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Lecture 13

NUTR 3210 Lecture 13: micronutrients part 4

7 Pages

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NUTR 3210
David Mutch

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Micronutrients 4 essential trace minerals Iron Ironisfound in a lot of different foodsat lowlevels - Rich in liver,meats,and plant sources(e.g.,leafy greenvegetables,fruits,nuts) Infoods,iron can be found in one of twoforms: 1.heme (within the porphyrin ring of hemoglobinand myoglobin) animals 2.non-heme plants Only twostates of iron are stable in the aqueousenvironment ofthe bodyand infood:Fe (ferric)and 2+- Fe (ferrous) Functions of iron in the body include: 1.oxygen transport (i.e.,important for hemoglobinand myoglobin) 2.redox reactions isan active component oftheelectrontransport chain(ironsulfur centersandcytochrome heme proteins) - Not necessarily not bad,but can promote radicals(contextdependent) 3.iron metalloenzyme (enzymes dont functioniftheydont haveiron) RDA ->8mg/d men,18 mg/d women,27 mg/d pregnancy - Higher for women due tomenses /since womenloseiron - Higher in pregnant women tocover theneedsofthe fetus UL->45mg/d (thisleads to hemosiderosis) Different forms, different absorption Between 10-18%of the iron ingested isabsorbed - How much isabsorbedwilldepend on a personsiron status - /dont want an overloadsoits regulated Non-heme iron - HCl and proteases cleave non-heme ironfrom food componentsin stomach releasing mostly 3+ ferric (Fe ) iron - Stomach acid convertsmost Fe intoferrous iron (Fe ) 3+ - Any remaining Fe isreducedby a reductase in the smallintestine intoFe 2+ - Fe istransported by divalent metal transporter 1 (DMT1) - /allferric ions need tobechanged toferrous ions in order toenter thecell Heme iron - Released from hemoglobin/myoglobin by proteases in the stomach and smallintestine - Heme (porphyrinring) istaken up inthe small intestine by heme carrier protein 1 (HCP1) - Inside smallintestinal cells,the heme porphyrin ring isbrokendown by heme oxygenase into Fe and protoporphyrin 56Factors Influencing Iron Absorption Chelatorsare smallorganic compoundsthatformacomplex withametalion - Thiscan affect iron absorption /can regulateoraffect absorption - If the iron-chelate issoluble,then absorptionisenhanced - If the iron-chelate isinsoluble,then absorptionisinhibited /ifsomeone hashighabsorptionbesttouse insoluble chelator Examplesof enhancers:vit C, and some evidencefor specificsolublefibres(pectin) - Vit C acts asa reducing agent for ferric ion - /favourable state for absorption tochangeFe toFe 2+ Examplesof inhibitors:polyphenols(in tea and coffee),oxalicacid(in spinach),and insolublefibres - Coffee just after a meal reduces iron absorptionby~50% - Oxalic acid bindswith iron (and othermetalstoo),preventingitsabsorption o /insoluble fibres increasetime inthegut and increase competition, Iron distribution and metabolism Iron is transported in the blood in the ferric form bound
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