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

2. Introduction
Poor health from fat consumption is seen when a person consumes either
Too much fat
Too little fat
Too much of some kinds of fat
Lipids = Fat
Family of lipids
Triglycerides (TG) (fats & oils)*
Phospholipids
Sterols
Moderation and balance is key* however we are a society of abundance, people are likely to consume too much fat
TG most abundant in foods and in body

3. Chemist’s View of Fatty Acids and Triglycerides
Lipids =
TG, Phosolipids, and sterols
Composed of C, H, and O
Have more C & H = supply more E per gram
Most are TG w/ glycerol backbones and three fatty acids (f.a.)

4. Chemist’s View of Fatty Acids and Triglycerides
F.A. vary in C chain lengths, degree of unsaturation, and # of double bonds (d.b.)
Trans-fatty acids

5. Chemist’s View of Fatty Acids and Triglycerides
Preview of lipids
Triglycerides: glycerol and 3 fatty acids
Fatty acids: even number of carbons
4-24Cs; 18C most common in foods
Saturated or unsaturated
Mono or polyunsaturated

6. Chemist’s View of Fatty Acids and Triglycerides
Organic acid
Methyl group (CH3) at one end; acid group (COOH) at other
Usually even number of Cs
Saturation

7. Chemist’s View of Fatty Acids and Triglycerides
Unsaturated
Monounsaturated f.a. :
Lack 2H atoms & have 1 d.b.
When most of the f.a.s are monounsat its called a monounsaturated fat
Polyunsaturated f.a.s (PUFA)
Lack 4 or more Hs & have at least 2 or more d.b.
When most of the f.a.s are polyunsaturated its called a polyunsaturated fat

8. Chemist’s View of Fatty Acids
Location of d.b.
Nearest the methyl end of the carbon chain
Assigned an Omega number
Omega- 3-polyunsat f.a.
Linolenic acid are essential f.a.
Soybean and canola oils, flaxseed, walnuts
Omega- 6-polyunsat f.a.
Linoleic acids are essential f.a.
Vegetable, i.e. sunflower, safflower, corn, and soy bean oils
Monounsaturated fatty acids
Omega-9 groups
Oleic acid most predominate in diet
Olive, canola oils
Essential = must obtain from diet/outside source; body can not make

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

10. Chemist’s View of Fatty Acids and Triglycerides pg 137

11. Chemist’s View of Fatty Acids and Triglycerides
Degree of unsaturation
Firmness
Polyunsaturated fats
Saturated fats
Length of carbon chain
Stability
Sat fat is more resistant to oxidation
monounsat fat is slightly less susceptible to spoilage
Polyunsat fat spoils most readily
Protection from rancidity:
Polyunsat-liquid at room
Sat-solid at room temp
Shorter f.a.s are softer at room temp than longer chains
Oxidation: process of a substance combining with O; loss of e-

12. Chemist’s View of Fatty Acids and Triglycerides
Degree of unsaturation
Hydrogenation
Trans-fatty acids
Hydrogenation- addition of H molecules; increases shelf life…yields trans-fatty acids
Cis-H next to the db are on same side of C chain
Trans-H next to db are on opposite sides of the C chain
CLA-naturally occurring trans fat may have health benefits; not included under trans fat on label

13. Chemist’s View of Fatty Acids and Triglycerides

14. Chemist’s View of Fatty Acids and Triglycerides

15. Chemist’s View of Phospholipids and Sterols
Contain glycerol, 2 f.a. and a phosphate group with a molecule of choline
Solubility in fat and water
Emulsifiers in food industry
Roles
Emulsifier-substance with both water-soluble and fat-soluble portions that promote the mixing of oils and fats in watery soln

16. Chemist’s View of Phospholipids and Sterols
Food sources
Cholesterol
Plant sterols
Roles of sterols
Starting material for bile acids, sex hormones, adrenal hormones, and vit. D
Structural component of cell membranes
Liver produces mg cholesterol per day
Atherosclerosis
Atherosclerosis- disease that causes heart attacks. Occurs when cholesterol forms plaque deposits in the artery wall. Leads to heart attacks and stroke

