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

2. Objectives for Chapter 5
Recognize the chemistry of fatty acids and triglycerides and differences between saturated and unsaturated fats.
Describe the structure of a fatty acid and the effects of chain length and saturation on the properties of the fat.
Describe the triglyceride.
List and describe the three types of fatty acids found in foods.
Explain the structure of the omega-3 and -6 fatty acids.
Describe the chemistry, food sources, and roles of phospholipids and sterols.
Summarize fat digestion, absorption, and transport.
Trace the digestion of lipids including identification of enzymes needed and the role of bile.
Describe the absorption of lipids into the intestine and the formation of the chylomicron.
Describe the role of the liver in the production of lipoproteins.
Explain the health implications of LDL and HDL and the factors that raise or lower levels of these lipoproteins.
Outline the major roles of fats in the body, including a discussion of essential fatty acids and the omega fatty acids.
Identify the uses of triglyceride in the body.
Identify the essential fatty acids and their role in the formation of eicosanoids.
Explain the relationships among saturated fat, trans fat, and cholesterol and chronic diseases, noting recommendations.
Explain the relationships between monounsaturated and polyunsaturated fats and health, noting recommendations.
Identify which fats support health and which impair it.
Name practical suggestions for food selections to replace saturated and trans fats with monounsaturated and polyunsaturated fats.

3. Introduction Poor health Family of lipids Too much fat Too little fat
Too much of some kinds of fat
Family of lipids
Triglycerides
Phospholipids
Sterols

4. Chemist’s View of Fatty Acids and Triglycerides
Energy provided per gram
More carbons and hydrogens
Preview of lipids
Triglycerides: glycerol and 3 fatty acids
Fatty acids: even number of carbons
Fatty acids: saturated or unsaturated
Omega-3 and omega-6 fatty acids
18-carbon polyunsaturated fatty acids

5. Chemist’s View of Fatty Acids and Triglycerides
Methyl group at one end; acid group at other end
Usually even number of carbons
18-carbon fatty acids abundant in food
Saturations
Saturated – full of hydrogens
Unsaturated – missing hydrogens
COOH
H3C

6. 18-Carbon Fatty Acids
Yes, I will expect you to know this chart!

7. Chemist’s View of Fatty Acids and Triglycerides
Naming fatty acids
Location of double bonds
Nearest the methyl end of the carbon chain
Omega number
Monounsaturated fatty acids
Omega-9 groups (i.e. oleic)
Polyunsaturated fatty acids
Linolenic acid = Ω3
Linoleic acid = Ω6

8. Omega-3 and Omega-6 Fatty Acids Compared

9. Chemist’s View of Fatty Acids and Triglycerides
Glycerol backbone
Three fatty acids
Formed via series of condensation reactions
Usually contain mixture of fatty acids

10. Condensation of Glycerol and Fatty Acids to Form a Triglyceride

11. Chemist’s View of Fatty Acids and Triglycerides
Chemistry  Characteristics
Firmness
More saturated = more firm
Longer chain = more firm
Examples
Stability
Oxidation causes spoilage of fats
More saturated = more stable
Air-tight, non-metallic, refrigerated, antioxidants, hydrogenation

12. Diagram of Saturated & Unsaturated Fatty Acids Compared

13. Fatty Acid Composition of Common Food Fats

14. Chemist’s View of Fatty Acids and Triglycerides
Chemistry  Characteristics
Hydrogenation
Advantages: prolongs shelf life, improves texture (thicker, spreadable, flakey, etc)
Trans-fatty acids
Configurations – cis and trans
Similarity to other types of fat
Naturally occurring
Conjugated linoleic acid (CLA)

15. Hydrogenation

16. Cis- and Trans-Fatty Acids Compared

18. Chemist’s View of Phospholipids and Sterols
Solubility in fat and water
Emulsifiers in food industry
Lecithin (most common)
Food sources
Eggs, soybeans, peanuts
Roles
Part of cell membranes
Emulsifiers
Cell membranes – help fat-soluble substances (vitamins and hormones) to pass easily in and out of cells)
Emulsifiers in the body – keep fats suspended in the blood and body fluids

