1. The Lipids: Triglycerides, Phospholipids, and Sterols
Chapter 5

2. Fig. 5-CO, p. 132

3. Introduction Poor health Family of lipids 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. Chemist’s View of Fatty Acids and Triglycerides
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

7. Acid end Methyl end Up to 22 more carbons Figure 5.1: Acetic Acid.
Acetic acid is a two-carbon organic acid.
Up to 22 more carbons

8. At room temperature, saturated fats (such as those commonly found in butter and other animal fats) are solid, whereas unsaturated fats (such as those found in vegetable oils) are usually liquid.
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 (PUFA’s)
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. PUFA’s Linolenic acid, an omega-3 fatty acid
Omega carbon at #3
Acid end
Methyl end
Linoleic acid, an omega-6 fatty acid
Figure 5.2: Omega-3 and Omega-6 Fatty Acids Compared.
The omega number indicates the position of the first double bond in a fatty acid, counting from the methyl (CH3) end. Thus an omega-3 fatty acid’s first double bond occurs three carbons from the methyl end, and an omega-6 fatty acid’s first double bond occurs six carbons from the methyl end. The members of an omega family may have different lengths and different numbers of double bonds, but the first double bond occurs at the same point in all of them. These structures are drawn linearly here to ease counting carbons and locating double bonds, but their shapes actually bend at the double bonds, as shown in Figure 5-8 (p. 139).
Omega carbon at #6
Acid end
Methyl end

14. Monounsaturated Fatty Acids (MUFA’s)
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. This mixture of saturated and unsaturated fatty acids does not
Double bond
Figure 5.5: Diagram of Saturated and Unsaturated Fatty Acids Compared.
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. Figure 5.6: Comparison of Dietary Fats.
Most fats are a mixture of saturated, monounsaturated, and polyunsaturated fatty acids.

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. PUFA’s in Food Linolenic acid, an omega-3 fatty acid
Omega carbon at #3
Acid end
Methyl end
Linoleic acid, an omega-6 fatty acid
Figure 5.2: Omega-3 and Omega-6 Fatty Acids Compared.
The omega number indicates the position of the first double bond in a fatty acid, counting from the methyl (CH3) end. Thus an omega-3 fatty acid’s first double bond occurs three carbons from the methyl end, and an omega-6 fatty acid’s first double bond occurs six carbons from the methyl end. The members of an omega family may have different lengths and different numbers of double bonds, but the first double bond occurs at the same point in all of them. These structures are drawn linearly here to ease counting carbons and locating double bonds, but their shapes actually bend at the double bonds, as shown in Figure 5-8 (p. 139).
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. Figure 5.4: Condensation of Glycerol and Fatty Acids to Form a Triglyceride.
To make a triglyceride, three fatty acids attach to glycerol in condensation reactions.
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 PUFA’s 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 Disadvantages Shelf life Texture improvement
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.
Figure 5.8: Cis- and Trans-Fatty Acids Compared.
This example shows the cis configuration for an 18-carbon monounsaturated fatty acid (oleic acid) and its corresponding trans configuration (elaidic acid).

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.
Figure 5.9: Lecithin.
Lecithin is one of the phospholipids. Notice that a molecule of lecithin is similar to a triglyceride but contains only two fatty acids. The third position is occupied by a phosphate group and a molecule of choline. Other phospholipids have different fatty acids at the upper two positions and different groups attached to phosphate.
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
Figure 5.10: Phospholipids of a Cell Membrane.
A cell membrane is made of phospholipids assembled into an orderly formation called a bilayer. The fatty acid “tails” orient themselves away from the watery fluid inside and outside of the cell. The glycerol and phosphate “heads” are attracted to the watery fluid.
Glycerol heads
Inside cell (ICF)

