Submitted to: Journal of Nutritional Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2006
Publication Date: 1/5/2007
Citation: Heneman, K.M., Chang, H.C., Prior, R.L., Steinberg, F.M. 2007. Soy protein with and without isoflavones fails to substantially increase postprandial antioxidant capacity. Journal of Nutritional Biochemistry. 18(1):46-53.
Interpretive Summary: Tissue damage can be caused by a process known as oxidation. Compounds know as antioxidants are thought to help prevent tissue damage, and thus reduce disease states caused by oxidation. Soy foods have been said to prevent oxidation. This study was conducted to determine if consuming soy protein would increase the antioxidant capacity. The results demonstrated that soy protein consumption does not act as an antioxidant.
Technical 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.