bloodstream
• Glycerol and short- medium-chain fatty acids
• Micelles- fatty acids, monodiglycerides, bile,
  cholesterol diffuse into intestinal cells
• Reassembly of triglycerides from micelles
• Chylomicrons- protein vehicle picking up TGs,
  cholesterol, phospholipids in S.I.
• Intestinal cells release chylomicrons into
  lymphatic system

52
Absorption of Fat
53
Small intestine
Monoglyceride

Stomach
Short-chain fatty acids
Micelle
Medium-chain fatty acids
2
Protein
1
Glycerol
Triglyceride
Chylomicrons
Long-chain fatty acids
Chylomicron
Capillary network
Lacteal (lymph)
2
Large lipids such as monoglycerides and
long-chain fatty acids combine with bile, forming
micelles that are sufficiently water soluble to
penetrate the watery solution that bathes the
absorptive cells. There the lipid contents of the
micelles diffuse into the cells.
Blood vessels
Via lymph to blood
Via blood to liver
Glycerol and small lipids such as short- and
medium-chain fatty acids can move directly into
the bloodstream.
1
54
Lipid Transport

• Four main types of lipoproteins
• Chylomicrons
• Largest and least dense (more fat, less prot.)
• Shrink as they transport diet-derived lipids
• Liver removes remnants from blood
• Very-low-density lipoproteins (VLDL)
• Made in the liver, 50 TG
• Cells take TG until VLDL becomes LDL

55
Lipid Transport

• Four main types of lipoproteins
• Low-density lipoproteins (LDL)
• More cholesterol than TG
• Distribute Chol, TG and PL for cell needs
• Liver regulation
• High-density lipoproteins (HDL)
• Made by liver
• Removes cholesterol from cells
• Carry cholesterol to liver for recycling
• Anti-inflammatory properties

56

Protein
Phospholipid

A typical lipoprotein contains an interior of
triglycerides and cholesterol surrounded by
phospholipids. The phospholipids fatty acid
tails point towards the interior, where the
lipids are. Proteins near the outer ends of the
phospholipids cover the structure. This
arrangement of hydrophobic molecules on the
inside and hydrophilic molecules on the outside
allows lipids to travel through the watery fluids
of the blood.
Cholesterol
Triglyceride
100 80 60 40 20 0
Protein
Chylomicron
LDL
Percent
Cholesterol
Phospholipid
VLDL
Triglyceride
Chylomicron
VLDL
LDL
HDL
Chylomicrons contain so little protein and so
much triglyceride that they are the lowest in
density.
HDL
Very-low-density lipoproteins (VLDL) are half
triglycerides, accounting for their very low
density.
This solar system of lipoproteins shows their
relative sizes. Notice how large the fat-filled
chylomicron is compared with the others and how
the others get progressively smaller as their
proportion of fat declines and protein increases.
Low-density lipoproteins (LDL) are half
cholesterol, accounting for their implication in
heart disease.
High-density lipoproteins (HDL) are half protein,
accounting for their high density.
57
Lipid Transport
58
Role of Triglycerides

• Provide the cells with energy
• 9 kcalories per gram
• Virtually unlimited ability to store fat energy
  in body
• Adipose tissue secrete adipokines
• regulate energy balance (leptin)
• Insulin resistance and inflammation (resistan)
• Skin insulation, shock absorption, cell
  membranes, and cell signaling pathways

59
Essential Fatty Acids

• Linoleic acid Omega-6 fatty acid
• Starter for arachidinic acid
• Sources- vegetable oils and meat
• Linolenic acid Omega-3 fatty acid
• Sources- fish, flaxseed
• Starter for DHA , EPA
• Eicosanoids made from arachidinic and EPA,
  regulate blood pressure, clotting
• Fatty acid deficiencies

60
Lipid Metabolism (Burning Fat)

• Adipose cells store fat after meals
• Lipoprotein lipase in adipose hydrolyzes
  triglycerides from lipoproteins passing by and
  releases them into adipose cells
• Triglycerides reassembled inside adipose cells
  for storage
• Fat supplies 60 of energy during rest
• 1 lb body fat 3500 kcal
• Requires CHO to break down fat

61
Health Effects of Lipids

• Heart disease
• Elevated blood cholesterol
• Saturated fat increase LDL cholesterol, promote
  blood clotting
• Dietary choices
• Trans-fats increase LDL cholesterol
• Dietary cholesterol

62
Health Effects of Lipids

• Heart disease
• Monounsaturated fats
• Replace saturated and trans fats
• Reduces blood cholesterol
• Dietary sources
• Omega-3 fats
• Benefits
• Dietary sources
• Omega-6 to omega-3 ratio

63
Health Effects of Lipids

• Cancer
• Promotion rather than initiation of cancer
• Dietary fat and cancer risk
• Differs for various types of cancer
• Obesity
• Cutting fat from diet reduces kcalories
• Dietary recommendations

64
Recommended Intakes of Fat

• DRI and Dietary Guidelines
• Diet low in saturated and trans fat
• Diet low in cholesterol
• 20 to 35 percent of daily energy from fat
• AI set for linoleic and linolenic acids
• Daily Values (DV) on food labels
• Saturated fat and cholesterol
• Risk of insufficient fat intake

65
From Guidelines to Groceries

• Fat-soluble vitamins
• A, D, E, and K
• Flavor, texture, and palatability
• Meats and meat alternatives
• Selections
• Milk and milk products
• Selections

66
From Guidelines to Groceries

• Vegetables, fruits, and grains
• Lowers consumption of various fats in the diet
• Invisible fat
• Fried and baked goods
• Choose wisely
• Unprocessed foods

67
From Guidelines to Groceries

• Fat replacers
• Types
• Risks
• Read food labels
• Total fat, saturated fat, trans fat, and
  cholesterol
• Compare products
• Daily Value vs. kcalories from fat

68
Butter and Margarine Labels Compared
69
Highlight 5

• High-Fat Foods Friend or Foe?

70
Guidelines for Fat Intake

• Limit saturated fat and trans fat intake
• Moderate kcalories
• Enough fat for good health
• Not too much of the harmful fats
• DRI recommendations
• Compatible with low rates of disease

71
High-Fat Foods and Heart Health

• Olive oil
• Benefits for heart health
• Replace saturated fats
• Nuts
• LDL cholesterol
• Fat composition
• Benefits for heart health
• Cautious advice for dietary inclusion

72
High-Fat Foods and Heart Health

• Fish
• Omega-3 fatty acids
• Benefits for heart health
• Environmental contaminants
• Dietary recommendations

73
High-Fat Foods and Heart Health
74
High-Fat Foods and Heart Disease

• Saturated fat and LDL cholesterol
• Sources of saturated fat in the U.S.
• Meats
• Whole milk products
• Tropical oils
• Zero saturated fat is not possible
• Trans fat
• Limit hydrogenated foods

75
High-Fat Foods and Heart Disease
76
High-Fat Foods and Heart Disease
77
High-Fat Foods and Heart Disease
78
The Mediterranean Diet

• Traditionally
• Low in saturated fat
• Very low in trans fat
• Rich in unsaturated fat
• Rich in complex carbohydrate and fiber
• Rich in nutrients and phytochemicals
• Benefits for heart disease risk