LIPIDSLIPIDS

Learning Objectives:Learning Objectives:• Understand lipid terminology and Understand lipid terminology and

classificationsclassifications• Understand the digestion and Understand the digestion and

absorption of lipidsabsorption of lipids• Learn about the function of lipids in Learn about the function of lipids in

the diet, and how they relate to health the diet, and how they relate to health issuesissues

WHAT ARE THE LIPIDS?WHAT ARE THE LIPIDS?

• A broad range of organic compounds A broad range of organic compounds that dissolve easily in organic solvents, that dissolve easily in organic solvents, but range in their solubility in waterbut range in their solubility in water

• Hydrophobic – “water-fearing”Hydrophobic – “water-fearing”• Lipophilic – “fat-loving”Lipophilic – “fat-loving”

CLASSES of LIPIDSCLASSES of LIPIDS

SIMPLE LIPIDSSIMPLE LIPIDS• Fatty AcidsFatty Acids• TriglyceridesTriglycerides• WaxesWaxes

COMPOUND LIPIDSCOMPOUND LIPIDS• PhospholipidsPhospholipids

DERIVED LIPIDSDERIVED LIPIDS• Sterols Sterols

FATTY ACIDSFATTY ACIDS

• Key building blocks for lipidsKey building blocks for lipids• Chains of carbon atoms with a carboxyl Chains of carbon atoms with a carboxyl

group at one end, and a methyl group at group at one end, and a methyl group at the otherthe other

• May be “free” or attached to another May be “free” or attached to another compoundcompound

• Determine the characteristics of the fatDetermine the characteristics of the fat

FATTY ACIDSFATTY ACIDS

CHAIN LENGTHCHAIN LENGTH• Short chain = less than 6 carbonsShort chain = less than 6 carbons• Medium chain = 6-10 carbonsMedium chain = 6-10 carbons• Long chain = 12 or more carbonsLong chain = 12 or more carbons• The shorter the carbon chain, the more The shorter the carbon chain, the more

liquid the fatty acid isliquid the fatty acid is

FATTY ACIDSFATTY ACIDS

SATURATIONSATURATION• SATURATED FATTY ACID =If all the SATURATED FATTY ACID =If all the

carbon atoms in the chain are joined carbon atoms in the chain are joined with single bonds, and the remaining with single bonds, and the remaining bonds are attached to hydrogenbonds are attached to hydrogen

FATTY ACIDSFATTY ACIDS

SATURATIONSATURATION• UNSATURATED FATTY ACID = If UNSATURATED FATTY ACID = If

adjoining carbons are joined by double adjoining carbons are joined by double bondsbonds

FATTY ACIDSFATTY ACIDS

UNSATURATEDUNSATURATED• One double bond = monounsaturated fatty One double bond = monounsaturated fatty

acidacid• Two or more double bonds = poly-Two or more double bonds = poly-

unsaturated fatty acidunsaturated fatty acid

• Long-chain saturated fatty acids stack Long-chain saturated fatty acids stack tightly and form solids at room temperaturetightly and form solids at room temperature

• Monounsaturated and polyunsaturated fatty Monounsaturated and polyunsaturated fatty acids don’t stack compactly and are liquid acids don’t stack compactly and are liquid at room temperatureat room temperature

• Short-chain saturated fatty acids are also Short-chain saturated fatty acids are also liquid at room temperatureliquid at room temperature

• Figure 5.6Figure 5.6

FATTY ACIDSFATTY ACIDS

FATTY ACIDSFATTY ACIDS

TWO TYPES OF BOND FORMATION:TWO TYPES OF BOND FORMATION:• CIS - hydrogens on the carbons joined by CIS - hydrogens on the carbons joined by

a double bond are on the same side = the a double bond are on the same side = the carbon chain is bentcarbon chain is bent

• TRANS – hydrogens on the carbons TRANS – hydrogens on the carbons joined by a double bond are on the joined by a double bond are on the opposite side = the carbon chain is opposite side = the carbon chain is straighterstraighter

