The Lipids: Triglycerides,

Phospholipids, and Sterols

Chapter 5

Objectives for Chapter 5

1. Recognize the chemistry of fatty acids and triglycerides and differences between saturated and unsaturated fats. 1. Describe the structure of a fatty acid and the effects of chain length and saturation on the properties of the fat.

2. Describe the triglyceride.

3. List and describe the three types of fatty acids found in foods.

4. Explain the structure of the omega-3 and -6 fatty acids.

2. Describe the chemistry, food sources, and roles of phospholipids and sterols.

3. Summarize fat digestion, absorption, and transport. 1. Trace the digestion of lipids including identification of enzymes needed and the role of bile.

2. Describe the absorption of lipids into the intestine and the formation of the chylomicron.

3. Describe the role of the liver in the production of lipoproteins.

4. Explain the health implications of LDL and HDL and the factors that raise or lower levels of these lipoproteins.

4. Outline the major roles of fats in the body, including a discussion of essential fatty acids and the omega fatty acids. 1. Identify the uses of triglyceride in the body.

2. Identify the essential fatty acids and their role in the formation of eicosanoids.

5. Explain the relationships among saturated fat, trans fat, and cholesterol and chronic diseases, noting recommendations.

6. Explain the relationships between monounsaturated and polyunsaturated fats and health, noting recommendations.

7. Identify which fats support health and which impair it.1. Name practical suggestions for food selections to replace saturated and trans fats with monounsaturated and

polyunsaturated fats.

Introduction

• Poor health• Too much fat• Too little fat• Too much of some kinds of fat

• Family of lipids• Triglycerides• Phospholipids• Sterols

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

Chemist’s View of Fatty Acids and Triglycerides

• Fatty acids• 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

COOHH3C

18-Carbon Fatty Acids

Yes, I will expect you to know this chart!

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

Omega-3 and Omega-6 Fatty Acids Compared

Chemist’s View of Fatty Acids and Triglycerides

• Triglycerides• Glycerol backbone• Three fatty acids• Formed via series of

condensation reactions• Usually contain mixture

of fatty acids

Condensation of Glycerol and Fatty Acids to Form a Triglyceride

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

Diagram of Saturated & Unsaturated Fatty Acids Compared

Fatty Acid Composition of Common Food Fats

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)

Hydrogenation

Cis- and Trans-Fatty Acids Compared

Chemist’s View of Phospholipids and Sterols

• Phospholipids• Solubility in fat and water• Emulsifiers in food industry

• Lecithin (most common)• Food sources

• Eggs, soybeans, peanuts• Roles

• Part of cell membranes• Emulsifiers

Lecithin

Chemist’s View of Phospholipids and Sterols

• Sterols• Food sources

• Cholesterol• Plant sterols

• Roles of sterols• Body compounds made

from cholesterol

• Bile acids, hormones, vitamin D, cholesterol

Lipid Digestion

• Fats are hydrophobic• Digestive enzymes are hydrophilic

• Goal of fat digestion• Dismantle triglycerides

• Monoglycerides, fatty acids, and glycerol

Lipid Digestion

• Mouth• Lingual lipase

• Stomach• Strong muscle contractions• Gastric lipase

Lipid Digestion

• Small intestine• Cholecystokinin (CCK)

• Gall bladder releases bile• Bile acts as emulsifier

• Pancreatic lipase• Hydrolysis

• Triglycerides and phospholipids• Bile routes

• Blood cholesterol levels

Fat

Watery GI juices

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.

Enzyme

Bile

Enzymes

Stepped Art

Emulsified fatEmulsified

fat

Figure 5-12 p140

Emulsified fat

Hydrolysis of a Triglyceride

In the gallbladder, bile is stored.

In the liver, bile is made from cholesterol.

In the colon, bile that has been trapped by soluble fibers is lost in feces.

In the small intestine, bile emulsifies fats.

Stepped Art

Figure 5-14 p141

Lipid Absorption

• Glycerol, short- & medium-chain fatty acids• Directly into bloodstream

• Monoglycerides, long-chain fatty acids• Lymphatic system

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

Absorption of Fat

Lipid Transport

• Transport of lipids through water-based blood requires transport vehicles

• Four main types of lipoproteins1. Chylomicrons

• Largest and least dense• Transport diet-derived lipids• Liver removes remnants from blood

Lipid Transport

• Four main types of lipoproteins2. Very-low-density lipoproteins (VLDL)

• Made in the liver• Proportion of lipid shift as cells remove

triglycerides3. Low-density lipoproteins (LDL)

• Cells use for energy, make hormones, new membranes

• Liver regulation – special receptors to get LDL out of circulation

Lipid Transport

• Four main types of lipoproteins4. 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

Sizes and Compositions of the Lipoproteins

Lipid Transport via Lipoproteins

Role of Triglycerides

• Provide the cells with energy• 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

An Adipose Cell

• Must be supplied by the diet• Linoleic acid (Ω6)• Linolenic acid (Ω3)

• Can be used to make other fatty acids

Essential Fatty Acids

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

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

Essential Fatty Acids

• Ω 6: Ω3 ratio• 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

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

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

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

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

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

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

Replacing Saturated with Unsaturated Fat

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 – 0.6-1.2% of daily energy

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

Cutting Fat Cuts kCalories and Saturated Fat

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

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

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