19. Lecithin

20. Chemist’s View of Phospholipids and Sterols
Food sources
Cholesterol
Plant sterols
Roles of sterols
Body compounds made from cholesterol
Bile acids, hormones, vitamin D, cholesterol
Plant sterols are structurally similar to cholesterol, interfere with its absorption

22. Lipid Digestion Fats are hydrophobic Goal of fat digestion
Digestive enzymes are hydrophilic
Goal of fat digestion
Dismantle triglycerides
Monoglycerides, fatty acids, and glycerol

24. Lipid Digestion Mouth Stomach Lingual lipase
Strong muscle contractions
Gastric lipase

25. Lipid Digestion Small intestine Bile routes Cholecystokinin (CCK)
Gall bladder releases bile
Bile acts as emulsifier
Pancreatic lipase
Hydrolysis
Triglycerides and phospholipids
Bile routes
Blood cholesterol levels

26. Fat Watery GI juices Fat Enzyme Bile Emulsified fat Emulsified fat
Enzymes
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 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.
Stepped Art
Figure 5-12 p140

27. Hydrolysis of a Triglyceride

28. 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 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.
In the colon, bile that has been trapped by soluble fibers is lost in feces.
Stepped Art
Figure 5-14 p141

29. Lipid Absorption Glycerol, short- & medium-chain fatty acids
Directly into bloodstream
Monoglycerides, long-chain fatty acids
Lymphatic system

30. Lipid Absorption Monoglycerides, long-chain fatty acids
Emulsified = micelle (spherical complex)
Micelles diffuse into intestinal cells
Reassembly of triglycerides
Packed with proteins into chylomicrons (transport vehicles)  lymphatic system
Chylomicrons enter bloodstream at thoracic duct

31. Absorption of Fat

32. Lipid Transport
Transport of lipids through water-based blood requires transport vehicles
Four main types of lipoproteins
Chylomicrons
Largest and least dense
Transport diet-derived lipids
Liver removes remnants from blood

33. Lipid Transport Four main types of lipoproteins
Very-low-density lipoproteins (VLDL)
Made in the liver
Proportion of lipid shift as cells remove triglycerides
Low-density lipoproteins (LDL)
Cells use for energy, make hormones, new membranes
Liver regulation – special receptors to get LDL out of circulation

34. Lipid Transport Four main types of lipoproteins Health implications
High-density lipoproteins (HDL)
Remove cholesterol from cells
Carry cholesterol to liver for recycling
Anti-inflammatory properties
Health implications
LDL linked to heart disease and heart attacks
HDL has protective effect

35. Sizes and Compositions of the Lipoproteins

36. Lipid Transport via Lipoproteins

38. Role of Triglycerides Provide the cells with energy Adipose tissue
Virtually unlimited ability to store fat energy in body (adipose cells)
Adipose tissue
Secretes adipokines (hormones)
Regulate energy balance
Type and quantity of secretions change when body fat is extreme (high or low)
Skin insulation, shock absorption, cell membranes, and cell signaling pathways

39. An Adipose Cell

40. Essential Fatty Acids Must be supplied by the diet
Linoleic acid (Ω6)
Linolenic acid (Ω3)
Can be used to make other fatty acids

41. Essential Fatty Acids Linoleic acid – Ω6 fatty acid
Sources: corn, safflower, soybean oils; walnuts; mayonnaise; pumpkin seeds
Linolenic acid – Ω3 fatty acid
Sources: fatty fish; flaxseed; walnuts
DHA & EPA (linolenic derivatives)
Essential for normal growth, visual acuity, cognitive development
Might: prevention/treatment of heart disease