FATTY ACIDSFATTY ACIDS

• Omega-3 Fatty Acid – double bond at Omega-3 Fatty Acid – double bond at carbon 3 carbon 3

• Omega-6 Fatty Acid – double bond at Omega-6 Fatty Acid – double bond at carbon 6 carbon 6

• Omega-9 Fatty Acid – double bond at Omega-9 Fatty Acid – double bond at carbon 9 carbon 9

• *count carbons from the methyl (omega) *count carbons from the methyl (omega) endend

Omega 3Omega 3

Omega 6Omega 6

Omega 9Omega 9

FATTY ACIDSFATTY ACIDS

NOMENCLATURENOMENCLATURE• Alpha and OmegaAlpha and Omega• 18:0, 18:1, etc.18:0, 18:1, etc.

FATTY ACIDSFATTY ACIDS• Nonessential Fatty Acids – our body can Nonessential Fatty Acids – our body can

make certain fatty acids so they are not make certain fatty acids so they are not required in the dietrequired in the diet

• Essential Fatty Acids – our bodies cannot Essential Fatty Acids – our bodies cannot make C-C double bonds before the 9make C-C double bonds before the 9thth carbon from the methyl end, so we must carbon from the methyl end, so we must get these fatty acids from our dietget these fatty acids from our diet

• EFAS = omega-6 linoleic acid & omega-3 EFAS = omega-6 linoleic acid & omega-3 alpha-linolenic acidalpha-linolenic acid

FATTY ACIDSFATTY ACIDS

• Omega-3: Alpha-Linolenic Acid Omega-3: Alpha-Linolenic Acid (ALA), Eicosapentaenoic Acid (EPA), (ALA), Eicosapentaenoic Acid (EPA), Docosahexaenoic Acid (DHA)Docosahexaenoic Acid (DHA)

• Omega-6: Linoleic Acid, Arachidonic Omega-6: Linoleic Acid, Arachidonic Acid Acid

Sources of Omega-3 Sources of Omega-3 Fatty AcidsFatty Acids

• Flaxseed, soybean oil, walnuts, Flaxseed, soybean oil, walnuts, some leafy dark green some leafy dark green vegetables (ALA)vegetables (ALA)

• Fatty fish: salmon, tuna, and Fatty fish: salmon, tuna, and mackerel, fish oils (EPA and mackerel, fish oils (EPA and DHA)DHA)

Sources of Omega-6 Sources of Omega-6 Fatty AcidsFatty Acids

• Seeds, nuts, common Seeds, nuts, common vegetable oils: corn, safflower, vegetable oils: corn, safflower, cottonseed, sunflower seed, cottonseed, sunflower seed, peanut (linoleic acid)peanut (linoleic acid)

• Meat (arachidonic acid)Meat (arachidonic acid)

FATTY ACIDSFATTY ACIDS

EICOSANOIDSEICOSANOIDS• A small percentage of fatty acids A small percentage of fatty acids

become eicosanoidsbecome eicosanoids• They contain 20 or more carbons They contain 20 or more carbons

and are important in the and are important in the inflammatory process, blood vessel inflammatory process, blood vessel dilation and constriction, and blood dilation and constriction, and blood clottingclotting

EICOSANOIDSEICOSANOIDS

Omega-6sOmega-6s• Linoleic acid is converted to Linoleic acid is converted to

arachidonic acid and arachidonic acid and eicosanoids are formed.eicosanoids are formed.

