Consumption of soy products increases DNA resistance to oxidative stress in healthy subjects: a pilot study.

Consumption of soy products has been correlated with low incidence of chronic pathologies in which oxidative stress is involved, such as cardiovascular diseases. Isoflavones seem at least in part responsible for the antioxidant effect deriving from soy consumption, but the results of in vivo studies are controversial. In the present study we investigate the effect of a diet including soy products, containing 80 mg isoflavones/day, on antioxidant status in healthy subjects. Eight healthy women followed a dietary intervention of six weeks: control diet (T=21) and soy diet (T=42). At T=21 and T=42 we evaluated in isolated lymphocytes, resistance from oxidative damage to DNA and lipid, by comet assay and malondialdehyde (MDA) production, and glutathione peroxidase (GPX) activity. Lymphocytes -tocopherol, plasma ascorbic acid were also analysed in order to investigate the impact of the dietary intervention on antioxidant status. Finally, plasma concentrations of isoflavones were evaluated to verify the compliance to dietary intervention. Lymphocytes -tocopherol and plasma ascorbic acid did not show significant difference between T=21 and T=42, while daidzein and genistein plasma concentrations significantly increased after soy diet (P< 0.05). Soy diet reduced DNA oxidative damage by about 32% with respect to control diet (P< 0.05), while no significant effect was shown on MDA production and GPX activity. In conclusion, our study suggests that consumption of soy products increase DNA resistance to oxidative stress. This effect should be due to isoflavones because their plasma concentrations were significantly increased after soy diet, while the levels of other antioxidant compounds were unaffected by dietary intervention. However, we can not exclude an influence on DNA resistance against oxidative stress, due to the different nutrient composition between control and soy diets resulting from inclusion of soy products.