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1、LIPIDSLearning Objectives:Understand lipid terminology and classificationsUnderstand the digestion and absorption of lipidsLearn about the function of lipids in the diet, and how they relate to health issuesWHAT ARE THE LIPIDS?A broad range of organic compounds that dissolve easily in organic solven

2、ts, but range in their solubility in waterHydrophobic “water-fearingLipophilic “fat-lovingCLASSES of LIPIDSSIMPLE LIPIDSFatty AcidsTriglyceridesWaxesCOMPOUND LIPIDSPhospholipidsDERIVED LIPIDSSterols FATTY ACIDSKey building blocks for lipidsChains of carbon atoms with a carboxyl group at one end, and

3、 a methyl group at the otherMay be “free or attached to another compoundDetermine the characteristics of the fatFATTY ACIDSCHAIN LENGTHShort chain = less than 6 carbonsMedium chain = 6-10 carbonsLong chain = 12 or more carbonsThe shorter the carbon chain, the more liquid the fatty acid isFATTY ACIDS

4、SATURATIONSATURATED FATTY ACID =If all the carbon atoms in the chain are joined with single bonds, and the remaining bonds are attached to hydrogenFATTY ACIDSSATURATIONUNSATURATED FATTY ACID = If adjoining carbons are joined by double bondsFATTY ACIDSUNSATURATEDOne double bond = monounsaturated fatt

5、y acidTwo or more double bonds = poly- unsaturated fatty acidLong-chain saturated fatty acids stack tightly and form solids at room temperatureMonounsaturated and polyunsaturated fatty acids dont stack compactly and are liquid at room temperatureShort-chain saturated fatty acids are also liquid at r

6、oom temperatureFigure 5.6FATTY ACIDSFATTY ACIDSTWO TYPES OF BOND FORMATION:CIS - hydrogens on the carbons joined by a double bond are on the same side = the carbon chain is bentTRANS hydrogens on the carbons joined by a double bond are on the opposite side = the carbon chain is straighterFATTY ACIDS

7、Omega-3 Fatty Acid double bond at carbon 3 Omega-6 Fatty Acid double bond at carbon 6 Omega-9 Fatty Acid double bond at carbon 9 *count carbons from the methyl (omega) endOmega 3Omega 6Omega 9FATTY ACIDSNOMENCLATUREAlpha and Omega18:0, 18:1, etc.FATTY ACIDSNonessential Fatty Acids our body can make

8、certain fatty acids so they are not required in the dietEssential Fatty Acids our bodies cannot make C-C double bonds before the 9th carbon from the methyl end, so we must get these fatty acids from our dietEFAS = omega-6 linoleic acid & omega-3 alpha-linolenic acidFATTY ACIDSOmega-3: Alpha-Linoleni

9、c Acid (ALA), Eicosapentaenoic Acid (EPA), Docosahexaenoic Acid (DHA)Omega-6: Linoleic Acid, Arachidonic Acid Sources of Omega-3 Fatty AcidsFlaxseed, soybean oil, walnuts, some leafy dark green vegetables (ALA)Fatty fish: salmon, tuna, and mackerel, fish oils (EPA and DHA)Sources of Omega-6 Fatty Ac

10、idsSeeds, nuts, common vegetable oils: corn, safflower, cottonseed, sunflower seed, peanut (linoleic acid)Meat (arachidonic acid)FATTY ACIDSEICOSANOIDSA small percentage of fatty acids become eicosanoidsThey contain 20 or more carbons and are important in the inflammatory process, blood vessel dilat

11、ion and constriction, and blood clottingEICOSANOIDSOmega-6sLinoleic acid is converted to arachidonic acid and eicosanoids are formed.Overall effect: constricting blood vessels, promoting inflammation and blood clottingEICOSANOIDS Omega-3sAlpha-linolenic acid is converted to eicosapentanoic acid (EPA

12、) and docosahexanoic acid (DHA) and eicosanoids are formedOverall effect: dilating blood vessels, discouraging blood clotting, and reducing inflammationTRIGLYCERIDESSTRUCTURETriglyceride - three fatty acids attached to a glycerol backbone Diglyceride two fatty acids +glycerolMonoglyceride one fatty

13、acid +glycerolTriglycerideFatty AcidsTRIGLYCERIDESFUNCTIONSMajor lipid in the body and dietStored fat provides about 60% of the bodys resting energy needs compactly!Insulation and protectionCarrier of fat-soluble compoundsSensory qualities flavor and textureCompound Lipids: PHOSPHOLIPIDSContain a gl