• Overall effect: constricting blood Overall effect: constricting blood vessels, promoting vessels, promoting inflammation and blood clottinginflammation and blood clotting

EICOSANOIDS EICOSANOIDS

Omega-3sOmega-3s• Alpha-linolenic acid is converted to Alpha-linolenic acid is converted to

eicosapentanoic acid (EPA) and eicosapentanoic acid (EPA) and docosahexanoic acid (DHA) and docosahexanoic acid (DHA) and eicosanoids are formedeicosanoids are formed

• Overall effect: dilating blood Overall effect: dilating blood vessels, discouraging blood vessels, discouraging blood clotting, and reducing inflammationclotting, and reducing inflammation

TRIGLYCERIDESTRIGLYCERIDES

STRUCTURESTRUCTURE• Triglyceride - three fatty acids Triglyceride - three fatty acids

attached to a glycerol backbone attached to a glycerol backbone • Diglyceride – two fatty acids +glycerolDiglyceride – two fatty acids +glycerol• Monoglyceride – one fatty acid Monoglyceride – one fatty acid

+glycerol+glycerol

TriglycerideFatty Acids

TRIGLYCERIDESTRIGLYCERIDES

FUNCTIONSFUNCTIONS• Major lipid in the body and dietMajor lipid in the body and diet• Stored fat provides about 60% of the Stored fat provides about 60% of the

body’s resting energy needs – body’s resting energy needs – compactly!compactly!

• Insulation and protectionInsulation and protection• Carrier of fat-soluble compoundsCarrier of fat-soluble compounds• Sensory qualities – flavor and textureSensory qualities – flavor and texture

Compound Lipids: Compound Lipids: PHOSPHOLIPIDSPHOSPHOLIPIDS

• Contain a glycerol bonded to two fatty Contain a glycerol bonded to two fatty acidsacids

• The phosphate group is hydrophilic while The phosphate group is hydrophilic while the fatty acids groups are lipophilicthe fatty acids groups are lipophilic

• Because of this structure, phospholipids Because of this structure, phospholipids are ideal emulsifiers, and the perfect are ideal emulsifiers, and the perfect structure for cell membranesstructure for cell membranes

FunctionsFunctions

Cell MembranesCell Membranes• Phosholipids are the major component of cell Phosholipids are the major component of cell

membranesmembranes• Fatty acids, choline, as well as other substances Fatty acids, choline, as well as other substances

are bound in the phospholipid layerare bound in the phospholipid layer

Lipid TransportLipid Transport• In the stomachIn the stomach• In the intestineIn the intestine• In the bloodstream, and the lymphatic system In the bloodstream, and the lymphatic system

Protein Protein ChannelChannel

HydrophilicHydrophilic

HydrophobicHydrophobic

HydrophilicHydrophilic

FunctionsFunctions

EmulsifiersEmulsifiers

Lecithins are used by the food industry to:Lecithins are used by the food industry to:• Combine foods that wouldn’t normally mixCombine foods that wouldn’t normally mix• Increase dispersion and reduce fat Increase dispersion and reduce fat

separationseparation• Increase shelf-life, prolong flavor release, Increase shelf-life, prolong flavor release,

and prevent such products as gum from and prevent such products as gum from sticking to teethsticking to teeth

Phospholipids in FoodsPhospholipids in Foods

• A typical diet contains only about 2 grams A typical diet contains only about 2 grams per dayper day

• Lecithin (phosphatidylcholine) is the major Lecithin (phosphatidylcholine) is the major phospholipid and is found in:phospholipid and is found in:

• Liver, egg yolk, soybeans, peanuts, Liver, egg yolk, soybeans, peanuts, legumes, spinach, and wheat germlegumes, spinach, and wheat germ

• Usually lost during food processingUsually lost during food processing

Derived Lipids: STEROLSDerived Lipids: STEROLS

• Sterols are hydrocarbons with a multiple Sterols are hydrocarbons with a multiple ring structurering structure

• They are hydrophobic and lipophilicThey are hydrophobic and lipophilic• Contain no fatty acidsContain no fatty acids• Cholesterol is the best-known sterol, Cholesterol is the best-known sterol,

found only in animal productsfound only in animal products

CHOLESTEROL: FunctionsCHOLESTEROL: Functions

• Major component of cell membranes Major component of cell membranes (especially abundant in nerve and brain (especially abundant in nerve and brain tissue)tissue)

• Precursor molecule: Example - Vitamin D Precursor molecule: Example - Vitamin D and estrogen are synthesized from and estrogen are synthesized from cholesterolcholesterol

