Antioxidative Functions of Natto, A Kind of Fermented Soybeans: Effect on LDL Oxidation and Lipid Metabolism in Cholesterol-Fed Rats

Natto water-soluble fractions, low-molecular-weight viscous substance, and soybean water extract, which had an inhibitory effect on the oxidation of low-density lipoproteins (LDL) in vitro, were fed to rats for 3 weeks. These fractions had no influence on the growth of rats, which were fed a basal diet containing 1% cholesterol, but lowered plasma triglyceride and total cholesterol. Inhibition of copper-oxidation of plasma and LDL ex vivo, and a reduction in lipid peroxidation in liver and aorta in vivo, were also observed. The antioxidant enzymes were not induced in rats fed natto fraction diets. These results demonstrate that ingestion of the natto fractions led to inhibition of LDL oxidation, and that the fractions perform direct antioxidant action in the body. It is suggested that natto fractions might help to prevent arteriosclerosis, as they appear to reduce lipid peroxidation and improve lipid metabolism. Keywords: Natto (fermented soybeans); antioxidant; LDL; cholesterol; lipid peroxidation; antioxidant enzyme; superoxide dismutase; catalase; glutathione peroxidase; glutathione