Effects of soy protein-isoflavone diet on plasma isoflavone and intestinal microflora in adult mice

Abstract

Effects of supplementing soy protein or casein diet with isoflavones on intestinal microflora and plasma concentrations of lipids and isoflavone metabolites were studied. Male mice were fed a soy protein or casein diet supplemented with isoflavones for four weeks, and feces and plasma samples were collected. Animals were also fed the soy protein or casein diet and feces were collected to investigate the capacity to produce equol from daidzein in vitro. The number of fusiform-shaped bacteria was significantly lower in the soy-isoflavone diet group than in the casein-isoflavone diet group, whereas the number of lactobacilli was significantly higher. No significant difference was observed in the plasma lipid concentration between the soy-isoflavone diet group and casein-isoflavone diet group. Plasma equol concentration was significantly higher in the soy-isoflavone diet group than in the casein-isoflavone diet group. After incubation of daidzein in vitro with the feces from the mice fed the soy protein and casein diets, the production of equol from daidzein was significantly more in the soy protein diet group. The present study indicates that the soy protein diet supplemented with isoflavone has an impact on the composition and metabolism of intestinal microflora and suggests that soy protein plays some roles in the effect of dietary isoflavones on the host through their effects on the intestinal microflora.