title: Soy protein with and without isoflavones fails to substantially increase postprandial antioxidant capacity.
abstract: Five methods for the assessment of antioxidant capacity [whole plasma conjugated diene formation, low-density lipoprotein oxidation susceptibility, ferric-reducing ability of plasma, oxygen radical absorbance capacity and perchloric-acid-treated oxygen radical absorbance capacity (PCA-ORAC)] were used in a randomized, double blind, crossover study to determine the acute postprandial antioxidant protection imparted by the isoflavone component of soy. On separate days, 16 subjects consumed one of three isocaloric shakes containing 25 g of protein in the form of soy, with 107 mg of total aglycone units of isoflavones, soy with trace isoflavones (<4 mg) or total milk protein. Blood was collected at baseline, 4 h, 6 h and 8 h after consumption. Antioxidant capacity, serum isoflavone levels, fat-soluble antioxidants and plasma vitamin C levels were evaluated. Repeated measures analysis of variance showed no significant differences (P=.05) within treatments over time in four of five antioxidant capacity measurements. Significant differences over time between the soy with trace isoflavones and the total milk protein group were observed using the PCA-ORAC assay. It can be concluded that, on an acute basis, a significant increase in serum antioxidant capacity is not detectable following consumption of soy protein.
authors.affiliation: Department of Nutrition, University of California, Davis, CA 95616-8669, USA.
authors.forename: Karrie M
authors.initials: KM
authors.lastname: Heneman
authors.forename: Hebron C
authors.initials: HC
authors.lastname: Chang
authors.forename: Ronald L
authors.initials: RL
authors.lastname: Prior
authors.forename: Francene M
authors.initials: FM
authors.lastname: Steinberg
mesh_terms: D000975:Antioxidants / Q000032:analysis* / Q000494:pharmacology; D001205:Ascorbic Acid / Q000097:blood; D018592:Cross-Over Studies; D004044:Dietary Proteins / Q000008:administration & dosage*; D004311:Double-Blind Method; D005260:Female; D005290:Ferric Compounds / Q000737:chemistry; D005502:Food; D019833:Genistein / Q000097:blood; D006801:Humans; D007529:Isoflavones / Q000008:administration & dosage* / Q000097:blood; D015227:Lipid Peroxidation; D008077:Lipoproteins, LDL / Q000737:chemistry; D008297:Male; D010084:Oxidation-Reduction; D017382:Reactive Oxygen Species / Q000737:chemistry; D030262:Soybean Proteins / Q000008:administration & dosage*
chemical_list: D000975:Antioxidants; D004044:Dietary Proteins; D005290:Ferric Compounds; D007529:Isoflavones; D008077:Lipoproteins, LDL; D017382:Reactive Oxygen Species; D030262:Soybean Proteins; C004742:daidzein; D019833:Genistein; D001205:Ascorbic Acid