14、ycerol bonded to two fatty acidsThe phosphate group is hydrophilic while the fatty acids groups are lipophilicBecause of this structure, phospholipids are ideal emulsifiers, and the perfect structure for cell membranesFunctionsCell MembranesPhosholipids are the major component of cell membranesFatty

15、 acids, choline, as well as other substances are bound in the phospholipid layerLipid TransportIn the stomachIn the intestineIn the bloodstream, and the lymphatic system Protein ChannelHydrophilicHydrophobicHydrophilicFunctions EmulsifiersLecithins are used by the food industry to:Combine foods that

16、 wouldnt normally mixIncrease dispersion and reduce fat separationIncrease shelf-life, prolong flavor release, and prevent such products as gum from sticking to teethPhospholipids in FoodsA typical diet contains only about 2 grams per dayLecithin (phosphatidylcholine) is the major phospholipid and i

17、s found in:Liver, egg yolk, soybeans, peanuts, legumes, spinach, and wheat germUsually lost during food processingDerived Lipids: STEROLSSterols are hydrocarbons with a multiple ring structureThey are hydrophobic and lipophilicContain no fatty acidsCholesterol is the best-known sterol, found only in

18、 animal productsCHOLESTEROL: FunctionsMajor component of cell membranes (especially abundant in nerve and brain tissue)Precursor molecule: Example - Vitamin D and estrogen are synthesized from cholesterolImportant in the synthesis of bile acids CHOLESTEROL: SynthesisThe liver manufactures most of th

19、e cholesterol in our bodiesThe intestine and all cells contribute a small amountOverall, the body produces about 1000 mg per daySerum cholesterol levels are homeostatically controlled (set-point)DIGESTIONMouth: chewing, lingual lipase, and dietary phospholipidsStomach: gastric lipaseSmall Intestine:

20、 CCK = bile, Secretin = pancreatic juice (pancreatic lipase)Micelles: tiny emulsified fat packets that can enter intestinal cells (enterocytes)DIGESTIBILITYAbnormal to find more than 6 or 7% of ingested lipids still intact in the fecesSteatorrhea indicates fat malabsorptionBreast milkMedium-Chain Tr

21、igylceridesShort-Chain Fatty Acids ABSORPTIONMost fat absorption takes place in the duodenum or jejunum micelles carry monoglycerides and free fatty acids to the brush border where they diffuse into enterocytes Bile salts are absorbed in the ileum (enterohepatic circulation)Once in the enterocytes,

22、monoglycerides and free fatty acids are reformed into triglyceridesThe triglycerides, cholesterol, phospholipids, and protein carriers form LIPOPROTEINABSORPTIONOnce these lipoproteins leave the cell, they become CHYLOMICRONS and enter the lymph systemMCTs, short-chain fatty acids and glycerol are a

23、bsorbed directly into bloodstream. They do not enter the lymph system.Cholesterol and other sterols are poorly absorbed. Overall, about 50% of dietary cholesterol is absorbed.Dietary fat increases cholesterol absorptionFiber (especially soluble fiber) and phytosterols decrease cholesterol absorption

24、triglyceridesLipids in the BodyChylomicronsVery-Low-Density LipoproteinIntermediate-Density LipoproteinLow-Density LipoproteinHigh-Density Lipoprotein Chylomicrons are lipoproteinsHeart DiseaseMore than 58 million Americans have at least one form of CVD stroke, hypertension, or coronary heart diseas

25、e1 in 9 women, and 1 in 6 men aged 45-64 years of age have some form of heart diseaseMyocardial Infarction (heart attack) is the leading cause of death in American men and womenAtherosclerosisA slow, progressive disease that begins in childhood and takes decades to advance. Basically, plaque (lipid

26、deposits and other substances) forms in response to injuries on the artery wallPlaque can eventually completely occlude the artery leading to MIInjury can be caused by: hypercholesterolemia, oxidized LDL, hypertension, smoking, diabetes, homocysteine, and diets high in saturated fat What Are the Lip

27、id Related Risk Factors for CVD?High LDL Cholesterol and Low HDL CholesterolA diet high in cholesterolA diet high in saturated fatA diet high in trans-fatty acidsTrans Fatty AcidsTrans fatty acids tend to raise total blood cholesterol levels, but less than more saturated fatty acidsTrans fatty acids also tend to raise LDL cholesterol and lower HDL cholesterol It is not clear if trans fats that occur naturally have the same effect a