chapter5

The Lipids: The Lipids: Triglycerides, Triglycerides,

Phospholipids, and Phospholipids, and SterolsSterols

Chapter 5Chapter 5

IntroductionIntroduction

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

• Family of lipids• Triglycerides• Phospholipids• Sterols

ChemistChemist’’s View of Fatty Acids s View of Fatty Acids and Triglyceridesand 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

ChemistChemist’’s View of Fatty Acids s View of Fatty Acids and Triglyceridesand 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

18-Carbon Fatty Acids

ChemistChemist’’s View of Fatty Acids s View of Fatty Acids and Triglyceridesand Triglycerides

• Fatty acids• Location of double bonds

• Nearest the methyl end of the carbon chain

• Omega number

• Linolenic acid• Monounsaturated fatty acids

• Omega-9 groups

Omega-3 and Omega-6 Fatty Acids Compared

ChemistChemist’’s View of Fatty Acids s View of Fatty Acids and Triglyceridesand Triglycerides

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

condensation reactions• Usually contain mixture

of fatty acids

Condensation of Glycerol and Condensation of Glycerol and Fatty Acids to Form a TriglycerideFatty Acids to Form a Triglyceride

ChemistChemist’’s View of Fatty Acids s View of Fatty Acids and Triglyceridesand Triglycerides

• Characteristics of solid fats and oils• Firmness

• Polyunsaturated fats

• Saturated fats

• Length of carbon chain

• Stability • Oxidation and spoilage of fats

Diagram of Saturated & Unsaturated Fatty Acids Compared

Fatty Acid Composition of Common Food Fats

ChemistChemist’’s View of Fatty Acids s View of Fatty Acids and Triglyceridesand Triglycerides

• Characteristics of solid fats and oils• Hydrogenation

• Advantages

• Trans-fatty acids• Configurations – cis and trans

• Similarity to other types of fat

HydrogenationHydrogenation

Cis- and Cis- and TransTrans-Fatty Acids -Fatty Acids ComparedCompared

ChemistChemist’’s View of s View of Phospholipids and SterolsPhospholipids and Sterols

• Phospholipids• Solubility in fat and water• Emulsifiers in food industry• Lecithin• Food sources• Roles

• Part of cell membranes

• Emulsifiers

Lecithin

ChemistChemist’’s View of s View of Phospholipids and SterolsPhospholipids and Sterols

• Sterols• Food sources

• Cholesterol

• Plant sterols

• Roles of sterols• Body compounds made

from cholesterol

Lipid DigestionLipid Digestion

• Fats are hydrophobic• Digestive enzymes are hydrophilic

• Goal of fat digestion• Dismantle triglycerides

• Monoglycerides, fatty acids, and glycerol

Lipid DigestionLipid Digestion

• Mouth• Lingual lipase

• Stomach• Strong muscle contractions• Gastric lipase

Lipid DigestionLipid 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 TriglycerideHydrolysis of a Triglyceride

Enterohepatic CirculationEnterohepatic Circulation

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 AbsorptionLipid Absorption

• Directly into bloodstream• Glycerol and short- & medium-chain fatty

acids

• Lymphatic system• Micelles diffuse into intestinal cells• Reassembly of triglycerides• Packed with proteins – chylomicrons • Bypass liver at first

Absorption of FatAbsorption of Fat

Lipid TransportLipid Transport

• Four main types of lipoproteins• Chylomicrons

• Largest and least dense

• Transport diet-derived lipids

• Liver removes remnants from blood

• Very-low-density lipoproteins (VLDL)• Made in the liver

• Proportion of lipid shift

Lipid TransportLipid Transport

• Four main types of lipoproteins• Low-density lipoproteins (LDL)

