Y khoa, dược - Chapter 5: Lipids: not just fat

Chapter 5 Lipids: Not Just FatWhat Are Lipids?Essential nutrientsProvide energyHelp transport fat-soluble nutrients throughout the bodyContribute greatly to the flavor and texture of foodLipids IncludeTriglycerides (most abundant lipids)In body: stored in adipose tissueIn food: “fats and oils” Phospholipids (~2% of dietary lipids)Plant and animal originBody can make themSoluble in fat and waterSterols (very, very small % of lipids)Most well known: CholesterolFatty Acids Are Key Building BlocksFatty acidDetermines whether a fat is solid or liquid at room temperatureBasic structure: (-COOH); (-CH3)Fatty Acids Are Key Building BlocksChain lengthFatty acids differ in chain lengthLengths vary from 4 to 24 carbonsGrouped as short-chain, medium-chain, and long-chainFatty Acids Are Key Building BlocksChain LengthShorter fatty acids remain liquid at room temperature and even with refrigerationShorter fatty acids also are more water-solubleFatty Acids Are Key Building BlocksSaturationSaturated fatty acidsAll single bonds between carbonsUnsaturated fatty acidsOne or more carbon bonds is a double bondMonounsaturated fatty acid (MUFA)Polyunsaturated fatty acid (PUFA)Fats with more double bonds are generally more liquidyFatty Acids Are Key Building BlocksCis vs. transUnsaturated fatty acids can vary in shapeCis fatty acids Chain is bentOccur naturallyTrans fatty acidsChain is straighterProduced by hydrogenationTrans FatIn health, trans fatty acids are known to raise LDL (“bad”) cholesterol, and lower HDL (“good cholesterol”), promote systemic inflammation, and increase triglycerides in your blood.History and how it is made:In Europe (1910): needed a cheaper butter substitute for soldiersIn US (1960s): People wanted to eat a “healthier and cheaper butter”  food scientists decided to hydrogenate vegetable oil to solidify themFatty Acids are Key Building BlocksNonessential and essential fatty acidsNonessential fatty acidsCan be made in the bodyNot “essential” to have in your dietFatty Acids Are Key Building BlocksEssential and Nonessential Fatty AcidsEssential fatty acidsMust come from foodCannot be made by the bodyTwo families:Omega-3 (alpha-linolenic acid)Omega-6 (linoleic acid)Pre-cursors to eicosanoidsTriglyceridesStructureGlycerol + 3 fatty acidsMost fatty acids exist as part of triglyceride moleculesTriglyceridesFunctionsEnergy source: 9 kcal/gEnergy reserve: form of stored energy in adipose tissue Insulation and protection: Visceral fat Subcutaneous fat Carrier of fat-soluble nutrientsSensory qualities (flavor, odor, texture) in foodTriglyceridesFunctionsCarrier of Fat-Soluble CompoundsImproves intestinal absorption and bioavailability during digestionSensory QualitiesContributes to food’s flavor, odor, and textureTriglycerides in FoodFound in a variety of fats and oilsClassified by their most prevalent typeTriglycerides in FoodCommercial processing of fatsReduces waste, prevents spoilage, increases availability of calorie-rich oilsRemoves damaging free fatty acidsAdds antioxidants to delay rancidity and extend shelf lifeTriglycerides in FoodCommercial processing of fatsNegativesRemoves potentially healthful phospholipids, plant sterols, and other phytochemicalsFurther processing into solid fats increases the proportion of trans fatty acidsPhospholipidsStructureGlycerol + two fatty acids + phosphate groupCompatible with both fat and waterPhospholipidsFunctionsIdeal emulsifiersKeep fat suspended in waterKeep oil and water mixedPerfect structural element for cell membranesAble to communicate with watery environments of blood and cell fluidsAllows other lipids to enter and exit cellsPhospholipidsCell membranesDouble layer of phospholipidsSelectively allow both fatty and water-soluble substances into the cellStore fatty acids temporarilyPlays an important role in nerve cellsPhospholipidsLipid TransportIn the stomachBreak fats into tiny particles for digestionIn the intestineContinue emulsifying fatIn the bloodCoat the surface of the lipoproteins that carry lipid particles to their destinations in the bodyPhospholipidsEmulsifiers (lecithin)Lecithin used as an emulsifier to combine two ingredients that don’t ordinarily mix, such as oil and waterAllows ingredients in salad dressing to mix well and remain mixed, for examplePhospholipids in FoodOccur naturally in plants and animals, but in much smaller amounts than triglyceridesAbundant in egg yolks, liver, soybeans, peanutsNot a dietary essentialSterolsHave a multiple-ring structureBest known example is cholesterolMost contain no fatty acidSterolsCholesterol FunctionsMajor structural component of all cell membranesPrecursor of important substances, includingVitamin DSterol hormonesBile saltsSterolsCholesterol SynthesisPrimarily made in