• Important in the synthesis of bile acidsImportant in the synthesis of bile acids

CHOLESTEROL: SynthesisCHOLESTEROL: Synthesis

• The liver manufactures most of the The liver manufactures most of the cholesterol in our bodiescholesterol in our bodies

• The intestine and all cells contribute a The intestine and all cells contribute a small amountsmall amount

• Overall, the body produces about 1000 mg Overall, the body produces about 1000 mg per dayper day

• Serum cholesterol levels are Serum cholesterol levels are homeostatically controlled (set-point)homeostatically controlled (set-point)

DIGESTIONDIGESTION

• Mouth: chewing, lingual lipase, and dietary Mouth: chewing, lingual lipase, and dietary phospholipidsphospholipids

• Stomach: gastric lipaseStomach: gastric lipase• Small Intestine: CCK = bile, Secretin = Small Intestine: CCK = bile, Secretin =

pancreatic juice (pancreatic lipase)pancreatic juice (pancreatic lipase)• Micelles: tiny emulsified fat packets that Micelles: tiny emulsified fat packets that

can enter intestinal cells (enterocytes)can enter intestinal cells (enterocytes)

DIGESTIBILITYDIGESTIBILITY

• Abnormal to find more than 6 or 7% of Abnormal to find more than 6 or 7% of ingested lipids still intact in the fecesingested lipids still intact in the feces

• Steatorrhea indicates fat malabsorptionSteatorrhea indicates fat malabsorption• Breast milkBreast milk• Medium-Chain TrigylceridesMedium-Chain Trigylcerides• Short-Chain Fatty AcidsShort-Chain Fatty Acids

ABSORPTIONABSORPTION

• Most fat absorption takes place in the duodenum Most fat absorption takes place in the duodenum or jejunum – micelles carry monoglycerides and or jejunum – micelles carry monoglycerides and free fatty acids to the brush border where they free fatty acids to the brush border where they diffuse into enterocytes diffuse into enterocytes

• Bile salts are absorbed in the ileum (enterohepatic Bile salts are absorbed in the ileum (enterohepatic circulation)circulation)

• Once in the enterocytes, monoglycerides and Once in the enterocytes, monoglycerides and free fatty acids are reformed into triglyceridesfree fatty acids are reformed into triglycerides

• The triglycerides, cholesterol, phospholipids, and The triglycerides, cholesterol, phospholipids, and protein carriers form LIPOPROTEINprotein carriers form LIPOPROTEIN

ABSORPTIONABSORPTION

• Once these lipoproteins leave the cell, they become Once these lipoproteins leave the cell, they become CHYLOMICRONS and enter the lymph systemCHYLOMICRONS and enter the lymph system

• MCTs, short-chain fatty acids and glycerol are MCTs, short-chain fatty acids and glycerol are absorbed directly into bloodstream. They do not absorbed directly into bloodstream. They do not enter the lymph system.enter the lymph system.

• Cholesterol and other sterols are poorly Cholesterol and other sterols are poorly absorbed. Overall, about 50% of dietary absorbed. Overall, about 50% of dietary cholesterol is absorbed.cholesterol is absorbed.

• Dietary fat increases cholesterol absorptionDietary fat increases cholesterol absorption• Fiber (especially soluble fiber) and phytosterols Fiber (especially soluble fiber) and phytosterols

decrease cholesterol absorptiondecrease cholesterol absorption

triglycerides

Lipids in the BodyLipids in the Body

• ChylomicronsChylomicrons• Very-Low-Density LipoproteinVery-Low-Density Lipoprotein• Intermediate-Density LipoproteinIntermediate-Density Lipoprotein• Low-Density LipoproteinLow-Density Lipoprotein• High-Density Lipoprotein High-Density Lipoprotein

Chylomicrons are lipoproteinsChylomicrons are lipoproteins

Heart DiseaseHeart Disease

• More than 58 million Americans have at More than 58 million Americans have at least one form of CVD – stroke, least one form of CVD – stroke, hypertension, or coronary heart diseasehypertension, or coronary heart disease

• 1 in 9 women, and 1 in 6 men aged 45-64 1 in 9 women, and 1 in 6 men aged 45-64 years of age have some form of heart years of age have some form of heart diseasedisease

• Myocardial Infarction (heart attack) is the Myocardial Infarction (heart attack) is the leading cause of death in American men leading cause of death in American men and womenand women

AtherosclerosisAtherosclerosis

• A slow, progressive disease that begins in A slow, progressive disease that begins in childhood and takes decades to advance. childhood and takes decades to advance.