• Cell needs

• Liver regulation

• High-density lipoproteins (HDL)• Remove cholesterol from cells

• Carry cholesterol to liver for recycling

• Anti-inflammatory properties

• Health implications

Sizes and Compositions of the Lipoproteins

Lipid Transport via Lipid Transport via LipoproteinsLipoproteins

Role of TriglyceridesRole of Triglycerides

• Provide the cells with energy• Virtually unlimited ability to store fat energy in

body

• Adipose tissue• Secretes hormones

• Adipokines

• Skin insulation, shock absorption, cell membranes, and cell signaling pathways

An Adipose Cell

Essential Fatty Acids

• Must be supplied by the diet• Linoleic acid• Linolenic acid

• Can be used to make other fatty acids

Essential Fatty AcidsEssential Fatty Acids

• Linoleic acid – Omega-6 fatty acid• Sources

• Linolenic acid – Omega-3 fatty acid• Sources • DHA • EPA

Essential Fatty Acids

• Eicosanoids • ‘Hormonelike”• Health benefits

• Omega-6 to Omega-3 ratio• Fatty acid deficiencies

• Symptoms

A Preview of Lipid MetabolismA Preview of Lipid Metabolism

• Adipose cells store fat after meals• Lipoprotein lipase

• Hydrolyzes triglycerides

• Triglycerides reassembled inside adipose cells

• Using fat for energy• Protein sparing• Energy deprivation

• Fasting and ketone bodies

Health Effects of Saturated Fats, Health Effects of Saturated Fats, Trans Trans Fats, and CholesterolFats, and Cholesterol

• Current American diet• Blood lipid profile• Heart disease

• Elevated blood cholesterol• Saturated fat – increase LDL cholesterol,

promote blood clotting

• Dietary choices

• Trans fats – increase LDL cholesterol

• Dietary cholesterol

Health Effects of Saturated Fats, Health Effects of Saturated Fats, Trans Trans Fats, and CholesterolFats, 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• Dietary recommendations

Recommended Intakes of Saturated Recommended Intakes of Saturated Fat, Fat, TransTrans Fat, & Cholesterol Fat, & Cholesterol

• DRI and Dietary Guidelines• Diet low in saturated and trans fat• Diet low in cholesterol• 20 to 35 percent of daily energy from fat

• Daily Values (DV) on food labels• Saturated fat and cholesterol

Health Effects of Monounsaturated Health Effects of Monounsaturated & Polyunsaturated Fats& 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

Replacing Saturated with Unsaturated Fat

Recommended Intakes of Recommended Intakes of Mono- & Polyunsaturated FatsMono- & 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 GroceriesFrom Guidelines to Groceries

• Fat-soluble vitamins• A, D, E, and K

• Flavor, texture, and palatability • Protein foods

• Selections

• Milk and milk products• Selections

Cutting Fat Cuts kCalories and Saturated Fat

From Guidelines to GroceriesFrom Guidelines to Groceries

• Vegetables, fruits, and grains• Lowers consumption of various fats in the

diet

• Solid fats and oils• Fried and baked goods

• Choose wisely• Unprocessed foods

From Guidelines to GroceriesFrom Guidelines to Groceries

• Read food labels• Total fat, saturated fat, trans fat, and

cholesterol• Compare products• % Daily Value vs. % kcalories from fat

• Fat replacers• Types• Risks

High-Fat Foods – High-Fat Foods – Friend or Foe?Friend or Foe?

Highlight 5Highlight 5

Guidelines for Fat IntakeGuidelines 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

High-Fat Foods and Heart High-Fat Foods and Heart HealthHealth

• Olive oil• Benefits for heart health• Replace saturated fats

• Nuts• LDL cholesterol• Fat composition• Benefits for heart health• Cautious advice for dietary inclusion

High-Fat Foods and Heart High-Fat Foods and Heart HealthHealth

• Fish• Omega-3 fatty acids

• Benefits for heart health

• Environmental contaminants• Dietary recommendations

High-Fat Foods and Heart High-Fat Foods and Heart DiseaseDisease

• 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

High-Fat Foods and Heart High-Fat Foods and Heart DiseaseDisease

High-Fat Foods and Heart High-Fat Foods and Heart DiseaseDisease