the liverSterols in FoodFound only in foods of animal originTypical American consumers between 250-700 mg of cholesterol and 250 milligrams of plant sterols per dayLipid Digestion and AbsorptionDigestion of Triglycerides and PhospholipidsMouthChewing and lingual lipase start digestionStomachBreaks triglycerides down to diglycerides and free fatty acidsSmall intestineBile and pancreatic lipase emulsify and break down the fats for absorptionIntestinal cells absorb glycerol and fatty acids into the bloodstreamLipid Digestion and AbsorptionLipid absorptionMicellesWater-soluble globules with a fatty coreCarry monoglycerides and long-chain fatty acids to microvilliBile recycling pathway known as enterohepatic circulationLipid Digestion and AbsorptionLipid absorptionLipoproteinCylomicronDeliver dietary lipids from intestines to cells and liverLipid Digestion and AbsorptionDigestion and absorption of sterolsBody absorbs about 50% of dietary cholesterolDietary fat increases absorptionPlant sterols and dietary fiber decrease absorptionTransportation of Lipids in the BodyLipids packaged into lipoprotein carriers in order to travel in the bloodstreamLipoproteins differ by size, density, and the composition of their lipid coresTransportation of Lipids in the BodyChylomicronsForm in the intestinal tractEnter the lymphatic systemAbout 90 percent fatLiver uses remnants as raw material for very-low-density lipoproteinsTransportation of Lipids in the BodyVery-Low-Density Lipoproteins (VLDLs)Deliver triglycerides to cellsTransportation of Lipids in the BodyIntermediate-Density Lipoproteins (IDLs)Converted to low-density lipoproteinsTransportation of Lipids in the BodyLow-Density Lipoproteins (LDLs)Deliver cholesterol to cellsTransportation of Lipids in the BodyHigh-Density Lipoproteins (HDL)Pick up cholesterol for removal or recyclingRecommendations for Fat IntakeRecommended intakeReduce saturated fat, trans fat, and cholesterolTotal fat: 20–35% of caloriesLess than 10% of calories from saturated fatLess than 300 mg per day of cholesterolRecommendations for Fat IntakeEssential fatty acid requirementsLinoleic acid should provide about 2% of caloriesOmega-6 and omega-3 balanceRatio of 6:1 omega-6 to omega-3 fatty acidsSeafood (fatty fish), canola or soybean oilRecommendations for Fat IntakeCurrent dietary intakesAmericans eat ~33% of total calories from fatAverage calorie intake has increased = Americans consuming more total grams of fatSaturated fat intake ~11%Cheese, pizza, grain-based desserts, chicken, sausage, etc.Recommendations for Fat IntakeRole of fat replacersDifferent types of compositionOlestraSucrose + fatty acidsIndigestible— provides no caloriesReduces absorption of fat-soluble vitaminsLipids and HealthHeart diseaseMajor risk factorsHigh blood cholesterolHigh LDL and low HDL SmokingHigh blood pressureLipids and HealthReducing heart disease riskAHA diet and lifestyle recommendationsConsume an overall healthy dietAim for a healthy body weightAim for a desirable lipid profileAim for normal blood pressureAim for normal blood glucose levelsBe physically activeAvoid use of and exposure to tobacco productsLipids and HealthReducing heart disease riskAHA recommendations Balance calorie intake and physical activity to achieve or maintain a healthy body weightConsume a diet rich in fruits and vegetablesChoose whole-grain, high-fiber foodsConsume fish, especially oily fish, at least twice a weekLimit your intake of saturated and trans fat and cholesterolLipids and HealthReducing heart disease riskAHA recommendations (cont.)Minimize your intake of beverages and foods with added sugarsChoose and prepare foods with little of no saltIf you consume alcohol, do so in moderationFollow the AHA recommendations when eating outside of the homeLipids and HealthObesityHigh-fat diets promote weight gainSignificant within the U.S. population34.9% of American adults17% of American children and adolescentsLipids and HealthMetabolic syndromeAffects ¼ of American adultsCluster of at least three symptomsExcess abdominal fatHigh blood glucoseHigh serum triglyceridesLow HDL cholesterolHigh blood pressureLipids and HealthCancerResults from complex mix of lifestyle, hereditary, and environmental factorsRole of nutrition and diet complexEvidence suggests 30-40% are due to poor food choices and physical inactivitySome dietary factors act as promoters, while others serve a protective roleLipids and HealthCancerDietary and lifestyle factors for reducing cancer riskMaintain a healthful weightAdopt a physically active lifestyleConsume a healthy dietLimit alcohol consumptionLipids and HealthPutting It All TogetherHealthy People 2020 objectives target reducing deaths from heart disease and stroke and reducing the number of adults with high blood cholesterol levels