42. Essential Fatty Acids Eicosanoids (Ω3, Ω6 derivatives) “Hormonelike”
Affect only locally
Different effects on different cells
Health benefits
Ω3: ↓blood pressure, prevent blood clots and irregular heartbeats, ↓inflammation
Ω6: promote clot formation, inflammation, blood vessel constriction (good during injury!); ↓LDL, improve insulin resistance

43. Essential Fatty Acids Ω 6: Ω3 ratio Fatty acid deficiencies
Compete, opposite action
4:1 to 10:1
Fatty acid deficiencies
Infants/children, anorexia nervosa
Symptoms: growth retardation, reproductive failure, skin lesions, neurological and visual problems, kidney/liver disorders

44. A Preview of Lipid Metabolism
Adipose cells store fat after meals
Lipoprotein lipase (LPL)
Hydrolyzes triglycerides
Triglycerides reassembled inside adipose cells
Using fat for energy
Protein sparing
Energy deprivation (fasting)
Endurance exercise

46. Health Effects of Saturated Fats, Trans Fats, and Cholesterol
Current American diet
20% of kcal = solid fats
Blood lipid profile
TG, cholesterol, VLDL, LDL, HDL

47. Health Effects of Saturated Fats, Trans Fats, and Cholesterol
Heart disease
Elevated blood cholesterol
Saturated fat – ↑LDL cholesterol, promote blood clotting
Dietary choices
12, 14, 16 carbons vs. 18 carbons
Meat, milk, milk products
Trans fats – ↑LDL cholesterol
Dietary cholesterol

48. Health Effects of Saturated Fats, Trans Fats, and Cholesterol
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

49. Recommended Intakes of Saturated Fat, Trans Fat, & Cholesterol
DRI and Dietary Guidelines
20-35% kcal from fat
<10% from sat fat
<1% from trans fat
<300mg cholesterol
Recommended to consume at least 1 tsp of fat per meal

51. Health Effects of Monounsaturated & Polyunsaturated Fats
Heart disease
Replace saturated fats with unsaturated fats
Regular consumption of omega-3 fatty acids
Suppress inflammation
Cancer
Omega-3 fatty acids from food
Supplements
1g EPA, 1g DHA
Can cause excessive bleeding

52. Replacing Saturated with Unsaturated Fat

53. Recommended Intakes of Mono- & Polyunsaturated Fats
20 to 35 percent of kcalories from fat
Includes essential fatty acids
AI have been established
DRI
Linoleic acid – 5-10% of daily energy
Linolenic acid – % of daily energy

54. From Guidelines to Groceries
Fat-soluble vitamins
A, D, E, and K
Flavor, texture, and palatability
Protein foods
Choose lean cuts, fatty fish, grill/bake/broil
Milk and milk products
Choose low-fat/fat-free, fermented

55. Cutting Fat Cuts kCalories and Saturated Fat

56. From Guidelines to Groceries
Vegetables, fruits, and grains
Lowers consumption of various fats
Beware of fried, added fats
Solid fats and oils
Fried and baked goods
Choose wisely
Unprocessed foods

57. From Guidelines to Groceries
Read food labels
Total fat, saturated fat, trans fat, and cholesterol
Compare products
Fat replacers
Artificial fats (Olestra)
Risks: vitamin loss, cramping, loose stool

58. From Guidelines to Groceries
Make Heart-Healthy Choices (pg 152)
Calculating personal Daily Value for Fat
% DV for fat on food labels = 2000 kcal diet
Need to translate to YOUR kcal level
Ex: 1800 kcal, 30% kcal from fat
1800 total kcal X 0.30 from fat = 540 fat kcal
540 fat kcal / 9 kcal/g = 60g fat

60. High-Fat Foods – Friend or Foe?
Highlight 5:
Bonus Learning!

61. 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

62. 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

63. High-Fat Foods and Heart Health
Fish
Omega-3 fatty acids
Benefits for heart health
Environmental contaminants
Dietary recommendations

64. 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

65. High-Fat Foods and Heart Disease

66. High-Fat Foods and Heart Disease

67. 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

68. Mediterranean Diet Plan