• Basically, plaque (lipid deposits and other Basically, plaque (lipid deposits and other substances) forms in response to injuries on the substances) forms in response to injuries on the artery wallartery wall

• Plaque can eventually completely occlude the Plaque can eventually completely occlude the artery leading to MIartery leading to MI

• Injury can be caused by: hypercholesterolemia, Injury can be caused by: hypercholesterolemia, oxidized LDL, hypertension, smoking, diabetes, oxidized LDL, hypertension, smoking, diabetes, homocysteine, and diets high in saturated fat homocysteine, and diets high in saturated fat

What Are the Lipid Related Risk What Are the Lipid Related Risk Factors for CVD?Factors for CVD?

• High LDL Cholesterol and Low HDL High LDL Cholesterol and Low HDL CholesterolCholesterol

• A diet high in cholesterolA diet high in cholesterol• A diet high in saturated fatA diet high in saturated fat• A diet high in trans-fatty acidsA diet high in trans-fatty acids

Trans Fatty AcidsTrans Fatty Acids

• Trans fatty acids tend to raise total blood Trans fatty acids tend to raise total blood cholesterol levels, but less than more saturated cholesterol levels, but less than more saturated fatty acidsfatty acids

• Trans fatty acids also tend to raise LDL Trans fatty acids also tend to raise LDL cholesterol and lower HDL cholesterol cholesterol and lower HDL cholesterol

• It is not clear if trans fats that occur naturally It is not clear if trans fats that occur naturally have the same effect as those produced by have the same effect as those produced by hydrogenating vegetable oilshydrogenating vegetable oils

• The Food and Drug Administration (FDA) has The Food and Drug Administration (FDA) has proposed that the amount of trans fatty acids in proposed that the amount of trans fatty acids in a food be included in the Nutrition Facts panela food be included in the Nutrition Facts panel

Ingredients: enriched wheat flour, corn Ingredients: enriched wheat flour, corn syrup, whole oats, raspberry preserves, syrup, whole oats, raspberry preserves, sugar, sugar, partially hydrogenated soybean partially hydrogenated soybean and/or cottonseed oiland/or cottonseed oil, glycerin, , glycerin, maltodextrin, honey, dextrose, natural and maltodextrin, honey, dextrose, natural and artificial flavors, nonfat dry milk, sodium artificial flavors, nonfat dry milk, sodium alginate, wheat bran, modified corn starch, alginate, wheat bran, modified corn starch, salt, cellulose gum, potassium salt, cellulose gum, potassium bicarbonate, lecithin, citric acid, xanthan bicarbonate, lecithin, citric acid, xanthan gum, calcium phosphate, malic acid, whey gum, calcium phosphate, malic acid, whey protein concentrate, red #40, blue #1. protein concentrate, red #40, blue #1.

Other Dietary ConsiderationsOther Dietary Considerations

• Homocysteine – high levels of this amino Homocysteine – high levels of this amino acid may promote atherosclerosis, acid may promote atherosclerosis, excessive blood clotting, or blood vessel excessive blood clotting, or blood vessel rigidityrigidity

• Omega-3 Fatty AcidsOmega-3 Fatty Acids• Soluble FiberSoluble Fiber• Antioxidants – clean up free-radicals Antioxidants – clean up free-radicals

(Vitamin E, Vitamin C, etc)(Vitamin E, Vitamin C, etc)• Other Phytochemicals – isoflavones and Other Phytochemicals – isoflavones and

lignanslignans