36. Sterols Cholesterol Body compounds made from cholesterol
Food sources and production of 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 Figure 5.11: Cholesterol.
The fat-soluble vitamin D is synthesized from cholesterol; notice the many structural similarities. The only difference is that cholesterol has a closed ring (highlighted in red), whereas vitamin D’s is open, accounting for its vitamin activity. Notice, too, how different cholesterol is from the triglycerides and phospholipids.
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. Sublingual salivary gland Gallbladder
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 stomach’s 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)
Common bile
duct
Pancreas
Small intestine
Bile flows in from the gallbladder (via the common bile duct):
Bile
Fat
Figure 5.12: Fat Digestion in the GI Tract.
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
Figure 5.14: Emulsification of Fat by Bile.
Like bile, detergents are emulsifiers and work the same way, which is why they are effective in removing grease spots from clothes. Molecule by molecule, the grease is dissolved out of the spot and suspended in the water, where it can be rinsed away.
In the stomach, the fat and watery GI juices tend to separate. The enzymes in the GI juices can’t 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)
Figure 5.13: A Bile Acid.
This is one of several bile acids the liver makes from cholesterol. It is then bound to an amino acid to improve its ability to form spherical complexes of emulsified fat (micelles). Most bile acids occur as bile salts, usually in association with sodium, but sometimes with potassium or calcium.

45. Emulsification of Fat by Bile
Enzyme
Watery GI juices
Bile
Emulsified fat
Emulsified fat
Enzymes
Emulsified fat
In the stomach, the fat and watery GI juices tend to separate. The enzymes in the GI juices can’t 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.
Bile’s 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.
Figure 5.14: Emulsification of Fat by Bile.
Like bile, detergents are emulsifiers and work the same way, which is why they are effective in removing grease spots from clothes. Molecule by molecule, the grease is dissolved out of the spot and suspended in the water, where it can be rinsed away.

46. Bile acting like Soap Fat Bile Emulsified fat
Figure 5.14: Emulsification of Fat by Bile.
Like bile, detergents are emulsifiers and work the same way, which is why they are effective in removing grease spots from clothes. Molecule by molecule, the grease is dissolved out of the spot and suspended in the water, where it can be rinsed away.

47. Enterohepatic Circulation of Bile

48. In the gallbladder, bile is stored.
In the liver, bile is
made from cholesterol.
In the small intestine, bile emulsifies fats.
Bile reabsorbed
into the blood
Figure 5.16: Enterohepatic Circulation.
Most of the bile released into the small intestine is reabsorbed and sent back to the liver to be reused. This cycle is called the enterohepatic circulation of bile. Some bile is excreted.
• enteron = intestine
• hepat = liver
In the colon, bile that has been trapped by soluble fibers is lost in feces.

49. After emulsification, more fat is exposed
Enzyme
Emulsified fat
Figure 5.14: Emulsification of Fat by Bile.
Like bile, detergents are emulsifiers and work the same way, which is why they are effective in removing grease spots from clothes. Molecule by molecule, the grease is dissolved out of the spot and suspended in the water, where it can be rinsed away.
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
Figure 5.15: Digestion (Hydrolysis) of a Triglyceride.
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 TG’s, cholesterol, phospholipids in S.I.
Intestinal cells release chylomicrons into lymphatic system

52. Absorption of Fat

53. Short-chain fatty acids Micelle Medium-chain fatty acids 2 Protein 1
Small intestine
Monoglyceride
Stomach
Short-chain fatty acids
Micelle
Medium-chain fatty acids 2
Protein 1
Glycerol
Triglyceride
Chylomicrons
Chylomicron
Long-chain fatty acids
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
Figure 5.17: Absorption of Fat.
The end products of fat digestion are mostly monoglycerides, some fatty acids, and very little glycerol. Their absorption differs depending on their size. (In reality, molecules of fatty acid are too small to see without a powerful microscope, whereas villi are visible to the naked eye.)
Via lymph to blood
Via blood to liver 1
Glycerol and small lipids such as short- and medium-chain fatty acids can move directly into the bloodstream.

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
Protein
Chylomicron
LDL
Percent
Cholesterol
Figure 5.18: Sizes and Compositions of the Lipoproteins.
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
Figure 5.19: Lipid Transport via Lipoproteins.

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
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

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. High-Fat Foods – Friend or Foe?
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
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