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1、1.Abalanceddietisonethatprovidesanadequateintakeofenergyandnutrientsformaintenanceofthebodyandthereforegoodhealth.Adietcaneasilybeadequatefornormalbodilyfunctioning,yetmaynotbeabalanceddiet. Carbohydrates Carbohydratesarearapidsourceofenergy,theyarethebody’sfuel.T
2、hebulkofabalanceddietshouldbemadefromcarbohydrates.Ifeateninanexcessofthedietaryrequirementscarbohydratesareeasilystoredasfatsinthecells,althoughcarbohydrateisthefirstsourceofenergyinthebody. Anaverageadultrequiresabout12,000kJofenergyaday,mostofthisissuppliedbythe
3、respirationofcarbohydratesinthecells. Carbohydratesareusedprincipallyasarespiratorysubstrates,i.e.tobeoxidisedtoreleaseenergyforactivetransport,macromoleculesynthesis,celldivisionandmusclecontraction.Carbohydratesaredigestedintheduodenumandileumandabsorbedasglucose
4、intocells.Sourcesofcarbohydratessuchasstarcharerice,potatoes,wheatandothercereals.Sugarsarealsocarbohydrates,sourcesofsugarsarerefinedsugar-sucrose,whichisafoodsweetenerandpreservativeandfruitsugars-fructose.Ifthedietlackscarbohydratestoresoffataremobilisedandusedas
5、anenergysource. Proteins Proteinisnotadirectsourceofenergyinthebody,itisusedprimarilyforgrowthandrepairofbodytissueswhileremaininganenergysourceasalastresort.Proteinsfulfillawidevarietyofrolesinthebody.Theyarebrokendowninthestomachandintestinestoaminoacidswhichare
6、thenabsorbed.Thebodycanonlyform8aminoacidstobuildproteinsfrom,thedietmustprovideEssentialAminoAcids(EAAs)whicharesynthesisedintoproteinswhichcanbestructural,i.e.collageninbone,keratininhair,myosinandactininmuscle;metabolicenzymes,hemoglobin,protectiveantibodiesandco
7、mmunicativehormones. Sourcesofproteinincludemeat,fish,eggsandpulses.Thedietneedstoprovide8EAAsasthebodyisunabletosynthesisproteinswithoutthesemolecules.2otheraminoacidsaresynthesisedfromEAAssoifthedietlackstheoriginalEAAstheseothertwowillnotbepresenteither.Phenylal
8、anineisconvertedtotyrosineandmethionineisconvertedtocysteine.Cellsdrawuponapoolofaminoacidsforproteinsynthesiswhicheithercomefromdietarypr