17. Lipid Digestion Fats are hydrophobic Goal of fat digestion
Tend to separate from watery fluids in GI tract
Digestive enzymes are hydrophilic
Goal of fat digestion
Dismantle triglycerides for body to absorb and use
Hydro=water
Phobia= fear
Lipo= lipid
Philie= love

19. Lipid Digestion Mouth Stomach
Lingual lipase released by salivary glands
Stomach
Strong muscle contractions disperse fat into smaller droplets
Fat then exposed to Gastric lipase
-ase: enzyme

20. Lipid Digestion Small intestine Cholecystokinin (CCK)
Pancreatic and intestinal enzymes
Phospholipids are hydrolyzed
Sterols are absorbed
Bile routes
Enterohepatic circulation
Soluble fibers are effective
in trapping some bile and
excreting it from the body thru the large intestine
Pancreatic lipase is major-fat digesting enzyme
Enteron= intestine
Hepat= liver

21. Emulsification of Fat by Bile

22. Hydrolysis of a Triglyceride

23. Enterohepatic Circulation of Bile

24. Lipid Absorption Directly into bloodstream Lymphatic system
Glycerol and short- & medium-chain fatty acids diffuse and are re-absorbed directly into the bloodstream
Lymphatic system
Larger molecules, Monoglycerides and long-chain f.a.s, form micelles that get reabsorbed, and are reformed into new triglycerides. With protein they are transported by chylomicrons
When packaged with protein it’s then transported so that cells all over body may select needed lipids
Micelles-emulsified fat droplets formed by molecules of bile surrounding monoglycerides and fa

25. Lipid Transport
Lipid transport is made possible by a group of vehicles known as lipoproteins
Four main types of lipoproteins
Chylomicrons
Very-low-density lipoproteins (VLDL)
Low-density lipoproteins (LDL)
High-density lipoproteins (HDL)

27. Health implications
High LDL is associated with higher risk of heart attack and is known as a “bad” cholesterol
High HDL seems to have a protective effect and is known as “good” cholesterol
Factors that lower LDL and raise HDL
Genes influence lipopro activity

28. Role of Triglycerides Provide the cells with energy Adipose tissue
9 kcalories per gram
Adipose tissue
Virtually unlimited ability to store fat energy in body
Secretes hormones
Skin insulation, shock absorption, cell membranes, and cell signaling pathways

29. Essential Fatty Acids Linoleic acid – Omega-6 fatty acid
Linolenic acid – Omega-3 fatty acid
EPA & DHA-important for eyes, brain, and heart
Fatty acid deficiencies
Rare in US and Canada
Occur in infants and children with fat-free or low-fat diets

30. A Preview of Lipid Metabolism
Adipose cells store fat after meals
Lipoprotein lipase
Triglycerides reassembled inside adipose cells
Using fat for energy
Hormone-sensitive lipase inside the adipose cells hydrolyzes TG when needed for E
During fasting the body metabolizes fat, but requires CHO and pro for complete fat breakdown
Ketone bodies can be made from fat fragments

31. Health Effects of Lipids
Heart disease
Elevated blood cholesterol
Saturated fat
Dietary choices
Trans-fats
Dietary cholesterol

32. 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
Benefits-reduce risk of heart disease and stroke, support immune funx, defend against inflammation

33. Health Effects of Lipids
Cancer
Promotion rather than initiation of cancer
Dietary fat and cancer risk
Obesity
Cutting fat from diet reduces kcalories

34. 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

35. From Guidelines to Groceries
Very lean and lean options of meat and meat alternative products
Fat-free and low-fat milk products
Wide variety of vegetables, fruits, and whole grains
Avoid invisible fat from high-fat cheese, baked & fried goods
Choose wisely from many available food products

36. From Guidelines to Groceries
Fat replacers
Ingredients derived from CHO, pro, or fat
Replace fat in foods
Artificial fats offer sensory and cooking qualities but no kcalories.
Research on olestra supports its safety but it decreases the absorption of fat-soluble vits and may cause digestive distress in some
Read food labels
Total fat, saturated fat, trans fat, and cholesterol
Compare products
% Daily Value vs. % kcalories from fat