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1、POLYPHENOLS:Metabolism,Bioavailability&Health BenefitsAt the end of this topic you should be able to:Explain the metabolisms and bioavailability of polyphenols Discuss the health-promoting properties of polyphenolsLearning OutcomesMetabolism of polyphenolsMost flavonoids in our diet are in the form
2、of glycosides.They are deglycosylated by enzymes in the small intestine before absorption.After absorption,they are metabolized by the phase II enzymes to glucuronate and sulfate conjugates.Flavonoids that are not absorbed in the small intestine can be metabolized by colonic microflora aglycones and
3、 phenolic acids Bioavailability studies of polyphenolsNot all polyphenols are absorbed with equal efficacy.Only aglycones and some glucosides can be absorbed in the small intestine,and other polyphenols are not.Bioavailability studies of polyphenolsMax absorption of quercetin-4-glucoside occurs 0.5-
4、0.7 hr,and 6-9 hr for quercetin-3-rutinoside after ingestion of the same quantity.Absorption of quercetin is more rapid and efficient after ingestion of onions than apples.Proanthocyanidins are very poorly absorbed in small intestine.Graefe et al.2001,J Clin Pharmacol.,41:492-499;Hollman et al.1999,
5、Free Radic Res,31:569-573.Hollman et al.1997,FEBS Letter,418:152-156Health-promoting properties of polyphenolsFlavonoids-powerful antioxidant activities in-vitro models,being able to scavenge a wide range of free radicals.Evaluation in-vitro models-using aglycone or glycosides that are present in fo
6、ods.Biological activities of conjugated form(present in plasma or tissues)-Very little is known,due to lack of precision of identification and commercial standard.Cocoa and its polyphenols CVD risk factors Insulin sensitivity Blood pressure Cancer risks Antioxidant defense Inverse correlation betwee
7、n the incidence of coronary heart disease and stroke and the flavonoids quercetin.Women with high consumption of flavonoid-rich foods may prevent CVD.Several other epidemiological studies have confirmed similar associations,although a few are not.Flavonoids vs CHD(Epidemiological studies)Lancet 1993
8、,342:1007-1011J.Nut 2004,134:923-926High dietary intake of flavonols may associated with a reduced risk from CHD mortality in free-living populations (Huxley&Neil,2003,EJCN,57:904-908)Little evidence that flavonoids protect against cancer.(Neuhouser,2004,Nutr.Cancer,50:1-7;Art&Hollman,2005,AJCN,81:3
9、17-325)Several studies reported the protection of flavonoids against neurodegenerative disease,however,it is unclear.A meta-analysis of randomized controlled trials to determine changes in blood pressure due to the intake of cocoa products,indicating that consumption of cocoa-rich foods may reduce b
10、lood pressure(Taubert et al.2007,Arch Intern Med,167:626-634)Polyphenols vs TeaA meta-analysis suggested that tea consumption vs CVD in 2001 found only a small,no significant reduction of myocardial infarction incidence with an increase in tea consumption of 3 cups per day.(Peter et al.2001,Am J Epi
11、demiol,154:495-503)Polyphenols&Women HealthDietary isoflavones have a small protective effect on the risk of breast cancer,but not lignans.(Nutr Res,2006,26:609-619)Isoflavone supplementation may produce a slight to modest reduction the number of daily flushes in menopausal women.(Maturitas,2006,55:203-211)Preventive effects of isoflavones on bone loss and fat accumulation in early postmenopausal women.(Wu et al.,2007;Menopause,14:1-9)Polyphenols-Health benefits Clinical trials“Omic”analysisThank You